"Many years ago at Crow Valley Campground near Briggsdale in Weld County, I first wondered why so many migrating passerines, mostly Orange-crowned Warblers in late April, were frequenting the flowers of plains cottonwoods (Populus deltoides, Fig. 1). My initial assumption was that they were primarily feeding either on the flowers themselves, as Cedar Waxwings and House Finches sometimes feed on the petals of crabapples, or on the bees, wasps, and flies that pollinate the flowers. Some years later, after noticing that the cottonwood catkins along the Poudre River in Fort Collins were attracting many birds, I collected several dangling flowers. To my surprise the catkins contained the same insect, over and over. It was a whitish beetle larva, very similar to the pine bark beetle larvae found under the bark of dying pines, but smaller. I placed a few infested catkins in a jar in my "lab" (a.k.a. my kitchen) and waited. What emerged weeks later were gray, long-snouted weevils in the genus Dorytomus (Fig. 2). Since then, my investigations of the known "birdy" cottonwood sites in Colorado, including the Lamar Community College Woods and Bonny Reservoir, have consistently produced the same result: Dorytomus larvae in the cottonwood catkins. I propose that the catkin-infesting larvae of Dorytomus weevils are an underappreciated source of food for many bird species in spring migration, wherever cottonwoods grow in Colorado...."
http://cobirds.org/JournalArchives/2010-2019/2011%20Vol%2045/CB_2011_45_2_Apr.pdf
Some pics of Dorytomus weevils: http://tiny.cc/g0roky
On Thursday, April 20, 2017 at 5:00:52 PM UTC-6, Tom Wilberding wrote:
Hello all,
Enjoyed a morning of early spring birding with Michael Kiessig at Chatfield today. Thomas Holub found a McCown's longspur at the Model Airplane Field yesterday; seems the the bird is still there. Saw American pipit at the swim beach, various yellow-rumped warblers, the eastern phoebe near the Kingfisher Bridge concrete outhouse, Swainson's hawks, turkey vultures, house wrens, vesper sparrows, Say's phoebes, and Franklin's gulls.
Michael yesterday noticed a very productive (magic) plains cottonwood near the swim beach. It attracts starlings, flickers, robins, and many yellow-rumped warblers. I believe it is a male tree with catkins just turning red. Lots of birds there again today. Do insects like those red catkins? Dave Leatherman, can you explain the magic?
Finally, Michael noticed a renegade-looking red-tailed hawk, photo below. Anybody know what it is?14 photo slideshow with audio here: https://goo.gl/77dVp5
Cheers!
Tom Wilberding
Littleton, Colorado
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