Yellow-rumps: early birds

Yellow-rumped Warblers are the first of that family to return to Minnesota in the spring. They've been reported throughout the Twin Cities for about two weeks. Why are they able to survive uncertain spring weather when other warbler species must wait? What, for example, do Yellow-rumps eat, warblers being birds that rely on insects for nourishment? Local birder Rick Hoyme, writing on the listserv operated by the Minnesota Ornithologists' Union, answered those questions. His information was expanded in turn by Dan Tallman, a Northfield birder with a long academic ornithological background.

The secret of the Yellow-rump is long intestines. Right, intestines, the longest digestive tract of any of our warblers. This allows the bird to digest seeds, and to extract maximum nutrition from them. These birds have other digestive distinctions that allow them to maximize energy benefits from a variety of foods other warblers would not and could not touch. This species can be less choosey about what it eats. Yellow-rumps need not rely on insects. One particular digestive advantage is the species' ability to digest waxes. This allows it to eat bay berries, wax myrtle, and a variety of other berries and plant parts.

So, we get some welcome bright flashes of black and white and gray and yellow weeks ahead of the May migration that will rush through here in two or three weeks. The benefit to the Yellow-rumps? It's seems to be more matter of geography than defined benefit. Many of these warblers winter in the U.S. They arrive earlier than their warbler cousins because of a shorter journey. They will be on territory two weeks or so before other warbler species, but will nest not more than a week earlier. That's because nesting – creation of eggs and feeding of hatchlings, requires food of higher energy content: insects. Once the insect population is up and running, nesting can proceed.

Some of this information comes from monograph number 376 in the Birds of North America series. As is the case with many bird species not difficult to find, many questions about the bird's biology and behavior are followed by: No information. Study just hasn't been done, for whatever reason, perhaps simply lack of a graduate student willing to choose this species for two-years of research and the resultant thesis. The birding world is filled with unanswered questions about common (and uncommon) species.

Dr. Tallman's birding web site and blog are rewarding places to visit. He is a very active birder, as well as a bird bander, and always has something interesting to say (photos, too). The addresses are

http://dantallmansbirdblog.blogspot.com/

http://dantallmansbirdblog.blogspot.com/p/home-page.html

This Yellow-rumped Warbler was photographed in May 2010 in Orono.