What's up with Four (or why aren't you calling the Decorah eaglets "Dx" anymore)?

For the last couple of days, the most commonly asked question on facebook has been something along the lines of "Why are you calling D19 or EWT Four now?" We've also been asked if that means this year's fledglings are going to be referred to as D2, D3, and D4, and what this means for any other birds we've transmitted. I'll start with a recap of our EEE's:

• Four, fka EWT or Eaglet With Transmitter, was first spotted on a road near Decorah roughly a week after fledge began. After a call from police, Bob brought her to his mews for examination and observation and fitted her with a transmitter. She has been rescued twice -- once in a corn field and another time when she was wedged against some woven wire fencing on the ground. She was the one who was relocated to the mulch pile to be with her brother EWOT/Indy. Beak depth and hallux claw measurements taken at the time we fitted the transmitter indicated that she was a female eagle. 
• EWOT, or Eaglet Without Transmitter (aka Indy), has never been picked up and moved elsewhere. It was found at the city mulch piles about 1 mile from the nest. Bob and Brett trapped him on July 4th, attached a transmitter, and renamed him Indy. Sadly, Indy was found electrocuted on July 8th: http://goo.gl/0vjcy0
• SOAR or Mr. SOAR is the eaglet who had surgery at the rehab facility of the same name (Saving Our Avian Raptors). SOAR (the eaglet) is recuperating and we get almost daily updates of his progress. Kay at SOAR and veterinarian Dr. Dirks believe that SOAR is a male eagle based on his size and weight. 

So why the name change? As looks and defining features change, (especially after fledge), Bob preferred to have new nomenclature established since we cannot be 100% sure of IDs. "Four" is the last number of Four's transmitter ID and WOT (Without Transmitter) was an obvious and easily identifying feature (or lack thereof) that could be used to differentiate between the two. After we attached a transmitter to EWOT, Bob and Brett renamed him Indy, short for Independence, because he was captured on the 4th of July. We don't have any plans to change the pre-fledge nomenclature of D + N, so as far as I know we'll start with D21 next year. 

I'm going to close with a quote by William Shakespeare, which seems appropriate both for its subject matter and the Bard's great fondness for falconry metaphors: "What's in a name? That which we call a rose by any other name would smell as sweet." Fly on, fledglings! You are such stuff as dreams are made on!

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Citations

BA1, personal communication and information about Shakespeare's falconry metaphors.
http://www.raptorresource.org/

SE1, personal communication and facebook responses.
https://www.facebook.com/pages/Raptor-Resource-Project/103786266324668?ref_type=bookmark

TW1, personal communication and Ustream responses.
http://www.ustream.tv/decoraheagles

Your Top Thirteen Questions For SOAR and Dr. Dirks

Last week we asked Decorah watchers for their questions about the Decorah fledging that went to SOAR. Thanks to Kay and Dr. Dirks for answering them. Next week we'll ask for questions from Bob and Brett about development and fledge, so stay tuned!

Where will the eaglet be released?
This is a big leap to the end – IF he is able to be released… I think it would be an excellent idea to release him in the NE Iowa area. The exact location will depend a lot on the time of year. We will definitely be too late/too much time will have passed to expect that the Parents would take over any care or guidance. When the time comes we will do some consulting with our eagle experts (Bob and Brett) and find a spot where there is not a current eagle territory – just to avoid any conflicts there – usually the juvies are pretty safe. The big thing will be HABITAT – a good spot for scavenging and fishing. As we know from eagles with transmitters, eagles can travel long distances in short amounts of time. If he is able to be released, he will go wherever he wants to go. 

How do you determine where to release the birds you find, especially if they have been held for a while?
Again – good habitat is what we look for so the birds will not have to work too hard for food. We also look at time of year and weather. Winter is hard for everyone so we hold most birds late November through to early spring for release. Along with the quality appropriate habitat type, we look for travel corridors such as a river. If we release in a resident bird’s territory, which we try very hard not to do, the released bird can easily move to a new spot through the corridor habitat. 

What do you feed your eagles?
We need to mimic the things that they would be eating in the wild the best we can. This helps them to recognize what we are offering as food and is also completely nutritious. We try to give variety. Our eagles really seem to like carp – rough fish that most human anglers do not like to eat – so this helps us with donations of this type of fish. We salvage road killed deer – this meat is rich and dark – lots of vitamins and iron. We have a friend that provides some grown chickens and rabbits.

We start with hand-feeding our extremely ill patients. As they recover, they will eventually take food on their own.

The eaglet looks comfortable with humans. Does it try to bite or how does it react to handling?
A good question. Biting is involved when we need to handle him, so we have big gloves and we handle him carefully yet firmly. Overall comfort is an important part of our care. 
Most of the time our intensive care or ICU patients are in carry crates so we can limit movement. Like humans in ICU units, these birds have severe, often life-threatening injuries or conditions. We provide climate control and make sure that food and water bowls can be seen and are accessible. We also need to be able to easily administer medication and capture our patients to change bandages and perform other necessary tasks.  Of course as they feel better, they want out! When they are ready we have larger flight areas they move into for exercise pre-release. 

This little eaglet would not sit still in a crate. So he is in our small ICU room, which gives him a bit more room to move around. He is quite comfy there right now. 

What is the ICU and what does it look like?
Intensive Care is basically two large rooms and one smaller one that we heat and cool. Check SOAR’s web page for photos of SOAR facilities, including flight areas: www.soarraptors.org

How does the eaglet learn to fly and hunt absent parents?
If they are physically able to fly, they will fly. While skill is learned on the wing, flying and hunting are instinctual. SOAR has a 100 X 20 foot flight area for our eagles. After bone healing is complete, which could take approximately eight weeks or more, our patient will spend time in this large flight area with our other eagles. We have Spirit and Liberty, a bonded pair of non-releaseable education bald eagles that have fostered two different eagle chicks so far in their own large enclosure. He will not need to be fed, but they can model socialization, vocalizations, and eagle behavior. He is well past the age when he would imprint on humans, so we have no worries there. He is not going to like us no matter what!

It's my understanding that bald eagles can present unique challenges in housing and handling. If so, can you elaborate a little?
They are big and powerful. So housing requires large spaces. Handling requires experience and protective gear, including gloves, goggles, and a heavy coat. 

What particular challenges do you anticipate during the Decorah eaglet's rehab, both short term and long term?
We have crossed several hurdles. He survived his initial injuries. His fracture was not compound (bones sticking out of the skin) and was not too severe to surgically stabilize. He went through a successful major surgery. He’ll be on antibiotics to prevent infection and the next step is eating on his own. 

After about three weeks of healing, we will head back to Dr. Dirks for another x-ray to determine the amount of healing and whether or not we can remove the pin. If we can, he’ll have another three to four weeks of limited movement, but no flight attempts yet, since we need to make sure everything is solidly healed. After that, he’ll need physical therapy to get muscles into shape, and of course he’ll need to grow a tail back and we don’t know how long that will take. We will have to see how it goes/grows! 

What percentage of eagles make a full recovery and can be released back into the wild after an injury like this?
We don’t have an answer for that off the top of our heads.  We’ll have a better prognosis at the three week check up.

What is the gender of this eagle?
Judging by size, Dr. Dirks and I both think it is a male. 

Will P's recognize it and care for it or will it just be another eagle to them now?
He is in for a quite long recovery period. He will be with us too long for the parents to be in the mode of caregiving and he will be too old to need them. I don’t know if they will be able to recognize him or not.

How much of the hunting skills are learned vs instinct?
Instinct gets them started hunting and experience hones skill, since there are rewards for doing certain things and disappointment for doing others. 

Do you feel that the break in his/her humerus was due to the owl attack? 
This break is way up in the shoulder area – there is a lot of muscle around the bones there. Owls look big – but they are big puff balls – mostly fluffy feathers. These eaglets out-weigh owls by a lot.  There were no puncture wounds near the break area. I don’t think owls could have done this. Dr. Dirks and I discussed this a bit. This break would take quite a bit of trauma – like being hit by a car. But we just have no way to know for sure what happened. His feathers were grown in well enough to glide/fly from the nest, so it is doubtful leaving the nest would have resulted in this type of break either. [Amy's note: Bob made a similar observation after handling "Four", the fledgling formerly known as EWT. He also confirmed that the eaglets were developed enough to fly].

3rd Decorah Eaglet Found?

We've confirmed a fledgling eagle without a transmitter a little over one mile from the nest. While we can't know for sure, we are quite hopeful that this is our missing eaglet, especially when we compare the data with D14, who was tracked in almost the same location on 6/27/12. We'll be watching to see if the eaglet comes back to N2, appears in N1, or is seen over at the fish hatchery. In the meantime, please stay back and give the eaglet plenty of room if you see it on the ground. Bob reported that the eagle was flying very proficiently this morning.

The NWZ just got a little larger! Thanks to Frank Ermel for the tip and photo. We aren't trying to ID this eaglet at all right now - we've got our hands full just keeping track of everything that's going on. We hope to have an ID post for everyone later today or sometime tomorrow.

A link to D14's late June/early July map for comparison: http://www.raptorresource.org/maps/pdf_maps/761-Map-07-05-12.pdf

Eagle Valley: How did the owl get by Mom and Dad?

We're getting a lot of questions about how the owl could have gotten past Mom and Dad in Eagle Valley. Are Mom and Dad bad parents? Unobservant? Poor protectors? No. However, they are primarily diurnal birds. Although we've seen bald eagles awake and active after dark, they tend to sleep at night: http://www.ustream.tv/recorded/47617300. In contrast, owls are outstanding nocturnal hunters. They fly silently, have very large, tubular eyes with an abundance of light gathering rods, and possess exceptional hearing thanks in part to their facial disks and in part to ear hole placement. The owl could have landed on the nest before either parent was aware of it. When Mom reacted, she may have uncovered her young and unintentionally made them available to the hunting owl.

On February 25, an owl jumped on Mom in Decorah. While she wasn't injured and there were no young in the nest, the video below provides an example of just how silent they can be in flight. Thanks to David Lynch for finding it. If you'd like to read more about owls, click here: http://goo.gl/W0pL0K

We've also been asked why an owl would target an eagle's nest. Owls eat a wide variety of prey and the nest was a potential source of food, adult eagle or not. The eagle nest invaders we've seen include owls, raccoon, red-tailed hawks, squirrels, starlings, sparrows, and mice. Some of them were drawn by eggs and young birds, others wanted nestovers, and one hungry red-tailed hawk attempted to steal prey from Dad in 2011 (clearly visible at 2:15 in the video): http://youtu.be/VbrBUMS_ZPc. Many animals are willing to risk approaching the nest for a meal. Sometimes they are successful and sometimes, like the hawk at Duke Farms last year, they die in the attempt (warning: some readers may find this video disturbing): https://www.youtube.com/watch?v=QqooTTD8sn4

In short, the parents at Eagle Valley are not deficient or lax. I've watched the footage a number of times and I can't hear an owl coming (or see anything). The nest was targeted by a specialist nocturnal hunter who was able to get into the nest before either of the adult eagles were aware of it. We hope the remaining eaglet survives until fledge.

Birds in Flight, or Why Did Dad Fly That Way?

This video shows Dad bringing a freshly killed rabbit to the nest. After pausing in a tree, he circles over a field before landing in the nest with his catch. What is going on? Why did Dad pause in a tree, and why didn’t he fly directly to the nest after taking a break? I’m going to write a little bit about the basics of flight and why Dad might have flown the way he did.

There are four basic forces that govern flight: lift, thrust, weight, and drag.

• Lift pushes birds upwards. Lift is produced primarily by wing curvature, which induces low air pressure on the top of the wing and high air pressure on the bottom. Primary and secondary feathers both help create lift. 
• Thrust propels birds forward. When a bird flaps, its primary feathers twist at an angle relative to the rest of its wing and the bird’s line of flight. This twisting or spinning motion induces low pressure ahead of the bird’s wing and high pressure behind it, aiding forward motion. Depending on the strength of the flap, a bird’s entire outer wing might twist in response. 
• Weight equals mass times the acceleration of gravity, so weight can be defined as the force of gravity on an object. Weight pulls birds down and puts an upper limit on flighted bird size.
• Drag counteracts forward motion. Air passing over the bird’s wing produces friction and creates wingtip vortices that direct the air behind the wing downward, inducing downwash and causing drag. We think birds have a number of ways to counteract drag. Wing slots increase the span factor of bird wings and spread vortices horizontally and vertically, dissipating their kinetic energy and reducing their sucking power. As the bird’s wing is tilted upwards, its angle eventually becomes so steep that air cannot flow smoothly over the surface of the wing and lift decreases. The alula, a small projection on the front wing of birds, can be manipulated to create a temporary slot that allows birds to steeply angle their wings without stalling out. 

Catching prey in flight requires less force, since acceleration, lift, and thrust are already part of the equation. Unfortunately, Dad is on the ground. The rabbit could be adding two or more pounds of weight and has no aerodynamic qualities whatsoever. Dad needs powerful wing flaps and a lot of force to counteract gravity, gain lift, thrust forward, and hoist his rabbit into the air.

Dad takes a breather on a tree limb before bringing his prey to the nest. But if carrying prey is so hard, why doesn’t he fly directly to the nest? Although the angle makes it hard to tell, the tree limb is below the nest and the approach may not have been good. Dad puts gravity to work by dropping from the branch, gaining a little no-cost acceleration. He spreads his wings wide and pitches them slightly back as he launches, catching the air for a little free lift. This reduces the amount of work required to lift and carry prey, since force = mass x acceleration and Dad is using gravity to assist lift - something he can't do from the ground. His spread alula can be seen at 1:11, allowing Dad to steeply angle his wings for a bigger downstroke without loosing his hard earned lift. Note that we don't see the alula in regular flight later in the video.

In short, it’s a lot easier to drop off a high place than fly up from the ground, especially when prey is involved. With a little assist from the tree branch, Dad was able to spiral around at the far end of the field and gain enough lift to drop easily into the nest. Eagles fly so wonderfully that it’s easy to forget how much work and experience goes into it.

Thanks to Rick Black for the video! Check out the Canadian Museum of Nature to see a brief animation of birds in take off, flapping, and gliding flight: http://nature.ca/discover/exb/hwdbrdsfly/index_e.cfm

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Sources

• Gliding birds: Reduction of induced drag by wing tip slots between the primary feathers.
  http://jeb.biologists.org/content/180/1/285
• Alula: http://en.wikipedia.org/wiki/Alula
• Flight and locomotion
  http://www.thewildclassroom.com/biodiversity/birds/aviantopics/avianflightandlocomotion.html
• Forces of Flight: http://howthingsfly.si.edu/forces-flight/four-forces
• Ornithology: Lectures on Flight: http://www.ornithology.com/Lectures/Flight.html
• NASA: Drag due to lift: http://www.grc.nasa.gov/WWW/k-12/airplane/induced.html
• Newtons Laws of Motion:
  http://science.howstuffworks.com/innovation/scientific-experiments/newton-law-of-motion1.htm
  https://howthingsfly.si.edu/flight-dynamics/newton%E2%80%99s-laws-motion

Decorah: Why is Mom Being So Mean to Dad?

We’ve had several questions and comments about Mom’s behavior lately. Why is Mom mad at Dad? Why is Mom so demanding? Why is Mom so mean? While I can find snippets of behavior that would seem loving to human observers – shared incubation duty, mutual nest control, and Dad feeding Mom, to name a few – both adults are going through hormonal changes and their behavior reflects that.

Daylight length, or photoperiod, strongly influences hormone production in birds. In the northern hemisphere, our story begins shortly after the winter solstice in December. As daylight length increases, a cascade of hormones causes birds’ gonads to swell, increasing the production of testosterone in males and progesterone (plus a small amount of testosterone) in females. Testosterone is associated with aggression, territoriality, courtship, nest-building and, in males, testicular development and spermatogenesis, while progesterone, the “pregnancy hormone”, induces egg production in females.

Mom and Dad share incubation duties, so both of them experience another hormonal change once incubation begins. Production of prolactin, a hormone that induces incubation and stimulates brood patch development, rises sharply, while testosterone and progesterone production rapidly decrease. Opioid peptides help stimulate prolactin production, which may be another reason that normally active birds suddenly want to spend the entire day sitting on eggs.

So in the first part of their reproductive cycle, Mom and Dad’s interactions with one another and their young are mediated by hormones that stimulate courtship, mating, territoriality, egg-laying, and lethargy. We humans are moved by their relationship with one another and their tender devotion to their offspring. It’s hard not to see hearts everywhere – I know I did! – as Mom pursues Dad around the nest, Dad brings food gifts to Mom, and both eagles work together to keep their eggs safe from all the extremes Iowa’s winter and early spring can bring.

And then they start shaking the prolactin off.

If the eagles’ earlier behavior added up to love, it’s hard not to see this as its opposite. Mom suddenly seems mean, snappy, or demanding to some watchers. Dad still loves his offspring but seems more distant. In this narrative, our eagle couple is drifting apart – or maybe Mom’s behavior will cause Dad to reject her for a less snappy, more appreciative mate. While compelling to human watchers, this scenario isn’t true.

So what is happening to our eagles? It isn't eagle divorce, but it isn't entirely our imagination, either. As their gonads begin shrinking, they decrease courtship and pair bonding behaviors. As prolactin ebbs, their metabolisms speed up, they become more physically active, their body fat drops slightly, and they probably become hungrier. Mom’s whistling ‘tea-kettle’ makes its first appearance as vocalizations change, although it still stimulates food delivery and/or an appearance by Dad. What we interpret as a falling out is simply a pair of mature, active bald eagles beginning to resume the non-reproductive phase of their lives. To paraphrase Scott Weidensaul, sex hormones pull many strings in a bird’s body. We are seeing that in Decorah right now.

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Things that helped me write this post:

• Bob Anderson, who made me aware of the role hormones play in bird reproduction. He could write a book on the subject.
• Two previous posts: http://goo.gl/xtXUdS and http://goo.gl/OTi6Fb
• Outside My Window (blog): http://goo.gl/Q6S6rq
• Avian Annual Cycles: http://udel.edu/~gshriver/pdf/AnnualCycles.pdf
• Reproductive Physiology Birds of Prey: http://goo.gl/EuPfrq

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Did you know? 

In humans, females are xx (homogametic) and males are xy (heterogametic). But in birds, females are zw (heterogametic) and males are zz (homogametic). Unlike humans, female birds determine the gender of their offspring. http://en.wikipedia.org/wiki/ZW_sex-determination_system

April 22, 2014: Decorah Eaglet Update

April 12, 2014

April 22, 2014

The Decorah eaglets are 20, 19, and 15 days old respectively. What’s happened since April 12?

• Grey, woolly thermal down has almost completely replaced the long white fuzz they hatched with. The last down to be replaced is on the top of their heads. Wigs or mohawks? Either way, we’ll soon see the down replaced there as well.
• They weigh more. Based on Gary Bortolotti’s study Physical Development of Nestling Bald Eagles, D18 should weigh between about 2.5 and 3.3 pounds, D19 should be three to five ounces lighter, and D20 should weigh between about 1.5 and 1.9 pounds. 
• Those crazy clown feet aren’t just our imaginations! The length of their foot pads and mid-toes have nearly doubled since hatch and their tarsi are almost adult thickness, if not length. Their foot pads and mid-toes will reach their maximum sizes when the eaglets are about 40 days of age.
• All three eaglets are thermoregulating, an ability they gained around 15 days of age. Given their rapidly developing feet and new ability to maintain a constant body temperature, we’re seeing much more nest exploration, as first documented on April 17: http://youtu.be/ic_OJr9ioC8. We’re also seeing them spend more time alone.
• They’ve become more coordinated. All three eaglets are becoming more proficient at sitting up, moving around the nest, and pooping without hitting Mom, Dad, or one another. Which doesn’t mean they never hit their parents, as this video of D20 getting Dad shows: http://youtu.be/-Fh_STMNp8w
• Their visual acuity has improved. Our eaglets are watching and focusing on an incoming Mom and Dad, and eagerly reaching out to grasp food instead of waiting for delivery. We’ve talked about the virtuous cycle of feeding, growth, and development. The eaglets’ anticipation of Mom and Dad’s food delivery provides a great example of how feedings help drive development. 
• We have our first 'sun pose':  http://www.ustream.tv/recorded/46510278/highlight/494408
• We won’t see their little earholes for very long, so enjoy them now!

So what do we have to look forward to? We should start to see pinfeathers beginning to show as dark spots on the edges of our eaglets’ wings and tails, which happens at 22 to 28 days of age. Over the next 20 to 25 days, we’ll see a little more development in footpad and middle toe size, and a lot of growth in leg height. Our little eaglets are about to get tall! Stay tuned - we’ve also got a lot of play to look forward to as nest exploration expands and their ferocious growth rate begins to slow around 40 days of age.

[Thanks to Sherri Elliot and David Lynch for help and videos!]

April 12, 2014: Decorah Eaglet Update

Two of our little eaglets are just over one week old! What happened in their first week of life?

• They doubled in size and grew taller. Little peaglets D18 and D19 should weigh about 1 pound now. D20 at 5 days old is about 6-8ozs. Based on what we've been able to find about bald eagle growth, D18 should be about 6+ inches tall, D19 is slightly smaller, and D20 is about 4 inches tall.
• Their eyesight improved. While they can see at hatch, their vision improves in the first seven to ten days. Feeding helps them to develop depth and motion perception, focus their eyes, move them accurately, and use them together as a team.
• Their coordination improved. Our D’s are caught up in a sort of ‘virtuous cycle’ of growth. Eating helps develop visual acuity and strengthens bonds between parents and children. An eaglet’s rich protein diet fuels its incredible growth rate. As eaglets grow and the visual circuits in their brains develop, they see better and become more coordinated. As they become more coordinated, they get even better at eating and exploring, which fuels more growth and exploration.
• They began social interaction. We saw dominance play, “cuddle puddles”, food begging, and adorable bonding between parents and their young.
• They began exploring the world with their beaks. They tasted fish and other food, bonked, bit and nibbled siblings, poked Mom and Dad, and began picking at the nest. As we saw on Friday, they are ready and eager to explore the nest beyond the range of Mom and Dad’s confining feathers.
• Their egg teeth wore away as they ate, nibbled, and explored.

Am I seeing thermal down already? I am! Thicker thermal down will aid eaglet exploration by assisting thermoregulation. Right now, our eaglets can’t thermoregulate properly. They need Mom and Dad to add heat, although they know instinctively how to shed it by panting.

In the week to come, we’ll be looking for more nest exploration, increased sibling interaction, and a change of feathers as thermal down replaces first or birth down. Their little eye masks will begin to fade, and their ear holes (auditory canals) will soon be covered in feathers and out of view.

[thanks to Sherri Elliott for the help!]

Turkey Vulture Mystery!

We have a turkey vulture mystery! As Eaglewhisperer18 recorded yesterday, the turkey vultures returned to their loft in Missouri. TV enthusiasts were thrilled to see them after an unknown turkey vulture destroyed an egg and disrupted nesting last year.

I didn't think we'd see an egg until mid-to-late April, since our TV didn't lay until April 24 last year. I was shocked to learn that at egg had been spotted in the barn today at around 11:45am, and even more surprised to watch the female vulture seemingly pull it out of a corner, absent any laying. The egg was clearly a recently-laid turkey vulture egg, since any eggs laid last year wouldn't have survived a summer in the barn: http://youtu.be/3PV9wg8hrko.

Did our Mom lay this egg? I don't know! She wasn't seen laying it, although the camera wasn't on her the entire time. Complicating matters even further, a video taken yesterday suggests there may have been three turkey vultures in the barn.
http://youtu.be/yul54oscafU

The action goes something like this:

Turkey vulture A flies in in at :02
Turkey vulture B flies in in at :07
A walks back to the nest area at :22.
B walks back to the nest area at :47
B leaves the nest area at :51
An odd flicker or shadow occurs at 1:38. Could this be another TV?
B leaves the barn at 1:42
A (presumably) leaves the nest area at 1:45 and walks to the middle of the barn
Unknown TV M suddenly appears on a bale adjacent to the nesting area at 2:00. It walks toward the door.
A returns to the nest area about 2:20
M follows at 2:47
A TV leaves the nesting area at 3:13 and perches on a haybale
A TV flies out of the nesting area quickly at 3:29, while the TV perches on the bale heads for the door.
The TV by the door wanders back and forth between the barn abd the nesting area until the video ends.

At present time, the female doesn't appear to be incubating the egg and we have no idea who laid it. If you have any suggestions or observations, please let us know in the comments! You can watch live at http://www.ustream.tv/missouriturkeyvultures

Eaglet Questions

Some questions from eagle watchers:

What will happen in the first week?
Like humans and other animals, growing nestlings have developmental milestones. The eaglets spend roughly the first week of their life growing. They aren't able to thermoregulate (control their own temperature) yet, so they will spend a lot of time under Mom and Dad, depending on the weather and temperature. We'll see them eat, sleep, scuffle, and grow stronger as they interact with one another. They will probably lose their egg tooth in the first week, but they will not change color until they are a little older.

Here is a slideshow from the first week in 2011. The eaglets are noticeably larger and stronger by the end of the week, although they aren't exploring much yet.


How big were the babies when they hatched?
The quick answer: not very big! Unlike poultry, waterfowl, and even some commonly used falconry birds, it isn't easy to find data on bald eagle hatchling weight. According to the paper 'Physical Development of Nestling Bald Eagle Growth with Special Emphasis on the Timing of Growth Events', written by Gary Bortolotti, the average hatch day weight of bald eagle hatchlings at Besnard Lake in Canada measured 91.5 grams, or 3.2 ounces - roughly the same weight as 18 nickels. I suspect that our little "Ds" would weigh roughly the same amount, although Bald eagles get bigger the farther north one travels: a phenomena known as Bergmann's Rule.

I collected 18 nickels and held them in my hand. It isn't much.

How fast do the eaglets grow?
The quick answer: fast! The maximum nestling weight gain for Bald eagles appears to be the greatest in North America. From the same paper by Mr. Bortolotti: Male hatchlings had an average growth rate of 102 grams (roughly 3.5 ounces) per day, while females averaged 130 grams (roughly 4 ounces). However, their growth occurs along a curve, not a straight line, with the highest percentage of weight gain per day occurring in the first 30 days.

Math Warning! Regular readers might recall that I used the fibonacci ratio of 61.8% to try to determine nest weight. This is a number that turns up all the time in nature, especially in spiral shapes. Those of you that really love math will be pleased to hear about the Gompertz function: a model that describes a time series where growth is slowest at the beginning and end of the series. Like the fibonacci ratio, this turns up all over the place: eaglets, tumors, population curves, and market saturation can all be modeled with the Gompertz function. This chart shows the pattern of the eaglets' growth as a curve from somewhat line-like through very curve-like to almost line-like again. This special kind of curve is called an asymptote: a kind of curve who's curvature approaches zero as it tends towards infinity. Put simply, it becomes more line-like and less curve-like the longer it goes. Note how steep the curve is between 0 and 1 when considered as a percentage of the asymptote. That's a fast-growing animal, and most of its weight gain, relative to its overall body weight, occurs early on.

This chart was reprinted from The Wilson Bulletin 96: 527 from an article published by G. R. Bartolotti (1984) with the written permission of the Wilson Ornithological Society.

Of course, not all body parts follow a nice neat curve. Again, back to Bortolotti's paper: the legs of the nestlings he studied appear to have reached full size about halfway through the nesting period, but the flight feathers and bill didn't attain mature size (or, in the case of the feathers, mature juvenile size) until after the eaglets left the nest. Similarly, their flight muscles don't fully develop until after they've started flying. Like so much else in nature, what looks like a simple question turns out to be surprisingly complicated. In general though, fast works well to describe eaglet growth.

What about Cain and Abel Syndrome?
A lot of people are worried about Cain and Abel Syndrome - the harassing or killing of a smaller, weaker sibling by a bigger, stronger sibling. In the case of the eagle nest, the first born eagle is most likely the largest and strongest. As those crazy growth curves make clear, it might have a substantial advantage in size and weight over its siblings.

Having said that, this nest has a very good history of producing young. While the siblings still harass one another, the area's abundant food supply helps mitigate the affect of Cain and Abel Syndrome. I don't like to make predictions about wildlife, but we haven't seen one die as the result of Cain and Abel Syndrome yet. The harassment will slow as sibling growth achieves parity: not unlike some human families I can think of!

This razzle video from 2012 shows sibling competition.


What is a Crop?
The crop is muscular pouch in the esophagus that stores food and regulates its flow through the digestive system. A distended crop can look quite alarming, but it just means the babies are digesting a recent meal. When our moderators talk about crops, they are usually pointing out that the babies are full or answering a worried question ("What is that?!"). That bulgy-looking thing at the top of the babies' chests? That's a full crop.

This raptorfan video from 2012 shows a feeding:


Where does the word pip come from?
This is one of the things I like about our watchers - they always come up with new questions that I would never have thought of asking. Pip has a number of meanings, but it appears that this useage might come from 'pip' in the sense of 'spots found on dice or playing cards' and is derived from the old English word peep. I recommend googling this one - it's a fun word to explore.

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Things that helped me learn and write about this subject:

• The Wilson Ornithological Society - thank you for your permission.
• Journal of Wildlife. Management 57(1):10-19. Bortolotti, G.R. 1984. Physical development of nestling bald eagles with emphasis on the timing of growth events.
• Asymptote: http://en.wikipedia.org/wiki/Asymptote
• Gompertz Function: http://en.wikipedia.org/wiki/Gompertz_function
• Bob Anderson
• The Word Detective: http://www.word-detective.com/2008/03/24/pip-the/

Big Jump at Eaglecrest

The Big Jump happened at Eaglecrest on April 1 at 4:42PM PDT, although it didn't go quite as expected. We believe that Wilma laid seven eggs of her own and incubated four additional eggs laid by Trudy, the intruder goose. Six goslings hatched. Of those six, four jumped at roughly 24 hours and two were unable to rise to their feet. All four that jumped made it safely to the pond.

Canada goslings are precoccial birds. They require very little direct parental care or feeding following hatch. Their parents will protect them from predators and other geese and help them find food, but they don't incubate the young after hatch or bring food to them in the nest. Canada goslings need to be able to get on their feet quickly, since the entire family leaves the nest roughly 24 hours after hatch starts.

The goslings that didn't jump were never able to get to their feet or move significantly from one place, which indicates they experienced some kind of damage during development in the egg. One of the goslings had already completely dried off, indicating hatching had happened some time ago. The other, while still wet, was unable to get up or propel itself at all. Canada goose hatchlings should be able to come to their feet very quickly once hatched. That those two didn't indicated something was wrong.

So why did two of the embryos fail to develop properly? We don’t know for sure. The eggs could have been injured in the struggles between Wilma and Trudy or damaged because Wilma couldn’t incubate, turn, or aerate all eleven eggs properly. From our point of view, two goslings died without reaching their feet and one egg failed to hatch. But from the goosey point of view, four goslings survived to fledge. Would waiting another twelve to twenty hours have saved the two goslings that failed to rise? No, but it might have harmed the successful hatchlings, who needed nourishment they couldn't get in the nest. Fred and Wilma gave their healthy, living offspring an excellent chance at survival by jumping when they did.

Some video of the goslings from Eaglecrest:

New goslings – MsDebbiB: http://youtu.be/DAp15Xu_rm8
Gosling leg stretch – Eaglewhisperer18: http://youtu.be/QsOIW3VKG2g
Wilma’s little goslings – Mocha Mama: http://youtu.be/uxnIZVrAzGU
The Jump! – Mocha Mama: http://youtu.be/sUHSmVge3-0
Waddle to the pond – Mocha Mama: http://youtu.be/C91I5Pl_pqA
Goslings swim - MsDebbiB: http://youtu.be/LijKt2jfczc

To learn more about incubation and heat/cold damage, follow this link:
http://www.brinsea.com/customerservice/poweroff.html

To learn more about the differences between altricial and precoccial birds, click here:
http://goo.gl/qC70ut

Houston, We Have An Eagle!

Presenting D18! The first bald eagle egg in Decorah hatched today at 9:22AM CDT, bringing the total number of young produced on this territory to 18 so far. The eagles laid egg #1 on February 23rd, at 4:55pm, egg #2 on February 26, at 5:33pm, and egg #3 on March 2, at 6:43pm. Given the extreme cold and heavy snow, we weren’t sure any of the eggs would hatch. However, the eagles persevered through -40F windchills, direct temperatures of -20F, multiple snowfalls, one of which covered the nest with over ten inches of snow, and drenching rain. They diligently cared for their eggs, taking brief breaks from incubation only when the weather allowed and working almost continuously to bring fresh material in for the nest cup. We are thrilled that their skill and perseverance paid off! We’ll be watching to see if and when the other two eggs hatch. We invite you to watch with us live at http://www.ustream.tv/decoraheagles

Congratulations, Mom and Dad Decorah! We'll be posting video as it comes in, but here are a few to get everyone started:

• Welcome, D18! http://youtu.be/c2WqbBNhquk
• Happy Birthday D18! http://youtu.be/KETKIDkIs04
• First Hatchling: http://youtu.be/3INl0XaWark
• Little Wing Pops Out: http://youtu.be/zBeF4mVjP0U

#DecorahEagles #RaptorResource

First Hatch at Fort St. Vrain!

The first bald eagle egg hatched at Fort St. Vrain on Tuesday, April 1. Watcher Eaglewhisperer18 caught pip at at 11:50PM CT on March 31, and a eaglet was confirmed on camera at 8:42AM CT.

The eagles have nested here since before 2003 and have produced 15 young to date. Spring weather can be very rough here. The nest failed in 2009 and 2011, when sudden spring snowstorms covered the nest, causing the eaglets to freeze to death. Just one eaglet, nicknamed 'Survivor' by fans, lived through a snowstorm last year.

The nest can be watched at http://www.farmyou.com/falcon_cams/index.html. Click the 'Fort St. Vrain Eagles' link to view.

Three Bald Eagle Eggs at Fort St. Vrain!

We have three bald eagle eggs at Fort St. Vrain, and the camera is back! The eggs were laid as follows:

• Egg #1: February 21
• Egg #2: February 24
• Egg #3: February 28

The eagles have tended to be closer to 39 days here, so the eggs should start hatching on roughly April 1st. April 1st might be a very busy day for us, since it's also the first possible hatch day in Decorah and the projected 'jump' day for Canada geese Fred and Wilma's brood at Eaglecrest, assuming hatch happens there on March 31st. 

To watch Fort St. Vrain online, visit one of the links below: 

• http://birdcam.xcelenergy.com/eagle.html
• http://www.farmyou.com/falcon_cams/

When will the eggs hatch in Decorah?

We've had a lot of people ask when the eggs will start hatching in Decorah. Mom laid the eggs as follows:

• Egg #1:02/23/2014 @ 4:55pm
• Egg #2:02/26/2014 @ 5:33 pm
• Egg #3:03/02/2014 @ 6:43pm

As several of our mods have pointed out, this almost exactly mirrors 2011. So if the hatch occurs as it did then, we should see hatch #1 on April 1, hatch #2 on April 3, and hatch #3 on April 6. However, eagle eggs can take from 35 to 39 days to hatch, and the spring of 2011 was unusually warm and dry. If we go with the 39 day figure given this year's extreme cold, hatch #1 should start on April 3, hatch #2 on April 6, and hatch #3 on April 10.

In short, we're predicting that the hatch could start any time between April 1st and April 5 based on what we know about the eggs, the eagles, and the weather. We'll be watching Mom & Dad as they roll the eggs to see if they just roll them, or if they stop and stare, looking for a pip hole or listening for a chirp from inside the shell, and offering chirps back as encouragement for the chick to chink away at the egg.   The pipping process can take from 12-24 hours before the hatchling emerges. Stay tuned!

Canada Goose Update

The goose and the hawk. Hawks drive the
intruder from their nest.

In the last blog, I speculated that Wilma's nest intruder could have been dumping eggs. It looks like she dumped not one, but two! From Eaglecrest:

Canada goose Mom Wilma is incubating NINE EGGS...seven of her own and two laid right in her nest by a female intruder. The two "foreign" eggs were laid on 3-15 and 3-22. In both cases, Wilma relentlessly attacked the intruding goose until she left. We may not have seen the last of her. The two intruder eggs will not hatch with Wilma's...they are eleven days or more behind schedule. Wilma began full time incubation of her SEVEN eggs on Tuesday, March 4th. We will expect the little goslings to hatch around March 31st...with the "big jump" about April 1st. Mate Fred is in constant protection mode, as usual.

We've been asked why this goose is behaving so strangely. Why is she dumping eggs? Why is she trying to sit in a hawk nest? I'm speculating that our invader is responding to the recent death of her mate. I haven't seen her accompanied by a male, which is extremely uncommon. Mated male geese are almost always hovering around their nesting mates, protecting them from predators and other geese. A study done at Horicon March in 1959 indicated that reduced breeding productivity was almost entirely connected with goosey social behavior. The authors of the paper wrote: 

"Over half the birds assumed to be capable of breeding failed to make nests in which they laid and incubated eggs; one-fifth of the birds failed even to pair up effectively. The nine pairs that failed to lay eggs in nests were involved in unusually frequent territorial clashes, and most of them were unable to maintain stable territories for any length of time. Four of the 5 pairs (and perhaps all 5) that lost their clutches did so because of disturbance to the female from other geese, related to a lack of effective male defense."

So our unknown intruder doesn't have a male to help safeguard her nest from other geese, who can be very disruptive to laying and sitting. What seems like erratic behavior is really an attempt to produce young under extremely difficult circumstances. While the intruder's eggs won't survive this spring, she'll most likely pair up with a new male goose to try again in 2015. There is no shortage of geese at Eaglecrest!

Geese have an elaborate, shifting hierarchy ruled by ganders with large families. I'll write a little more about the importance of family once the eggs start hatching. To watch Eaglecrest live, go to http://www.ustream.tv/eaglecresthawks. We anticipate hatch in Wilma's nest at the end of March or very early in April. 

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Resources

Social Behavior and Breeding Success in Canada Geese (Branta canadensis) Confined under Semi-Natural Conditions
Nicholas E. Collias and Laurence R. Jahn
The Auk
Vol. 76, No. 4 (Oct., 1959), pp. 478-509
Published by: University of California Press
Article Stable URL: http://www.jstor.org/stable/4082315

Some of what we're seeing could also be a response to crowding, which impacts reproductive and social behavior. As California's drought reduces water resources, birds and other animals crowd more densely around those that remain. We'll explore the impact of crowding in a future blog.

What happened at Eaglecrest on Saturday?

Why did another Canada goose sit on Wilma’s eggs for 27 minutes? Why didn’t Wilma’s mate Fred help remove the invading goose? We’re getting a lot of questions about what happened at Eaglecrest on Saturday, March 15.

First, a recap: At 6:49PM PST, an unknown goose settled on Wilma’s eggs. Wilma spent the next 27 minutes trying to evict the invader by nibbling and chewing on her side, wings, and neck. The intruder eventually left without responding to Wilma’s defense. Wilma immediately settled back down over her eggs, incorporating the down she’d plucked from the invader into her nest. Fred didn’t attempt to drive the invader or Wilma from his nest, and there was no interaction with or harassment from other geese. So what was going on? And why didn’t Fred help?

Canada Geese and Reproduction
At one point, it was thought that Canada geese were strictly monogamous. Close observation has yielded a more nuanced picture. Most Canada geese do not breed until their fourth year, but younger geese may form unstable pair bonds and simulate or engage in breeding behaviors, including copulation. Although sexually mature Canada geese tend toward monogamy, extra-pair copulation and intra-specific brood parasitism (egg dumping) occur at higher rates than once thought. A study of 253 free-living Canada geese in 42 clutches over 3 breeding seasons found that:

• About 60% of clutches were free of parasitism or extra-pair fertilization
• About 14% of clutches included eggs that were unrelated to the host male, which indicates extra-pair fertilization on the female's part
• About 26% of clutches included eggs that were unrelated or semi-related to the host female, which indicates parasitism or egg-dumping on the part of another female

Sheer speculation #1: The invader attempted to dump an egg in Wilma’s nest
The same study revealed that egg dumpers tended to be closely related to egg dumpees. Is this a deliberate collaboration between mothers, sisters, and other closely related females, or simply a consequence of families living closely together? It’s an intriguing question and one that deserves more study, especially since family size, aggression, and social dominance all impact nest success and survivability of young. Eaglecrest’s facilitators told me that they believed the invader was a related bird – possibly a daughter – and similar behavior was observed last year as well. So was this a related adult goose looking to dump an egg in Wilma’s nest? If so, she failed. Seven eggs were counted in the nest prior to and immediately after the intrusion.

Could the invader have been an immature goose? Younger geese have been witnessed engaging in adult behaviors, including copulation and pair-bonding. Bonded youngsters have been observed maintaining territory and building nests, although they don’t lay eggs. At least one observer believed this was an immature bird. If she was, it might explain why she attempted (but failed) to drop an egg. Perhaps hormonal activity (and maybe immature pair-bonding?) compelled her to try to lay or incubate eggs she didn’t have.

Sheer Speculation #2: The invader was attempting to take over the nest site and pair with Fred
While Canada geese aren’t as monogamous as we once thought, pair-bonding and family are extremely important in their lives. According to one study, single immature Canada geese were 1.44 times more likely to die or disappear than immature Canada geese that belonged to a family. Social status is tied to family, and family is a matter of life and death. Perhaps our invader didn't have a family or had recently lost a mate. She may have been trying to pair with Fred. Alternatively, she could have been under a compulsion.  If her previous mate and nest had been largely destroyed shortly after the onset of incubation, she might have been hormonally compelled to incubate eggs, which would explain her persistence.  Even more strangely, she might have fixated on Fred or the nest itself. Collias and Jahn wrote that “Subordination to dominating geese, inability to establish a foothold against the resistance of territorial incumbents, and unsuccessful fixations on certain nest sites or on certain individuals as potential mates, all serve to delay…effective breeding by many individuals.” This seems like the less likely scenario, since unpaired geese don’t usually disturb nesting pairs. But I can't rule it out, either. Maybe this kind of behavior is more common than was once believed, or has become more common as populations have expanded and increased in density. Only the geese know for sure.

So why didn't Fred help Wilma? And why didn't the invading female respond to Wilma?
Male geese protect their mates from a variety of things, including other male geese. Male geese have been known to kill one another over mates, harass and disrupt nesting, and engage in extra-pair fertilizations. By defending his mate from other males, Fred assures that the goslings hatch successfully and are all his. A non-aggressive, presumably unmated female was no threat to Fred's paternity or eggs. However, she was clearly a threat to Wilma, who responded accordingly. We've also been asked why the invading female didn't respond to Wilma's pecking and down pulling with hissing, flapping, or honking. Perhaps she was trying to prevent triggering an aggressive response from the larger and more powerful Fred. Similar 'quiet' strategies have been noted in Canada geese who are accompanying newly hatched goslings on their first trip from the nest. By remaining quiet, parents avoid triggering an aggressive response from other nesting geese that could damage or kill their young.

It can be disappointing to find out that birds don’t necessarily model human ideals of fidelity or cooperation, especially when the birds in question have a reputation for monogamous behavior. I think professor and ornithologist Bridget Stutchbury put it very well when she wrote “There are many similarities in how competition and conflict have shaped the evolution of behavior among animals, but we must not forget that birds do not have the same feelings, thoughts, or decision-making processes as humans.” I look forward to seeing what happens once the nests start hatching. 

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Resources

Social Behavior and Breeding Success in Canada Geese (Branta canadensis) Confined under Semi-Natural Conditions
Nicholas E. Collias and Laurence R. Jahn
The Auk
Vol. 76, No. 4 (Oct., 1959), pp. 478-509
Published by: University of California Press
Article Stable URL: http://www.jstor.org/stable/4082315

Reproductive Success and Survival in Relation to Experience during the First Two Years in Canada Geese
Dennis G. Raveling, James S. Sedinger and Devin S. Johnson
The Condor , Vol. 102, No. 4 (Nov., 2000) , pp. 941-945
Published by: University of California Press on behalf of the Cooper Ornithological Society
Article DOI: 10.2307/1370326
Article Stable URL: http://www.jstor.org/stable/1370326

Some Associations of Behavior to Reproductive Development in Canada Geese
Jack S. Wood
The Journal of Wildlife Management , Vol. 29, No. 2 (Apr., 1965) , pp. 237-244
Published by: Wiley on behalf of the Wildlife Society
Article DOI: 10.2307/3798427
Article Stable URL: http://www.jstor.org/stable/3798427

The History and Breeding Biology of the Canada Geese of Marshy Point, Manitoba
James A. Cooper
Wildlife Monographs , No. 61, The History and Breeding Biology of the Canada Geese of Marshy Point, Manitoba (Jul., 1978) , pp. 3-87
Published by: Wiley on behalf of the Wildlife Society
Article Stable URL: http://www.jstor.org/stable/3830608

http://www.science20.com/anthrophysis/urban_goose_reproductive_decisions_are_not_impacted_their_population_densities-86374

Canada Geese: Precocial versus Altricial

Three Canada geese at Eaglecrest are currently sitting on eggs. "Wilma", in the home tree, has laid seven eggs to date. She started full incubation on March 4th, which puts her hatch between March 27 and March 31. Betty has three or more eggs in the east pond nest, and Lucy has two or more eggs in the elevated pond nest.

The most common question about Eaglecrest's Canada geese is probably "How will the parents feed so many young?". While large broods are fairly common in many kinds of birds, Canada geese don't have to feed their young. Read on to learn more!

Precocial versus Altricial
From Stanford University:  A precocial bird is "capable of moving around on its own soon after hatching." The word comes from the same Latin root as "precocious." Altricial means "incapable of moving around on its own soon after hatchling." It comes from a Latin root meaning "to nourish" a reference to the need for extensive parental care required before fledging in altricial species. 

So what's the big difference? Precocial birds like Canada geese lay energy-rich eggs to support the greater in-egg development of their young, who hatch ready to go. Their large, energy-rich eggs may contain almost twice the calories per unit weight than the eggs of altricial birds, which means that precocial females must obtain abundant food resources before laying eggs. Altricial birds like bald eagles, barn owls, and peregrine falcons do not have such large nutritional demands before egg-laying, but they have to find sufficient food once their helpless young hatch. While individual precocial birds are vulnerable to predation, it is much less likely that an entire brood will be eaten or destroyed. Altricial young cannot leave the nest prior to fledging, while precoccial young leave the nest quickly and have some ability, even when very young, to avoid predation.

Stanford University also tells us that there seems to be a trade-off in bird brain sizes related to the the degree of precocity. Precocial species have relatively large brains at hatching, but their adult brains are smaller relative to body size (the brain/body-mass index) than those of altricial birds. While altricial young hatch with smaller brains, they have highly efficient digestive tracts and a rich, parent-provided diet. Post-natal brain development is great and adults have proportionally larger brains than precocial species. Is this because they have more energy available to grow larger brains, or is something else going on? We're still trying to figure it out. This abstract hypothesizes that delaying brain development (by lengthening childhood) gives brains a longer period of time to grow and become more complex: http://goo.gl/sNw3xe.

At any rate, our hatchlings face very different challenges. Precocial Canada geese are relatively mature and mobile from the moment of birth, unlike altricial Bald eagles, Barn owls, and Peregrine falcons. Eagle, owl, and peregrine parents bring food into the nest for their young, often caching or storing prey for later consumption. Their young don't need to leave the nest or procure food until they fledge. The young goslings leave the nest within 24 hours of hatching and do not return to it. While their parents continue to provide protection and care, the goslings feed themselves.

The precocial goslings are also able to thermoregulate right away, unlike the eaglets and owlets. Altricial birds require their parents (or a parent) to apply warmth until their down feathers are developed enough to insulate them. The eagle parents and mother owl will spend a great deal of time huddling over their young after they have hatched, but the Eaglecrest geese will take to the water quite quickly, with no huddling required.

Eaglecrest offers a plethora of wildlife, including Canada geese, for watching. Visit http://www.ustream.tv/eaglecresthawks to see them! Again, we are anticipating goose hatch some time between March 27 and March 31.

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Resources

Stanford University, Altricial and Precocial: http://www.stanford.edu/group/stanfordbirds/text/essays/Precocial_and_Altricial.html

Patterns of Metabolism and Growth in Avian Embryos

Carol Masters Vleck, David Vleck and Donald F. Hoyt

American Zoologist , Vol. 20, No. 2 (1980) , pp. 405-416

Published by: Oxford University Press

Article Stable URL: http://www.jstor.org/stable/3882403

The Evolution of Parental Care in Birds

A. Ar and Y. Yom-Tov

Evolution , Vol. 32, No. 3 (Sep., 1978) , pp. 655-669

Published by: Society for the Study of Evolution

Article DOI: 10.2307/2407731

Article Stable URL: http://www.jstor.org/stable/2407731

Developmental Modes and Developmental Mechanisms can Channel Brain Evolution
http://openi.nlm.nih.gov/detailedresult.php?img=3037498_fnana-05-00004-g003&req=4

Eggs and Incubation

Why are the eagles off their eggs? Will the eggs survive? What happens during incubation? These are just a few of the questions we get about incubation. I'll see if I can answer some of them here.

An infertile chicken egg. See the blastodisc?

Unlike most birds, chickens will lay eggs even when a male isn't present. We'll start with a quick look at an unfertilized egg, pictured at right. From the Chicken Chick: An infertile egg contains only the hen's genetic material, which means a chick can never hatch from that egg. The hen's genetic material, termed the blastodisc, can be identified on infertile eggs as a light-colored dot with irregular borders. Every egg contains a blastodisc. My breakfast, at right, is an infertile, organic, cage-free 'Egg-Land' chicken egg. The blastodisc can be seen in the center of the egg. If the egg is fertilized, the blastodisc turns into a blastoderm - the first stage of embryonic development. End stage? Hatchling bird!

Let's assume we have a fertilized egg, discussed here. As the embryo develops, it will consume both the fatty egg yolk and high-protein egg white. By the end of day two, our little chicken will have a heartbeat. Its beak and egg tooth will begin to form on day six, and its feathers on day eight. By day nine, it will begin to look somewhat like a bird, and its mouth opening will form. On day thirteen - well, just go look at this blog for the rest.

So what does the developing embryo need to survive? We discussed the importance of temperature here, but incubating birds (or incubationist humans) also need to control humidity, move or turn the eggs, and make sure the eggs are well-ventilated.

Keeping Eggs Alive
Why were the eagles off the eggs so long on March 7th? We were asked this question on facebook, ustream, and via email. I think the eagles may have been giving the eggs a chance to dry out and breathe.

A bird's eggshell has thousands of tiny pores, which allow water and gas to pass through. Mammals like us get oxygen through an umbilicus, but developing birds receive oxygen and remove carbon dioxide through the egg shell. Gases, including oxygen, enter and leave the egg by diffusing through the pores in its shell, across the outer and inner shell membranes, and into the blood in the capillaries of a special tissue called the CAM, or chorioallantoic membrane. As the weather warmed in Decorah, the snow began to melt and the humidity soared. Condensation can form on eggshells exposed to excessive humidity, which clogs shell pores and provides a vehicle for bacteria. The result? Fatal suffocation and/or contamination. Only the eagles know for sure, but I think they may have responded to the threat of rising humidity levels by leaving their eggs uncovered. Standing or leaving entirely allows fresh air to circulate over the eggs, dropping the humidity level and giving the developing embryos fresh air. Turning or rolling assists air exchange, helps maintain an even egg temperature (especially in big egg piles, where outer eggs may be cooler than inner ones), and keeps the developing embryo from sticking to the eggshell.

In short, most bird eggs require specific temperatures, proper humidity, regular movement, and air exchange. Birds provide these by applying body heat, standing and/or leaving for periods of time, and rolling or turning their eggs. In birds, incubation is both an instinctive and learned behavior  - while birds will automatically incubate eggs or egg-shaped things, they get better at incubation with experience. There are no guarantees,  but Mom and Dad are skilled incubators with a long history of brooding together. Watching them meet the challenges of their environment gives me hope for their eggs. Go eagles!

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Resources

Bob Anderson, personal communication.

The Chicken Chick. This is a really neat site for those of us who love chickens!

• Facts and Myths About Fertile Eggs
• Chicken Embryo Development

Brinsea. For all your incubation needs.

• Humidity in incubation

Texas A&M.

• Incubating and Hatching Eggs

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Did you know?

We usually talk about birds, but people also incubate snake eggs! This video from Snake Bytes discusses the ins and outs of snake incubation: http://youtu.be/JlSS5wap-Zc

Eggs and Cold Weather

Mom with eggs on February 26, 2014

Everyone is worried about the eggs in Decorah. Iowa is facing extremely cold temperatures in the weeks to come. While there have been other cold years – 2008, for example, had sub-zero temperatures into early March – this looks like one for the record books. We can’t guarantee that the eggs won’t freeze, but I thought I’d talk a little bit about eggs and cold damage.

Much of what we know about eggs and temperature comes from incubationists, or people who incubate eggs. Temperature, humidity, and regular turning are all important to insuring an embryo’s survival and eventual hatch. In 1969, H. Lundy identified five temperature zones characterized by their effect on the developing embryo. These studies were carried out on chicken eggs in an artificially controlled environment, but we can look to them for some idea of how the eggs in Decorah and elsewhere might respond to ambient temperature.  The five zones are:

• The zone of heat injury or death:  Above 104.9°F or 40.5°C.
• Optimal temperature, aka the zone of hatching potential: 84.5° to 104.9°F or 35 to 40.5°C. The American Eagle Foundation lists this temperature as 99° for bald eagle eggs incubated in an artificially controlled environment.
• The zone of disproportionate development: 80.6 to 95°F or 27 to 35°C. Embryos in eggs that spend too much time in this zone can develop unevenly, leading to crippling injuries or death. Successful hatching is greatly reduced.
• The zone of suspended development: 28.4 to 80.6°F or -2°C to 27°C. Eggs at this temperature don't develop at all. Freshly laid eggs can spend a lot of time at this temperature with no harm to the egg or embryo. 
• The zone of cold injury or death:  Below 29°F or -2°C. Although eggs contain a great deal of water, they can get colder than 32°F/0°C without freezing. However, eggs that reach 29°F will freeze, which usually causes death. Some exceptions to this rule have been recorded in Mallard ducks.

So what does it all mean? 
In the last couple of days before egg-laying, we watched Mom and Dad build a wonderful nest bowl or cup of soft dry grass and shredded cornstalks. The grass conforms to the eggs, wrapping around to provide warm, dry insulation below and around them. Mom and Dad transfer heat from their bodies and regulate temperature by alternately sitting on or standing away from the eggs. Of course, this year has been cold enough that they’ve spent very little time standing. Sitting low in the nest helps keep the eggs and incubating parent warm. One of our facebook fans compared it to Tupperware – a great analogy, since the eggs are cupped below and sealed above. We've also watched the eagles bring in extra cornhusky insulation this year, building their pile as the cold deepens. The eagles may be on to something, since in 2009 the US Department of Energy awarded $200,000 to Husk Insulation, a company that makes insulation from cornhusks. The  company's panels are 10 times more effective than conventional insulators like foam.

So how warm are Mom and Dad? In a study of overwintering bald eagles, Mark Stahlmaster found that adult bald eagle average body temperatures ranged from 102.2°F, or 38.9°C, to 106.1°F or 41.2°C. Ambient temperature, wind, precipitation (snow can be insulative, but rain is not), shelter, and time of day all had an impact on body temperature. Since the zone of heat injury can be lower than the body temperature of an incubating adult, it’s easy to see why Mom and Dad might (in warmer weather) spend time away from their eggs. Although Dad has taken his share of egg duty this year, I wonder if larger Mom might spend more time incubating in extremely cold weather or at night, when eagles can drop their body temperature to reduce energy loss. Larger animals have an easier time conserving heat, since they have lower area-to volume ratios. While Mom isn’t that much larger than Dad, it might make all the difference in a cold weather event.

Lundy’s work was based on artificial incubators, where temperature and humidity can be tightly controlled. Mom and Dad live in the real world, subject to real weather events. Yet they have an excellent record of hatching eggs. Can we guarantee that the eggs won’t freeze or suffer cold damage? As much as we’d like to, we can’t. But Mom and Dad are diligent, experienced parents with a well-built nest cup, a long-term territory, and a good food supply. They are spending a lot of time clamped down on their eggs, applying heat from their very warm bodies directly to the eggs. Unlike us, they don’t need an instruction manual to provide information about temperature regulation, egg-turning, or care. We are watching and hoping for the very best. Go Decorah Mom and Dad!

PS: Sherri Elliott has mentioned the difference in the egg ‘line-ups’  - Mom incubates the eggs in a triangular pattern, while Dad incubates them in a straight line. This almost certainly has to do with the size difference between the two (and the overall area of their brood patches), although ‘shapes’ are not uncommon. Like sitting and standing, shapes and positioning can help regulate temperature and keep eggs alive.

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Resources

Stalmaster, Mark V., and James A. Gessaman. "Ecological energetics and foraging behavior of overwintering bald eagles." Ecological Monographs (1984): 407-428.

Incubation zones: Brinsea Incubation. Check them out for incubators, hatchers, brooders, and information:
http://www.brinsea.com/

Cornhusk Insulation: http://www.newscientist.com/blogs/shortsharpscience/2009/05/insulation-made-from-corn-wins.html

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Did you know?

Some birds incubate eggs by burying them in mounds. Meet the Megapodes! http://en.wikipedia.org/wiki/Megapode

Courtship, copulation, eggs, and other things romantic

Valentine's Day is here and we're all awaiting the first egg in Decorah. Given that the day is a celebration of things romantic, we thought we would discuss copulation, fertilization, and other egg-related subjects.

Courtship

The video below shows Mom expressing interest in Dad. She twists her tail feathers to the side while vocalizing and rubbing against Dad. In Decorah, courtship activities begin in late fall. Mom and Dad bring sticks and branches into the nest, eventually adding soft nesting material as courtship deepens. Food is (often) shared. The eagles vocalize together and spend more time in close proximity, moving from sitting side by side to gently pecking and footing, wing and tail brushing, and body rubbing with tail twisting and vocals. Mom is letting Dad know in no uncertain terms that she is receptive and ready for copulation. A few people have commented on Dad's 'shyness'. While this is pure speculation, female eagles are larger and stronger than males. Perhaps males want to be absolutely certain females are receptive before getting too close.

Video: Mom expresses interest in Dad


Bald eagles and peregrine falcons are both birds of prey, but they have slightly different courtship rituals. In both species, the male brings food gifts and both sexes engage in nest-preparation activities. But peregrine falcons incorporate bowing, and bald eagles don't. The video below shows peregrine bowing, which starts around 28 seconds. We should start to see this courtship behavior sometime in mid to late March.

Video: the male falcon bowing

Copulation

Male eagles, like most male birds, lack an external phallus. Bald eagles mate by touching or pressing cloaca together - the famous 'cloacal kiss'. The female perches and tilts forward, allowing the male to land with his feet lodged on her back. She twists and moves her tail feathers to one side so the mounted male can press and twist his cloacal opening around her cloaca, passing sperm from his cloaca to hers. Intense and rapid vocalizations will precede and accompany their mating. As we’ve seen in Decorah and Fort St. Vrain, mating is brief, intense, and takes place fairly frequently while the eagles are in season.

Video: Eagle copulation at Fort St. Vrain

Eggs!

So we've gone through courtship and copulation. Now the sperm needs to reach the female's ova at the infundibulum, or site of fertilization. The female is regularly ovulating, but sperm needs to be there when an ovum arrives. If sperm are too early, they will die prior to the arrival of an ovum. If sperm are too late, they can't penetrate the eggshell layers that form around the ovum in the female's oviduct. So how can fertilization be assured, assuming both eagles are fertile?

• Copulate regularly. Regular copulation helps assure a good supply of sperm - especially important in an animal that regularly clears its cloaca when eliminating waste!
• Store sperm. Sperm storage tubules maintain sperm viability, prevent stored sperm from being ejected, and continuously release sperm to the infundibulum.
• Concentrate sperm at the infundibulum. Released sperm are passively carried to the infundibulum. Their continuous release and relatively slow drift help ensure that sperm are present when an ovum arrives. 

Let's assume that sperm has reached the infundibulum and found a fertile ovum, yolk erupted, waiting for fertilization. Once a sperm fertilizes the yolk, the outer egg membrane seals off the fertile egg, which prevents further sperm entry. The egg begins to drop through the oviduct, a process that lasts for two or more days. As the egg descends, it is coated in layers: eggshell membranes, cuticle layers, and finally the outer crystallization membranes that form what we think of as the eggshell. Viola - a fertile eagle egg ready for laying and incubation!

Video: An egg's journey

Although we don't know exactly how long egg-laying occurs after mating, it is generally believed that female eagles lay eggs 5-10 days after a successful mating takes place. Since love is clearly in the air at the Decorah nest, we shouldn't have to wait too long.

Have a happy Valentine's Day!

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References

Raptor Research and Management Techniques, 2007
Raptor Research Foundation
Edited by David M Bird and Keith Bildstein
http://www.raptorresearchfoundation.org/publications/techniques-manual

Blog by David Hancock:
http://www.hancockwildlife.org/article.php/EggsEgg-WhenAndHowTheyDevelop

Do Bald Eagles Mate in Flight?

Do bald eagles mate in mid-air? Do bald eagles mate through their feet? We’ve been asked those questions on facebook, via email, and at Ustream.  The short answer? No. Bald eagles do not mate with their feet or during ‘nuptial flight’. They mate by touching cloacae – the cloacal kiss – while perched securely on a tree limb or in the nest. The male mounts the female’s back, twisting his tail under hers. The two press their cloacae together and sperm passes from his cloaca to hers. As we’ve seen in Decorah and Fort St. Vrain, mating is brief, intense, and takes place fairly frequently while the eagles are in season.



Most readers have probably heard of the bald eagle’s whirling nuptial flight. Mates or courting pairs lock talons and whirl through the air, disengaging before they hit the ground. Writers have suggested that this particular courtship activity might prove flight skill, test pair commitment, and/or arouse the eagles to begin mating. While these are lovely ideas, reality is much more complicated. Courting eagles do lock talons and whirl, but so do immature eagles, adult/immature eagles, and adult eagles who (presumably) aren’t courting.
Brett Mandernack, the biologist at Eagle Valley, suggested that immature eagle talon locking and whirling flight might be a precursor to adult courtship behavior.  While some locking and whirling appears to be antagonistic in nature, like the two adult eagles who crash-landed in Duluth in May of 2013 (http://www.usatoday.com/story/news/nation/2013/05/14/eagles-crash-land-minnesota/2159079/), some is not. Brett has watched territorial adults repeatedly lock talons and whirl, separating before hitting the ground and soaring upward to lock talons and whirl again. “Why,” he asked “would mated adults keep locking and whirling if the behavior was solely antagonistic?” Eagles display remarkable plasticity, varying their behavior in response to environmental changes, including the presence of other eagles. Perhaps talon locking and whirling flight can be made to serve a number of purposes, including courtship. Only the eagles know for sure.



We know that eagles who retain a nesting territory and partner are more productive than those that don’t. But to get to that point, an eagle must first settle in a particular area (probably not too far from its own birthplace), establish a nesting territory, and acquire a mate. Soaring displays and vocalization might help an unpaired eagle attract a mate (look at me!) and demonstrate territorial occupation (this is my place!). Talon-locking followed by whirling flight might provide a non-aggressive response to a potential partner, indicating serious interest. If the eagles pair, food gifts and other courtship activities will quickly follow.

In Decorah, courtship activities begin in late fall. Mom and Dad bring sticks and branches into the nest, eventually adding soft nesting material as courtship deepens. Food is (often) shared. The eagles vocalize together, spend more time in close proximity, and gently peck and foot to indicate their interest in one another. In late January or early February, all of this activity will culminate in copulation, with egg-laying beginning roughly 2 weeks later.

Lake Pepin is a great place to watch eagles soar and talon lock. Go the National Eagle Center’s website for more information about eagle watching on the big lake: http://www.nationaleaglecenter.org/

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Sources

Personal Communication, Brett Mandernack

Interactive Behavior among Bald Eagles Wintering in North-Central Missouri
Curtice R. Griffin
The Wilson Bulletin, Vol. 93, No. 2 (Jun., 1981) , pp. 259-264
Published by: Wilson Ornithological Society
Article Stable URL: http://www.jstor.org/stable/4161465

Lifetime Reproductive Success of Bald Eagles in Northern California / Éxito Reproductivo de Haliaeetus leucocephalus en el Norte de California
J. Mark Jenkins and Ronald E. Jackman
The Condor , Vol. 108, No. 3 (Aug., 2006) , pp. 730-735
Published by: University of California Press on behalf of the Cooper Ornithological Society
Article Stable URL: http://www.jstor.org/stable/4151094

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Did you know?

Scientists discover the genetic reason why birds don’t have penises
http://www.smithsonianmag.com/science-nature/scientists-discover-the-genetic-reason-why-birds-dont-have-penises-94130874/
Note: This is a pretty frank discussion that includes a video.