Tom Litteral posted this morning about flocks of Bohemian Waxwings feasting on
insects hatching from the Yampa River in Steamboat Springs, visible from
multiple vantages. I forwarded his COBIRDS message to my entomologist buddy
Dr. Boris Kondratieff at CSU. Boris has described for the first time over 100
species of aquatic insects, so to call him an "expert" on the subject matter of
this situation is an understatement. His response to my question about which
insect is likely at the heart of the waxwing frenzy in Steamboat Springs was
roughly, "could be chironomid midges or the common stonefly, Capnia vernalis,
which hatches at this time of year."
I'm betting the stonefly is the answer. Capnia vernalis is also known as the
"Belly Snowfly", "Little Black Stone", "Black Hare's Ear", and the "Canadian
Willowfly". It is one of the so-called "winter stoneflies", with the emergence
period being usually Feb-April. It is common, occurs in large, warmer rivers
of the plateau portion of western CO. Maps available on-line of its U.S. range
show it occurring from northern NM north and west to Montana and ne
Oregon/western WA, respectively, and there is an outlying population in
northeastern MN. With "Canadian Willowfly" being one of its common names, this
implies a range that includes at least parts of western Canada (which would be
within the heart of the Bohemian Waxwing's breeding, migrating, and wintering
ranges).
Would be cool to document with specimens the basics of the situation Tom
brought to our attention. If you, Tom, or anyone else going that way could
catch a few (15-20), put them in a vial filled to the brim (no air bubbles)
with rubbing alcohol, and get them to me, I could in turn get them to Boris.
His confirmation would be a nice little piece of information about a
charismatic Colorado visitor and situation. IF the insect involved is, indeed,
the Belly Snowfly, maybe its common status, combined with the predictability of
late winter-early spring hatches, is part of why Bohemian Waxwings might be
more regular in the northwest corner of CO than elsewhere, where major food
resources (mostly tree berries) aren't quite as predictable.
Lots of conjecture and hypothesizing here, but that's how answers to questions
begin to take shape, right?
Thanks to Tom Litteral for his post.
Dave Leatherman
Fort Collins
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