Will Four ever disperse? We've been asked that question via facebook, email, and our forum. Only Four can answer that question, but I thought it might be worth looking back at D1 and D14 for clues.
D1's first flights, 8/01/11 to 8/12/11
The map above shows D1's first flights. She fledged in June, at 81 days of age, and we attached the transmitter to her on July 18, 2011. The maps shows her exploring her natal territory, traveling simple, short back and forth paths as she learns proficient flying, food-finding, and navigational skills.
D14's first flights, 8/01/12 to 8/12/12
D14 was 78 days old when he fledged in late June, He is less centered around the nest and hatchery than D1 was, but his initial exploratory flights are very similar. Like D1, he is flying short, simple back and forth paths as he gains skill and experience.
Four's first flights, 8/01/14 to 8/12/14
Four's fledge occurred at approximately 76 days old, in late June. Like D1 and D14, her early flight pattern is relatively simple - a lot of short back and forth explorations. Her first "loop" occurred on August 10 and was just 1 mile long (.5 miles out and back).
So when does a hatch year eagle stop exploring and start dispersing? D1 was quite obvious. On August 13 2011, she flew north 14 miles toward the Iowa/Minnesota border. By September 6, she was 262 miles north of the nest. She turned south and came back to Decorah, arriving back in NE Iowa on December 24, 2011. Before leaving on August 13, she had never been recorded more than .98 miles from her natal nest.
D1's 2011 dispersal
The map above displays D1's entire dispersal. On August 13, she went from local travel along simple paths to long-distance travel along more complex paths. Her large loop included several smaller loops with fewer of the simple back and forth flights that we saw her first weeks on the wing.
D14's 2012 dispersal
Unlike D1, D14 spent more time flying around the Decorah area and left town twice: once on September 5, for a 24-mile flight south, and once on September 22, for good. So did he disperse on September 5 or September 22? My money is on September 22. D14's movements seem to indicate a higher degree of pre-dispersal restlessness, but he didn't leave permanently until September 22. Like D1, he went from local travel along simple paths to long distance travel that included looping flight. Unfortunately, he died of electrocution on November 6 near Rockford, Iowa. The loss of D14 was tragic for personal and research reasons. Everything we could have learned from him ended in his premature death.
As their flight paths show, D1 and D14 spent some time acquiring skills and strength before dispersing. They needed to be able to fly strongly, work with the wind, find food, and navigate. We have recently begun seeing some increased complexity and distance in Four's flights. Only time will tell if and when she disperses, but Four's flight paths and recent calf-eating excursion seem like good signs. Stay tuned! You can make your own D1, D14, and Four maps here: http://www.raptorresource.org/maps/personal.php
At whatever moment you read these words, day or night, there are birds aloft in the skies of the Western Hemisphere, migrating. If it is spring or fall, the great pivot points of the year, then the continents are swarming with billions of traveling birds... - Living on the Wind: Across the Hemisphere with Migratory Birds We get a lot of questions about migration. Do the Decorah eagles migrate? Do our Peregrine falcons migrate? Where do they go when they leave? We fitted our eagles with tracking devices in part to help answer some of these questions. To date, we've learned D1's migratory paths and summer and winter ranges, observed an interesting difference in dispersal patterns between D1 and D14, and an interesting similarity between D14 and Four. I used to think migration was very simple. Like a lot of people, I thought that all birds except chickadees, pigeons, crows, and woodpeckers migrated once it got cold. They went south to escape snow and ice, returning to nest when the weather warmed up. 'South' was anywhere it didn't snow, or at least didn't snow much: Georgia, the Gulf Coast, South America. I had no idea that many birds don't migrate, or that 'south' could be Minnesota or Wisconsin. Peregrines, Snowy Owls, and Bald eagles taught me otherwise. Among birds, migration is the regular, endogenously controlled, seasonal movement of birds between breeding and non-breeding areas (Salewski and Bruderer 2007). Bald eagles and Peregrine falcons are partial migrators - that is, some members of the species migrate and others don't. This is the most common type of migration, which makes sense since migration is driven by a number of factors, including daylight length, food availability, weather, the time it takes to raise young, and the distance between wintering and breeding grounds. Migration allows exploitation of different habitats as environments change seasonally or successionally (Dingle, 1996). Food availability seems to play a very important role in the migration of Bald eagles: inland northern Bald eagles tend to move southward after ice and snow start putting a lid over their favorite food source - fish, while southern Bald eagles are thought to move northward once warm weather drives fish into deeper water (although there is some debate about this). Weather can also impact migration timing in other ways: for example, a favorable wind pattern might help compel a bird to leave for its wintering or summering grounds if other factors are in place.
D1's looping migratory path in 2012 and 2013
I also thought that birds used to travel the same path backwards and forwards. However, it turns out that many birds, including our own D1, favor loop migrations. This pattern might be a response to seasonal prevailing winds, food availability, tradition, and/or genetic influence. More to the point, loop migrations require more complex navigational skills (and perhaps inheritances) than a simple point A to point B path. So how do birds navigate? Migration studies have found five major methods:
Geographic mapping: When I'm in Minneapolis, I use a number of tall buildings to help me orient the city. It turns out that birds do the same thing, using landforms and geographic features such as rivers, coastlines, and mountain ranges to guide them.
Celestial navigation: migratory birds use the position of the sun (during the day) or the rotation of stars (at night) to orient themselves. Experiments done by Dr. Emlen in 1967 indicate that celestial navigation is learned. http://www.birds.cornell.edu/AllAboutBirds/studying/migration/navigation
Wind patterns: A recent study at Cornell using crowdsourced data found that passerine birds are heavily dependent on wind direction for migration. By shifting routes, birds take advantage of stronger tailwinds in spring and less severe headwinds in fall.
Learned Routes: Some bird species, such as sandhill cranes and snow geese, learn migration routes from their parents and other adult birds in the flock. Once learned, younger birds can travel the route successfully themselves.
What do Bald eagles and Peregrines do? It seems they most likely use multiple sources of information, including celestial and magnetic clues, light polarization, wind patterns and direction, and geographic cues (which would likely be highly correlated with geography). Although parents and young don't migrate together, D1 and D14 were in the company of other eagles every time we saw them, so I suspect that some degree of learning, or at least following, also plays a role. While we haven't yet seen Four in the company of eagles outside her family, she's only begun her wandering. Since young bald eagles are much more nomadic than adult Bald eagles, we hope to have several more years of watching her. In addition to watching our eagles, keep an eye on the animals outside your window. We know fall is here, and so do they.
Birds may begin gathering in huge premigratory flocks, gorging on food to build fat reserves, and exhibiting restlessness, also known by the marvelous word zugunruhe. These behaviors help prepare birds for migration. Keeping a well-stocked bird feeder helps them too.
Juvenile peregrine falcons are on the move! You'll sometimes catch a stranger on cam as they disperse down river. Please let us know if you get any band numbers!
Frogs and turtles may begin migrating from summering breeding grounds to deeper bodies of water. While their travels are short, they still fit the definition of migration. For more on frog hibernation, click here. The Minnesota DNR has a very good article on helping migrating turtles cross roads, some cities close roads, and volunteers help keep migrating frogs safe.
Some insects migrate and others hibernate. Aggregating paper wasps may be getting ready to hibernate, while dragonflies migrate in large numbers (or check this source out).
Watch out for migrating Mule deer! According to National Geographic, they make a 150-mile migration twice yearly from the low desert to the high mountains.
Have a happy fall and take the time to watch for migrating birds and other animals! Would you like to know if the winds are favorable for bird migration in your area? Check these links out:
Lissajous patterns. It struck me that the eagles' loop travels somewhat resembled a Lissajous pattern. A little googling found this very cool project: http://kaurov.com/wordpress/?p=692
* Regarding male Peregrine dispersal: of course, there are exceptions. We released Zeus, the male at Woodman Tower in Nebraska, in Rochester New York. We were very surprised when he showed up in Nebraska. Did he fly west intentionally or was he some how blown off course or lost?
From our friends at Minnesota Power. Thanks for sharing!
Amy and Matt
The three chicks at Hibbard Renewable Energy Center now have names as well as leg bands.
The youngsters, two females and a male, are Spike, Jolt and Surge. The Hibbard falcon names were dreamed up by Jodi Piekarski, supervisor, generation production at Boswell. She submitted the names Spike, Jolt and Surge, and employees selected the three as winners in a Powergram online contest that attracted a total of 170 electronic votes.
The votes were tallied today, the same day that Bob Anderson and Amy Ries of the Raptor Resource Project were in town to band the chicks born about four weeks ago. Earlier in the day, they also banded the chick born at Greysolon Plaza in downtown Duluth.
Ries, along with Minnesota Power employees Doug Braff and Matt Pohl, climbed the stack at Hibbard as the youngsters’ parents circled and screeched in alarm and news crews from WDIO, KBJR and Fox television stations watched from the roof and documented the climbers’ progress. The nesting box is on a platform on the stack about 200 feet above the ground.
Doug Braff and friend
It was a climb that only a short while earlier was in jeopardy. The MP safety crew—John Hollingsworth, Ian Wenzel and Dan Belluzzo—were checking weather conditions and monitoring lightning strikes. Fortunately, a storm that had been moving closer to Hibbard dissipated and banders were given the go-ahead.
It was Pohl’s first time as part of the banding team. He said he volunteered to help because “I figured it was a unique opportunity.” He said he rarely has climbed anything higher than the roof of his home and Tuesday’s climb “wasn’t as scary as I was expecting.”
Braff, who supports Minnesota Power’s Falcon Cams and is a veteran falcon bander, described the chicks as “feisty,” the conditions as “nice and breezy” and said the experience was “wonderful, as usual.”
Ries checked the chicks for any signs of disease or parasites and placed the bands around their legs. The bands help researchers study the movement and habits of the birds. “They look great,” Ries said as she removed her climbing and safety gear after the climb. “They’re just really nice looking falcons.”
One egg at Hibbard and the four eggs at Boswell Energy Center failed to hatch this spring, and Anderson attributes that to cold temperatures at a critical time. It was a theme the Raptor Resource Project, based in Decorah, Iowa, has seen play out at many falcon nests in the Midwest this year.
Still, even with no luck this year, Boswell is one of the most productive of the Midwest power plant sites, he said. More than 60 peregrine chicks have hatched at Boswell since 1993 and 15 chicks have been banded at Hibbard since 2008.
Contest details
Piekarski’s names received 73 of the votes cast by employees, or 42.9 percent of the ballots. Finishing second in the voting was the trio of Louie, Copper and Ace. The names Aspen, Spruce and Birch finished third in the voting. Breezzy, Chillee and Bhurrrrr captured fourth place (and last in spelling).
In her naming submission, Piekarski said her electricity-based falcon names were tied to the speed of the peregrine falcon: Spike being “a sudden increase in the amount of electricity that a system produces;” Jolt signifying “a sudden strong increase in energy;” and Surge “a sudden increase in electrical power that can damage equipment connected to it.”
For her winning entry, Powergram will present Piekarski with a beautiful 8-by-10-inch peregrine falcon print.
Yesterday at about 10:45, Decorah fledgling EWOT was
electrocuted on a high voltage power line roughly ½ mile from the mulch pile
that both fledglings have been spending most of their time on. It was reported
to us late in the afternoon. We collected and examined him, returning to the
site of the electrocution to gather more information once that was done. Here
is what we know.
The line was a 96 Kilovolt transmission line owned by ITC Holdings (http://www.itc-holdings.com/). In
general, electrical delivery can be divided into two types: transmission and
distribution. High-voltage transmission lines carry electricity over long
distances from power plants or grids to substations. The poles or towers are
physically larger and taller than those that support lower-voltage distribution
lines and don’t support anything except electrical lines. Distribution lines carry
electricity from substations to consumers and are supported by what most of us
probably think of as utility or power poles. Utility poles are often made of
wood and, unlike transmission lines, may also carry telephone and cable wires
or support street lights.
ITC is able to detect fluctuations and other anomalies on
their lines. When they sensed an anomaly, they sent a field technician out to investigate.
He found and collected EWOT, and turned him over to the Iowa Department of
Natural Resources. They saw the transmitter and called Bob to let him know that
an eaglet had been electrocuted.
When we first got word of another electrocuted eaglet, we
assumed it had contacted a standard utility pole. According to Refining Estimates of Bird Collision and
Electrocution Mortality at Power Lines in the United States, electrocutions
occur primarily at distribution lines, while collisions occur at both
distribution and transmission lines. That’s certainly been our experience,
since every eagle we’ve picked up has been found at the base of a distribution
line. I pictured a standard wooden utility pole as we glumly drove over for our
field investigation. I was surprised to instead find a high-power line between
a field and a hill. We hiked out and took a look at the scene. We weren’t able
to find scorch or singe marks on the pole or insulators, and the eaglet’s body
was not at the base of the pole, as we’ve seen elsewhere, but under the lines
three to four feet from the pole.
An examination of the eaglet’s body revealed singeing and
burning around his elbow and feet. Electrocution can’t happen unless a bird’s
body creates a circuit between ground and voltage, or different voltage phases,
allowing energy to flow from high to low. Sitting on a wire won’t harm a bird,
since it doesn’t create a circuit. But he closed a circuit with his wing and
one foot, creating the flow that killed him.
In addition to singeing, the eaglet’s wing had extensive
tissue damage and some severing. Although it seemed unlikely, we needed to know
whether the transmitter had somehow created or closed the circuit that led to his
electrocution. A quick look at the transmitter showed no damage, scorching, or
discoloring. We cut the straps and removed it from EWOT’s body. The straps were
intact and there was no scorching, singeing, or burning under the straps or
backpack pad. Finally, we made sure the receiver could detect the transmitter. The
transmitter was functioning normally, so we concluded it hadn’t been part of our
eaglet’s electrocution.
Bob contacted ITC this morning. The biologist he spoke with
told him that they hadn’t seen an electrocution on a high kilovolt line in the
three years he’d worked for ITC. Having said that, they reported the
electrocution to the U.S. Fish and Wildlife Service and the Avian Power Line
Interaction Committee, and they are assessing steps that can be taken to
prevent another electrocution or collision.
What we think
The pole was up to code and we haven’t had any problems at a
transmission line before, so we suspect the electrocution was a terrible accident.
Other electrocutions and near-misses in Decorah involved distribution poles
with wonderful perching spots near the hatchery, where the eagles regularly
hunt, fly, and hang out. The
transmission pole provides a bad perching spot overlooking a poor hunting
ground bordered by trees. Although electrocution was clearly the cause of death,
we suspect that EWOT might have collided with a wire and dropped, contacting
other wires or the pole before dropping to the ground. Death was very quick.
Where do we go from here?
We don’t know whether ITC will install diverters or a
similar non-collision technology over one death. Companies tend to set
priorities based in large part on collisions, electrocutions, and known
migration/movement paths. Reporting is key and we are very glad the company
didn’t choose to sweep the electrocution under the rug.
Bob talked to ITC this morning. If there are any more
deaths, the company will report them to us, the DNR, and the USFWS. Neither D1, D14, or Four have spent any time near
the high voltage line, but if Four or D1 start hanging out, we’ll make ITC and
everyone else aware of it.
Why can’t you build safe perches?
Alliant Energy, the D12 Memorial Group, the Decorah High
School, and Decorah Building supply were able to make the distribution poles at
the hatchery safer through insulation and safe perches. However, we’re not sure
this was a perching problem and we can’t encourage perching on high voltage
transmission lines since they are too dangerous. If protection is installed, it
will probably be in the form of diverters that make it easy for birds,
including eagles, to see the power lines.
What can we do?
Our wonderful fans want to know what they can do to make
power lines safe. A few suggestions:
·Does your power company have an Avian Protection
Plan? Click here for more information: http://www.aplic.org/APPs.php.
Birds aren’t the only issue, either – my electrical cooperative is upgrading
equipment because of squirrels! Talk to your company and find out what they
have in place.
·Report electrocuted animals to your power
company and wildlife agency. If your power company shrugs it off, document the
problem and talk to your state’s regulatory agency. It’s my experience that
most utility companies are very responsive to electrocutions. They kill
animals, destroy equipment, can start fires, and are expensive.
·Learn more about the issue. A few good places to
start:
While we can’t protect transmission lines with safe perches,
most of our electrocutions have been on distribution lines. This seems like a
good time to share the story of the D12 Memorial Group’s work with making
distribution poles safer.
We are really dismayed by the electrocution of another eagle
but believe we can do better in the future. We’ll continue working with power
companies to improve outcomes for birds of prey and we’ll certainly let you
know what happens here. In the meantime, please feel free to share your stories
of improvement and recovery with us.
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!
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
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].
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.
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.
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.
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:
Bob Anderson, who made me aware of the role hormones play in bird reproduction. He could write a book on the subject.
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
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 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!]
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.
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
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:
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.
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:
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.
