Path: utzoo!attcan!uunet!ginosko!gem.mps.ohio-state.edu!tut.cis.ohio-state.edu!brutus.cs.uiuc.edu!apple!rutgers!sunybcs!joey.cs.buffalo.edu!dmark From: dmark@joey.cs.buffalo.edu (David Mark) Newsgroups: rec.birds Subject: Re: What is this bird?? Message-ID: <10776@eerie.acsu.Buffalo.EDU> Date: 23 Sep 89 14:56:05 GMT References: <3791@helios.ee.lbl.gov> <48214@oliveb.olivetti.com> <48269@oliveb.olivetti.com> <3215@nmtsun.nmt.edu> Sender: nobody@acsu.buffalo.edu Reply-To: dmark@joey.cs.buffalo.edu.UUCP (David Mark) Distribution: na Organization: SUNY @ Buffalo Lines: 45 In article <3215@nmtsun.nmt.edu> john@nmtsun.nmt.edu (John Shipman) writes: > >This business of Glaucous-winged x Western gulls really >bothers me. I have a database of all the Christmas Bird >Counts from 61-62 through 87-88, and when I look at the >occurrence of this form, it looks like it's spreading >rapidly on the west coast. In the 69th CBC there are no >records of this hybrid. In the 79th, there are records in >two counts in Washington (Grays Harbor and Olympia), one in >Oregon (Eugene), and none in California. The 87th, however, >has records all over northern California (including the Bay >Area and Monterey area) and even two in Los Angeles. > >But I'm afraid it's not the BIRD that spreading, just >information on how to identify it! This is one of the >big problems in interpreting field data, and in my line >of work it bites me all the time. John, this diffusion of information about a 'new' form, rather than diffusion of the form itself, was exactly the point in my 1981 article: "Thayer's Gulls from western Christmas bird counts: a cautionary note." which appeared in American Birds, 35, 898-900. Thayer's Gull was split from Herring in 1973. The percentage of Thayer's Gull among Thayer's + Herring in the west coast states and province was total B.C. 1973 5.2% 27.2% 1974 9.5% 21.9% 1975 15.3% 57.5% 1976 20.8% 70.3% 1977 20.3% 82.0% 1978 11.9% 34.6% If the 1976-77 data represent some sort of equilibrium, then it took 3-4 years for knowledge of a "new species" to spread through the birding community. And I bet there are positive feedbacks, with ambiguous cases going by default into the more common form, rather than being left as "gull sp.". Obviously, most amateur birders (including myself), are species-centric, and news of a hybrid form would spread much more slowly and irregularly, I imagine. David Mark dmark@cs.buffalo.edu