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Thread: Winter Ptarmigan Diets and Competition

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    Member PG13's Avatar
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    Default Winter Ptarmigan Diets and Competition

    Something to "chew" on for 2012...

    I thought I would start this thread as an outlet for our ptarmigan mixing discussion from the Merry Christmas thread. Alaska's three ptarmigan species often occur in the same area (called sympatry) during the winter when food availability chases white-tailed and rock ptarmigan into the haunts of the big willow ptarmigan. I have attached two papers from decades ago written by what could probably be considered the top two ptarmigan scientists Alaska has ever hosted. The Roberts, Weeden and Moss, were pioneers in their investigation of ptarmigan in the 60s and luckily for us, they were prolific writers.

    The papers do not give much attention to the "do species mix" question but do talk about why they occur in the same areas and the adaptations of the digestive tracts that made their coexistence possible. The second paper shows a table where different species were shot from the same location.

    Merry Christmas late,

    FOODS OF ROCK AND WILLOW PTARMIGAN IN CENTRAL ALASKA WITH COMMENTS ON INTERSPECIFIC COMPETITION http://elibrary.unm.edu/sora/Auk/v08...0271-p0281.pdf

    WINTER DIETS, GUT LENGTHS, AND INTERSPECIFIC COMPETITION IN ALASKAN PTARMIGAN
    http://elibrary.unm.edu/sora/Auk/v09...0737-p0746.pdf
    Go Big Red!

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    I recall having seen these papers some time ago and they left me thinking kindly of the poor soul whose task it was to measure ptarmigan guts! Only very few times have I ever seen a ptarmigan up in a aspen budding, and never in a cottonwood. Interesting stuff, but so much more to know. Thanks for posting it. Have a great new year!

    Jim

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    Great resources- thanks for posting 'em.

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    PG, Thanks for posting these. You might also look at some of the ptarmigan nutrition work done by West and Meng in the 60s at UAF (try Google Scholar). While they primarily focus on diet, it is not a big stretch to guess that habitat partitioning is driven by diet. Robert Moss also had a very interesting paper, 'The digestion and intake of winter foods by wild ptarmigan in Alaska,' in which he describes the energy budgets of all three ptarmigan species. Willows appear to have much higher energetic costs than the other two species, possibly due to their feeding ecology - they feed on woodier twigs moreso than the other species, and tend to be in more exposed habitats while feeding. I guess it might have some effect on how the three species overlap.
    After thinking a bit more about mixed flocks of ptarmigan, I think that only during migration (September/October and March/April) have I seen rocks and willows together. This makes sense, as they are highly vulnerable to predation at this time, and more birds together decreases the chance of any one bird getting nailed by a predator. Where I have seen birds in close proximity during the winter months, there were small groups close together of separate species, but I would not go so far as to call them truly mixed flocks.

    Jim, as to your comment on seeing birds budding on aspen - I have only observed this in willows, and sometimes in really odd places (downtown Fairbanks, for example). Aspen is very nutritious, but is difficult to digest (I'm stretching here from some studies in moose), so maybe it is a trade-off between nutrition and digestibility.

    If it ever gets back into the reasonable zone (above zero), I'll have to get the dog out and do some more 'sampling' to support my theories... I'll be sure to report my findings to the group...

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    Miller,

    I'll spend some time researching those papers next fall probably as I didn't even fully read the ones I posted. There is some neat older stuff out there for certain. This was just a preview and there were many tangents I could have taken to get to more.

    I'm looking forward to some observation of birds and then some Audubon-type sampling like you referred to. They certainly occupy the same areas but to call it mixing may be a stretch. I'm sure it's happened out there in the wild but it doesn't sound like it's typical.

    Prairie Guy
    Go Big Red!

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