Date: 3/31/17 6:50 am
From: <5hats...>
Subject: [obol] an observation on gulls
Although I have not read the stuff about the debate between Smith and Snell, nor am up to snuff on any DNA studies on northern gulls, I find this discussion on the proposed lumping of Iceland and Thayer's Gulls very interesting. After reading some of the information presented on OBOL about the studies of the two on Baffin Island, I don't see how it is much different from what is currently going on between Western and Glaucous-winged Gulls at the zone of overlap between their breeding ranges. Any birder that has spent five minutes of time looking at gulls on the Oregon Coast during winter knows that among the Westerns and Glaucous-winged species there are many hybrids. I have estimated that the percentage of hybrids is often around 60% of the total group of several hundred often gathered at the Yaquina Bay south jetty. Given the current discussion of lumping the northern gulls, it makes one wonder if we are not eventually on the same path with the western ones.
One thing that hasn't seemingly been mentioned much in the discussion is that worldwide gull populations are increasing. Increased populations=expanding ranges; expanding ranges=a stronger likelihood of distinct breeding populations coming in contact with one another, which= an increased likelihood of hybridization. It is the opposite principle of what normally results in speciation: namely distinct populations diverging as a result of geographical isolation or some other limiting factor, as is the case with Plain Titmouse being split into Oak and Juniper Titmouse.
Both cases are strong evidence for the fact that things reproduce after their own kind, and that within the framework of kind there is great flexibility regarding speciation. It seems to me entirely possible that at one point during the Ice Age there may have been a fairly long term and sharply divided separation between gull populations which allowed those populations to develop distinctive characteristics, and now with warmer temperatures and expanding ranges the opposite situation is occurring. It may give both birders and taxonomists headaches, but it is what we should expect within the framework of biological reality.

Darrel


 
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