Hi all: With the recent report of an eastern Blue-gray Gnatcatcher in the northeast recently by Mark Peterson and Brad Steger, I thought this a good time to expound on the subject.
Bailey & Niedrach (1965) list the occurrence of only one subspecies of Blue-gray Gnatcatcher in the state, the widespread western form obscura (listed in B&N as amoenissima, though Pyle [1997] subsumed that form into obscura). However, relatively recent interest by birders in subspecies identification has shown that not only are the two widespread forms (western, eastern caerulea) are diagnosable on plumage, vocalizations are also different. Sibley (2000) notes the relevant plumage differences (pg. 397 in big Sibley) and states the following about vocalizations: "Western song significantly different: lower, harsher, less varied .... Western birds average lower and harsher calls than Eastern; shorter and more strongly descending... more similar to House Wren and all other gnatcatchers." In many, if not most, species with Rockies forms and eastern/northern forms, the Rockies form tends to migrate earlier in fall than does the eastern/northern form, such that most have departed the state (if they're going to depart the state) relatively early in fall. Simply on date alone, I would have suspected that Mark and Brad's gnatcatcher was an eastern bird, but the location well out on the plains also suggests that. It does so, because the Rockies forms of such species also seem to be able to not deviate too much from a north-south route and many of such species are relatively rare that far east on the plains. I encourage Colorado's birders to pay closer attention to gnatcatchers on the eastern plains and any gnatcatcher after September, though the Blue-grays that winter in the Grand Junction area may very well be western birds. However, closer scrutiny of those is also in order, just to make sure! With some careful field work, Colorado's birders can continue to add to our knowledge of distribution of the state's birds. Entering your data on Blue-gray Gnatcatchers to subspecies group into eBird provides a great repository for such information, one that makes your data available to a host of birders and ornithologists interested in bird distribution. However, as ever for subspecies, I also urge caution in identifying individuals to subspecies, as for many species -- and Blue-gray Gnatcatcher is certainly one of such, subspecific ID requires good and lengthy looks. Sincerely, Tony Leukering Villas, NJ Literature Cited Bailey, A. M. and R. J. Niedrach. 1965, Birds of Colorado. Denver Museum of Natural History. Pyle, P. 1997. Identification Guide to North American Birds, part I. Slate Creek Press, Bolinas, CA. Sibley, D. A. 2000. The Sibley Guide to Birds. Alfred A. Knopf, New York. -- You received this message because you are subscribed to the Google Groups "Colorado Birds" group. To post to this group, send email to cobirds@googlegroups.com. To unsubscribe from this group, send email to cobirds+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/cobirds?hl=en.
