Date: 10/27/18 10:45 am
From: David Steingraeber <David.Steingraeber...>
Subject: Re: [cobirds] subspecific ID of the Boulder Co. Fork-tailed Flycatcher
In addition to subspecies identification, the pronounced
emargination/notching of the 3 outer primaries that Christian pointed
out also provides confirmation that the bird is a male. According to
both Pyle's /Identification Guide to North American Birds, Part 1 /and
Howell's /Rare Birds of North America,/ females of ssp. /savana/ have
tapered/pointed outer primaries that are not strongly notched.  Here's a
figure from Howell's book showing the distinction:


On a related note, a relevant research paper on Fork-tailed Flycatcher
wing morphology was recently published in the journal /Evolutionary
Ecology/: Provinciato, I.C.C., M.S. Auaujo & A.E. Jahn. 2018. Drivers of
wing shape in a widespread Neotropical bird: a duel role of sex-specific
and migration-related functions. /Evolutionary Ecology /32: 379-393.
In the paper, the authors suggest that wing shape differences between
males and females, and between the migratory ssp. /savana /and the
non-migratory ssp./monachus, /are the product of a mix of selection
pressures, with some (e.g., efficiency in foraging, predator avoidance,
and migration) acting on both males and females, while others are
sex-specific (e.g., male courtship displays).

David Steingraeber
Fort Collins


On 10/26/2018 7:58 PM, Christian Nunes wrote:
> Hi all,
>
> When Fork-tailed Flycatchers show up in the US or Canada, birders
> often attempt to ascribe them to one of the two likely populations
> from which they might come: the widespread South American austral
> migrant, /savana/, or the resident /monachus/ of Central America.
>
> This article summarizes the occurrence of each Fork-tailed Flycatcher
> subspecies north of their normal range and offers guidance on how to
> separate them:
>
> https://www.westernfieldornithologists.org/archive/V25/25(3)%20p0113-p0127.pdf
> <https://www.westernfieldornithologists.org/archive/V25/25%283%29%20p0113-p0127.pdf>
>
> The most reliable feature is the level of primary emargination. The
> nominate /savana/ has pronounced emargination on the outer three
> primaries, while /monachus/ shows this notch on only the outer two
> primaries. The more likely /savana/ also tends to lack a white collar
> around the back of the neck, where the gray back color often meets the
> black nape.
>
> Here are some photos of the Boulder County bird that elucidate these
> differences:
>
> https://ebird.org/view/checklist/S49438796
> <https://ebird.org/view/checklist/S49401824>
> https://ebird.org/view/checklist/S49381812
> https://ebird.org/view/checklist/S49381592
> https://ebird.org/view/checklist/S49411141
>
> Based on these shots, the Boulder bird can be identified as being from
> the nominate South American population, /savana/. Folks might want to
> update their notes if they're interested in that level of ID.
>
> Christian Nunes
>
> Lyons, CO
>
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