Wednesday, April 30, 2014

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.

Things that helped me write this post:

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.

Tuesday, April 22, 2014

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: 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:
  • 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':
  • 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!]

Saturday, April 12, 2014

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!]

Thursday, April 03, 2014

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:

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.

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

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.

Things that helped me learn and write about this subject:

Wednesday, April 02, 2014

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:
Gosling leg stretch – Eaglewhisperer18:
Wilma’s little goslings – Mocha Mama:
The Jump! – Mocha Mama:
Waddle to the pond – Mocha Mama:
Goslings swim - MsDebbiB:

To learn more about incubation and heat/cold damage, follow this link:

To learn more about the differences between altricial and precoccial birds, click here:

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

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

#DecorahEagles #RaptorResource

Tuesday, April 01, 2014

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 Click the 'Fort St. Vrain Eagles' link to view.