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 -- You received this message because you are subscribed to the Google Groups "Colorado Birds" group. To unsubscribe from this group and stop receiving emails from it, send an email to cobirds+unsubscr...@googlegroups.com. To post to this group, send email to cobirds@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/cobirds/SNT148-W387D6941CCC6FDFBD2A50FC1770%40phx.gbl. For more options, visit https://groups.google.com/d/optout.