Sunday, February 21, 2016

Is N2B big enough? Where are Mom and Dad? Answers to your questions!

Is N2B big enough?
This is probably the number one question we've fielded this week. A lot of people have expressed concerns that N2B isn't big enough for the eagles. However, the nest was already roughly 4.5 feet high by 5 feet wide when we left it in August - big enough for Neil to sit comfortably inside it! The eagles have built it up substantially since then, as the image below shows.

Image courtesy Sherri Elliott. The red line by Neil's head shows the location of the
diamond shaped bark on August 20th.
So why does the nest look small to us? Camera angles can easily fool the eye. The nest is foreshortened by the angle of our camera and appears smaller than it actually is. Wikipedia defines foreshortening as "The visual effect or optical illusion that causes an object or distance to appear shorter (or smaller) than it actually is because it is angled toward the viewer."  The nest is also not scaled evenly, further distorting its true size and shape.  If you would like to take a look at more perspective illusions, follow this link: You might be surprised at how easy it is to fool the eye!

Is the nest smaller than N1 and N2? It could be...but remember, we haven't seen a nest in year zero before. We watched N2 from the ground in 2012/2013 courtesy Jim Womeldorf, and we didn't film live from N1 until its third year. We don't really have an adequate basis for a first-year comparison.

Is the nest too small? Mom is about three feet long, while slightly smaller Dad is about 2.5 to 2.6 feet long. Both of them are able to comfortably fit into the nest and incubate eggs, even if they can't back their tails up to the tree limb. The nest has plenty of room now and it should only get bigger as they haul in more branches and grasses. Nest work is never done!

Why didn't Mom and Dad put the egg cup in the center of the nest?
We can only speculate about the location they chose, but we suspect that the tree limb provides them with some protection from wind, weather, and bright sunlight. If Mom and Dad sit between the eaglets and the rails, as we think they will do, the eaglets will have a lot of room when they begin to explore the nest. Looking at the nest cup now - that not-so little egg nestled in a deep pile of fluffy grass - I think they couldn't have done a better job building it.

Why are Mom and Dad spending so much time off the egg?
This has dovetailed with another question: do eagles delay incubation? Peregrine falcons don't begin full incubation until after the third egg is laid in a four-egg clutch, but bald eagles begin incubating immediately because they usually lay eggs (at least in this part of the country) in weather at or well-below freezing. If they didn't incubate, the eggs would freeze and die. It's pretty well-accepted that bald eagles don't delay incubation because they can't.

Having said that, the weather is extremely warm this year and egg number one is still very early in embryonic development. Mom and Dad don't need to incubate it constantly to keep it from freezing and Mom may not yet be deep in what Bob used to call the 'incubation doldrums'. Eagles are relatively intelligent birds with very plastic behaviors, so it makes sense that they might spend less time on a newly-laid first egg in warm weather, even if they don't delay incubation like peregrine falcons do. Remember, eggs have optimum incubation temps (about 99 degrees for an eagle egg) and humidity. Mom and Dad control temperature and humidity by getting on or off the eggs as needed, and they haven't lost one yet.

It also helps to know that 2014 and 2015 were both much colder and snowier than 2016 (knock on wood). In 2014, Mom laid her second egg in wind chills reaching -50F and we really didn't see much of the eggs that year at all! While eagles are well-adapted to cold weather, I hope it stays on the warmer side this spring.

When will the next egg or eggs be laid?
If history is any guide, Mom will lay the next egg this afternoon or evening (February 21), and the third, if there is one, might come on Thursday, February 25.  Despite what we see in Decorah and at Fort St. Vrain, three-egg clutches aren't especially common. The breakdown looks like this, although the study cautions that results could change over time:
  • 79% of clutches have two eggs
  • 17% of clutches have one egg
  • 4% of clutches have three eggs
When will the eggs start to hatch?
Bald eagle eggs hatch 35-37 days after they are laid, so hatch could start as early as March 25. However, I'm going to go with a longer forecast given that the first egg started hatch last year on March 27! Look for Mom and Dad to start vocalizing and chirping at the eggs as they go through the process of hatching. Altricial birds hatch blind, so vocalizing is an important part of the filial imprinting process - and a lovely thing to hear!

Read this blog for more information on embryonic development and hatching: At roughly 63 hours from lay time, D24's legs should be beginning to form.

Bonus spectrogram
Mom chirps as she lays the egg. I'm not real happy with this spectrogram because there was
a lot of noise versus signal, but her soft chirps can still be seen.

Wednesday, February 17, 2016

First Egg of 2016 for Fort St. Vrain Eagles

Congratulations to the Fort St. Vrain bald eagles on their first egg of 2016! The egg was laid last night around 9:22pm Mountain Time. This marks the 31st egg laid since we began keeping track in 2003!

What does the Fort St. Vrain site look like? The nest (FSV-N0) is located in a cottonwood on the banks of the St. Vrain River near Platteville, CO, on property owned by Xcel Energy.  We’re not sure how old it is, but Bob Anderson and Rob MacIntyre put the first cam system up in 2003, when the nest was already well established. FSV-N0 is built primarily of cottonwood branches (the dominant tree in many river systems out west) and lined with prairie grass.

As the eagles look out of their nest, they might view the foothills of the Rocky Mountains, roughly 15 miles west of the nest, or the junction of the St. Vrain and south Platte rivers roughly 2 miles north. The land can be broadly characterized as sweeping and open – beautiful, but very different from the folded hills and forests of Decorah and Eagle Valley. Primary food sources include the river systems (fish and turtles) and a nearby prairie dog colony that was just re-established after serious flooding two years ago.

While a two-egg clutch is more common among bald eagles, the Fort St. Vrain pair has (like Decorah) tended to lay three eggs. We can expect the eagles to begin incubating immediately to prevent their eggs from freezing. However, if the weather is relatively warm, we may see them spend a surprising amount of time off the eggs. Eggs need both an appropriate temperature (around 99 degrees) and appropriate humidity, so Mom and Dad will get up and down as necessary to control them. Adult eagles have body temperatures of 104 to 105 degrees, so they have heat to spare when it comes to incubation. Eagle eggs hatch roughly 35 to 37 days after they are laid – so we are hoping for eaglets around March 19th at Fort St. Vrain!

The Fort St. Vrain nest can be watched live at Xcel Energy’s site at or on our site at Both cams can be watched at the same time here:

Wednesday, February 10, 2016

We are Eggs-pecting!

Sherri Elliott got some great vocals and video this morning at Ustream! After a few beaky 'kisses', Mom and Dad were heard copulating not far from the nest. While we don't have recorded video from Fort St. Vrain, the eagles there have been copulating as well. It looks like eggs are on the way in both places! Ustream highlight: We'll add a youtube video as soon as we have one for those of you on devices.

While we don't know when the eagles are going to lay eggs, we are entering the time period in which laying has historically started. In Decorah, the first egg has been laid as follows:

  • February 18, 2015 - first egg in 2015
  • February 23, 2014 - first egg in 2014
  • February 17, 2012 - first egg in 2012
  • February 23, 2011 - first egg in 2011

Note that 2011 and 2014 were very similar. All three eggs were laid on the same date those two years. 2012 and 2015 were both a little milder than 2014 (the Winter that Wouldn't Die) and Mom was just beginning to lay eggs in 2011. Personally, I'm thinking sooner rather than later...but even February 23 is just thirteen days away. While it is rare for bald eagles to lay three eggs, Mom has a history of doing just that! The breakdown is as follows:

  • 79% of clutches have two eggs
  • 17% of clutches have one egg
  • 4% of clutches have three eggs

In Fort St. Vrain, the first egg has been laid as follows:

  • February 14, 2015 - a first Valentine's day egg for 2015!
  • February 21, 2014 - first egg in 2014
  • February 17, 2013 - first egg in 2013
  • February 16, 2012 - first egg in 2012
  • February 16, 2011 - first egg in 2011

Although Fort St. Vrain is about 714 miles from Decorah as the bald eagle flies, the two sites have very similar nesting chronologies, with the Fort St. Vrain eagles usually leading Decorah by a few days and both females tending to lay three eggs. This is an interesting contrast with the Eagle Valley site, which is only about 50 miles from Decorah but was roughly a month behind the year our cammed nest was active. The female there only laid two eggs.

So what can we expect once the first egg is laid? The eagles will begin incubating immediately to prevent it from freezing. However, if the weather is relatively warm, we may see them spend a surprising amount of time off the eggs. Eggs need both an appropriate temperature (around 99 degrees) and appropriate humidity, so Mom and Dad will get up and down as necessary to control them. Adult eagles have body temperatures of 104 to 105 degrees, so they have heat to spare when it comes to incubation. We can expect the eggs to hatch in both places roughly 35 to 37 days after they are laid. If the past is anything to go by, the Moms will spend more time incubating than the Dads, although the division of labor varies from nest to nest.

Eagles are well-prepared to handle snow and cold, but weather has sometimes been an issue at the Fort St. Vrain site. While Fort St. Vrain is slightly warmer than Decorah in March (26-53F versus 25-46F), it gets an average of ten to eleven inches of snow as compared to Decorah's five and a half. Wet, heavy snow can provide a serious challenge to eaglets not old enough to thermoregulate, although the re-establishment of a prairie dog colony not far from the Fort St. Vrain nest means that hunting can be done a little closer to home.

We wish all of the eagle families well and are very much looking forward to the coming season! Bob would be so pleased with the success of N2B and our new camera systems! I'd like to think he approves.

Saturday, February 06, 2016

Philippine Eagle Puppet Feeding

How do we learn to become human? From fellow humans, of course! We are raised by humans, fed and cared for by humans, and taught language by humans. Parents, relatives, friends, teachers, and other people around us teach us language, cultural norms and values, and the ins and outs of social interaction. From them, we learn the information and skills we need to function as members of our society at any given time in our lives. As we grow, we gain companions, friends, enemies, co-workers, rivals, and perhaps mates who will shape our lives and help us raise the next generation of children to instill with our cultural norms and values. 

The same is true of animals. Peregrine falcon and bald eagle parents spend a lot of time interacting with their young: brooding them before they old enough to thermoregulate, stuffing them with food at every opportunity, vocalizing (think of a peregrine falcon chupping encouragingly at a hatchling), and playing post-fledging chase and hunt games in the first few weeks of flight development. Birds learn to be birds from other birds: the vocalizations, songs, or calls of their species, flight skills (think of fledgling peregrine falcons chasing one another, or a flighted predator chasing down flighted prey) and, among birds that are social, the intricacies of social interaction. As they grow, they learn how to acquire food, avoid danger, find mates, and raise the next generation of young. 

In birds and mammals, this process starts with imprinting, defined as "Rapid learning that occurs during a brief receptive period, typically soon after birth or hatching, that establishes a long-lasting behavioral response to a specific individual or object, as attachment to parent, offspring, or site". In short, we first recognize our parents, which lays the groundwork needed for us to recognize and interact with our species and eventually find mates. This type of imprinting is referred to as "filial imprinting". 

But what happens when a human is responsible for raising a bird? If humans are a bird's only role models and source of food or protection, than it will imprint on humans for species recognition. As a sexually mature adult, it will reject its own species and seek the attention of humans. People raising birds for release in the wild take steps to prevent human imprinting from happening, including foster-parenting and puppet-feeding.

When Bob was raising falcons for release, he turned young birds over to a female 'foster-falcon' at around 10 to 12 days of age. By feeding and caring for them, "Freddy" imprinted the young falcons with a falcon model. As juveniles and adults, they sought a bond with their own kind rather than with us.
Philippine Eaglet feeding. Photo by Kike Arnal.
However, foster parenting isn't always an option, especially among critically endangered birds. Kike's photo shows Philippine Eagle Center staff puppet-feeding a Philippine eagle nestling. The person behind the mask imitates a Philippine Eagle parent: vocalizing, interacting with the eyass, feeding it, and providing protection. The eaglet's room is painted to look like the forest it will eventually live in and contains the sounds that will surround it as an adult. These steps imprint the young eaglet on a Philippine Eagle model, establishing a behavioral response to other eagles and forest habitat, rather than human beings and an urban habitat. The puppet is our way to teach a Philippine eagle that it is an eagle, not a human.

Imprinting is a fascinating topic and we'll write more about it later this year. There is a reason that adult eagles chirp to hatching eggs! 

Things that helped me learn and write about this topic:

Learn more about the "Father of imprinting", Konrad Zacharias Lorenz. 

Monday, February 01, 2016

Sounds of the Eagles

I just finished the book Birdsong by Don Stap, a book which seeks to answer the question Why do birds sing and what do their songs mean? Most studies of bird song have been done on oscine birds, which are a subset of passeriformes with a complex voicebox. Many oscine birds such as chestnut-sided warbler, brown thrashers, hermit thrushes, and starlings sing complex sounds that might include, depending on the bird, buzzing, clicking, trilling, and warbling. Non-oscine birds like bald eagles (an accipitriform) might fascinate us with their striking colors, amazing flights, and sheer size, but their vocalizations don't tend to overwhelm us with their beauty or musicality.

After reading Birdsong, I decided to download some spectrogram software and run a few eagle vocalizations through it. The software I chose was Praat, a powerful free acoustical analysis program available from the University of Amsterdam. I wanted to see how 'questionable' copulatory vocals (are they mating?) appeared next to known copulatory vocals (they are mating!).

This was the sort of thing I tended to see. Copulation followed a pretty clear pattern, and Dad also tends to have a higher voice than Mom as shown by the sonograms above. 'Was that copulation?' is Mom alone and was not, in fact, copulation: the bars are low (signaling Mom's deeper voice), thick, and pretty distinct. 'That was copulation!' starts with a brief vocal by Mom at left, and continues into Dad's copulatory vocals - high, quick, and a little complex.

Did all eagle vocals look somewhat like copulation? While Dad's copulatory vocals tend to have a unique sound (I listen for a little warble or chirp and count to seven), eagles don't have complex voiceboxes, and the top vocal isn't that different from the bottom vocal. I decided to compare known non-copulatory vocals next.

Look at 'Mom with a Fish'. It was a cool sounding vocalization and doesn't really look much like copulation. If anything, her initial vocalizations look a lot like Dad's in the 'Sound a Warning' spectrogram , although they are lower. She was mantling a fish after what sounded like a couple of warning vocalizations before she came to the nest, and concentrated energy in high and low pitches, just like Dad did with his initial warning to an unknown neighborhood intruder. The second part of 'Sound a Warning' features Mom and Dad rapidly vocalizing together. While this somewhat resembles the 'solicitation' spectrogram, the vocal pulses are a little farther apart and higher. Personally, I think that 'Mom solicits Dad' most closely resembles copulation. Is she vocalizing the 'music of love' to indicate receptivity? Note that the unknown noise in the spectrogram figure prior to this one really closely resembles her solicitation.

Of course, I also had to compare known copulations. Keep in mind that we used different microphones in 2012 than we do now, and they were located in a slightly different position relative to the nest.

Even given the changes since 2012, these spectrograms look quite similar! It appears that copulatory vocalizations are quite distinct, and spectrograms could be used to help determine whether those early to mid-January vocals are copulatory in nature. After all, we can't always see what Mom and Dad are doing in the upper branches!

While this was more of a thought experiment than anything else, it looks like bald eagles have a little more to say than we realize, even if they aren't singing when they do it. I am looking forward to recording their interactions with eaglets later this year.

I am not a sound recordist. I am sure these spectrograms would benefit from professional equipment, but I have a 64-bit ASUS PC laptop with no special audio equipment whatsoever. The spectrograms were made recording youtube videos via praat in the quietest room of my house, with no one home except myself and two dogs. They were taken from the following videos (note: I can't find the 'was that copulation?' from 2016):

Praat audio software: