Ornithologi

A studio for bird study

Tag: 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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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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Gyrfalcons in Flight Print: A Gift for the Falcon Enthusiast

by Bryce W. Robinson

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Gyrfalcons in Flight. From left to right, juvenile gray morph, adult gray morph, and adult white morph. 10×20″ Giclee print comprising three Gouache paintings by Bryce W. Robinson. Purchase this print in the store. $40 + shipping and handling.

If you’re looking for a gift for a falcon or raptor lover, or even for the general bird lover, consider this print available in the ornithologi shop. This print details three Gyrfalcons that I painted while working in Alaska in the summer and fall of 2016.