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.

Friday, March 28, 2014

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: 

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!

Monday, March 24, 2014

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 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 We anticipate hatch in Wilma's nest at the end of March or very early in April. 


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:

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.

Tuesday, March 18, 2014

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. 


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:

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:

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:

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:

Monday, March 10, 2014

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:

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 to see them! Again, we are anticipating goose hatch some time between March 27 and March 31.


Stanford University, Altricial and Precocial:

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:

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:

Developmental Modes and Developmental Mechanisms can Channel Brain Evolution