Ornithologi

A studio for bird study

Category: gyrfalcon

Published in the Journal of Raptor Research: Dietary Plasticity in a Specialist Predator, the Gyrfalcon (Falco rusticolus): New Insights into Diet During Brood Rearing

by Bryce W. Robinson

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I’m privileged to once again see a painting of mine don the cover of the Raptor Research Foundation’s quarterly publication, the Journal of Raptor Research. This time, however, is more special since the painting of a Gyrfalcon carrying its prey, an Arctic ground squirrel, corresponds to the feature article authored by myself and Travis Booms, Marc Bechard, and David L. Anderson.

Our publication titled “Dietary Plasticity in a Specialist Predator, the Gyrfalcon (Falco rusticolus): New Insights into Diet During Brood Rearing” details patterns we documented through implementation of nest cameras in 20 Gyrfalcon nests in 2014 and 2015. The largest camera study of nesting Gyrfalcons provided us with many new insights into the biology of this species, some of which we have already published, some that we have not. In this publication, we document a previously undescribed shift in prey use throughout the nestling period, from a diet of mostly Ptarmigan early in the season, to squirrel in the late season. This shift to squirrel is an important consideration on many levels. It highlights the nuances to Gyrfalcon prey use in Alaska, and the potential importance of squirrels in the later season for juvenile success and development. The apparent importance of squirrels also has implications for understanding ecosystem changes and how shifts in prey landscapes may impact Gyrfalcon reproduction. The stage is set to explore further.

Below are a few photos that describe the work that went into producing this publication. These highlight a some of the >750,000 nest camera images we collected from which the diet was quantified, as well as photos of the field work, and the people that made this effort possible. 

You can read our paper in the Journal of Raptor Research here:

https://bioone.org/journals/journal-of-raptor-research/volume-53/issue-2/JRR-15-58/Dietary-Plasticity-in-a-Specialist-Predator-the-Gyrfalcon-Falco-rusticolus/10.3356/JRR-15-58.full

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A female Gyrfalcon feeds nestlings. Image copyright Bryce W. Robinson/The Peregrine Fund.

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A female Gyrfalcon feeds her newly hatched nestling, alongside hatching eggs. Image copyright Bryce W. Robinson/The Peregrine Fund.

Female Gyrfalcon feeds nestlings Arctic ground squirrel

Female Gyrfalcon delivers an Arctic ground squirrel to nestlings. Image copyright Bryce W. Robinson/The Peregrine Fund.

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A female Gyrfalcon stands alongside c. 14 day old nestlings. Image copyright Bryce W. Robinson/ The Peregrine Fund.

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Parental care photo 1. A female (left) broods newly hatched young, reluctant to leave the nest at the male’s (right) arrival. Every Gyrfalcon would occasionally look at the camera, as seen here, but were otherwise unaffected by its presence. Image copyright Bryce W. Robinson/The Peregrine Fund.

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Parental care photo 2. In some cases, males were keen to participate in brooding and feeding young, as is shown here. In even fewer cases, the females were tolerant of this behavior. Image copyright Bryce W. Robinson/The Peregrine Fund.

Bryce and Gyrfalcon nest camera

Bryce W. Robinson sights in a nest camera at a Gyrfalcon nest. Image by Caitlin M. Davis.

Bryce rappelling into Gyrfalcon nest

Bryce W. Robinson rappelling into a Gyrfalcon nest in western Alaska. Image by Neil Paprocki.

Special thanks to the following people that made the field work happen

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John Earthman and Tinsel

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Neil Paprocki

Ellen in Gyrfalcon nest with nestling

Ellen Whittle holding a Gyrfalcon nestling in 2015.

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Mark Jeter and Ellen Whittle against an Alaskan landscape in 2015.

Special thanks to the institutions that made this work possible: Boise State University, Alaska Department of Fish and Game, and The Peregrine Fund

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Remembering Tom Cade: 1928-2019

by Bryce W. Robinson

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Showing Tom Cade an occupied Gyrfalcon nest with a nest camera, recording images for The Peregrine Fund’s Gyrfalcon Conservation Program.

Today I’m remembering Tom Cade, ornithologist and conservation giant. Tom passed away yesterday at the age of 91. His legacy is widespread, not only across the earth but through time, for generations into the future. Rather than describe this enduring legacy, I want to here describe one of my most cherished memories of spending time in the field with Tom as I showed him my study area during my Gyrfalcon work.

While I was conducting my field study on nesting Gyrfalcons in western Alaska, Tom came to visit for a few weeks. He stayed with me and Ellen Whittle, my field partner, in a small apartment in Nome. It’s hard to describe the conditions in such an apartment, but the few photos I’ve included here should be telling. I was so impressed with Tom, since he seemed entirely content to be in this run down shack of an apartment, cramped with two young ambitious biologists. In fact, I think he enjoyed it!

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Tom Cade and Travis Booms, walking along a tundra road on the Seward Peninsula.

Of course, we only spent time indoors when the rain wouldn’t allow otherwise. We made many trips out into the tundra to show Tom around, and Tom also spent time with Travis Booms and Joe Eisaguirre as they flew around the peninsula in a helicopter, accessing Gyrfalcon nesting sites. As we drove the roads with Tom, looking for wildlife and checking on raptor nests, we listened intently as Tom told stories of his last visit to the region nearly 60 years prior. He told us stories of a mid-tundra train wreck, seeing his first Gyrfalcon, and how the Nome area truly was different from his last visit, with more vegetation than he had previously recalled.

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Tom Cade, a man with an incredible legacy and an excellent sense of humor.

Apart from his unending wisdom and knowledge, I was impressed with Tom’s sense of humor. He was having fun, and wasn’t afraid to let it show. As is appropriate in western Alaska, July is a time for King Crab. With Tom in town, we had a great excuse to occupy our time during bouts of rainy weather with Crab feasts! I’ll never forget having crab with such excellent people, and I could tell from the photo above that Tom was having a great time as well.

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Crab Feast! Tom Cade, Bryce Robinson, Ellen Whittle, and Joe Eisaguirre. I think Joe was hitting his limit at this point. Photo courtesy of Travis Booms.

After Tom departed Nome and returned to his home in Boise, and I came home following the field season, we saw each other only intermittently. The last time I saw Tom Cade was in a meeting, only a few months ago. He listened, and only spoke when he needed to. But, he was participating. His passion was enduring, so much so that even until the last parts of his extraordinary life, he participated in the work he had set forth.

It is sad to see people go, but it provides us all a perspective on our lives, how we choose to live them, and who we are and want to be. Reflecting on Tom’s life has caused me to reflect on myself, and how I might honor and continue what the man did for multiple species facing extinction, and for the people he inspired, inspires and will inspire. I’ll take that spirit into the future, and do with it what I can.

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Generations of Gyrfalcon researchers: Bryce Robinson, David L. Anderson, Tom Cade, Travis Booms, and Mike Henderson.

If you’re unfamiliar with the legacy of Tom Cade, visit The Peregrine Fund’s website. Everything you see there is a testament to Tom’s legacy, and what he created. Also visit the following link for a great video highlighting Tom’s life: https://www.peregrinefund.org/people/cade-tom

Differentiating Adult and Juvenile Gyrfalcon (Falco rusticolus)

by Bryce W. Robinson

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Given that much of my career has been focused on the world’s largest falcon, the Gyrfalcon, I often get questions about their life history and Identification. A recurring question is the age of individuals that are observed in winter. Most often, folks ask about juvenile vs. adult, so I decided to make available a simple illustration with annotations as a reference for those with these questions.

What I’ve realized is that fleshy parts confuse a lot of people, since an adult should have yellow legs and cere, whereas a juvenile should have blue. However, it takes female birds much longer to change (well into their second year), and the coloration is also influenced by individual quality and hormones. Some adults, particularly females, tend to be quite dull in the winter (compare this with observations of gull legs in winter, e.g. California Gull). Adults that are likely three years or older (given presence of retained feathers in the upper wing, etc.) can have surprisingly dull legs that may appear blue under certain conditions. The key then is to take a step back and focus on the plumage, since in most cases it is quite straight forward.

The illustration above aims to highlight the key points for aging a Gyrfalcon between adult and juvenile. Eventually I’d like to visually describe more micro-aging factors, but for now I think this will be a helpful resource for those more unfamiliar with this species.

Please, feel free to send me feedback and suggestions. Constructive criticism is always welcome.

Gyrfalcon (Falco rusticolus) Plate

by Bryce W. Robinson

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My friend Kenneth, a Gyrfalcon researcher in Norway, is perhaps the most enthusiastically obsessed Gyrfalcon lover I know. I really appreciate his passion for the bird. Next week he is traveling to Salt Lake City for the Raptor Research Foundation’s annual conference. He asked me to paint a Gyrfalcon portrait for him, so I decided to take the opportunity to illustrate some perched birds to populate the plate I’ve been putting together. I going to produce some giclee prints of this plate, but I’m limiting it to 20 prints. If you like this image, and would like to purchase a print, it is available in the shop!

It’s taken me some time to paint birds that I’m pleased with enough to put into plate form. I’m still a bit at odds with these birds, but I think the above image best fits what I’m going for in creating the plate. My next step will be to paint some different postures and explore which best fills the gap in understanding the different positions and appearances that a Gyrfalcon may take on, in varying conditions. Additionally, the plate needs multiple different in flight postures, and some other age and plumage morph descriptions. Progress has been made either way, and I’m excited!

Below is the painting that I did for Kenneth, as it will look to him. I’ll be traveling to Salt Lake City myself, with this painting alongside me. Thanks for the opportunity Kenneth!

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