more glaucous-thing ramblings

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Posted by Phil Pickering (208.46.229.168) on April 18, 2001 at 08:44:18:

I've never been to Alaska, and I'm not aware of actual studies done on hybridization either genetically or through observations on breeding grounds, so I would agree with Bill that it may not be possible to say with absolute certainty that a hybrid (or backcross) could look like this. However, thanks in part to what we do know about those wonderful (aaarg) Western x Glaucous-winged, I think it's reasonable to infer that a gull like this, that is one apparently showing a range of characteristics that, taken as a whole, seem to be intermediate between phenotypical examples of two species, and borderline or possibly even outside the range of either, has genetic influence of both.

To state it concisely, I think this bird appears most like a small (barrovianus) Glaucous, but shows apparently atypical traits that seem to all vary from phenotypical for that form in a way that trends directly into Glaucous-winged. These seem to be the density and apparent irregularity of the remnant covert markings, head shape, chunkiness of the body, body/head proportions, leg length (I think the legs are a bit proportionately long for a small Glaucous), and most obviously the bill pattern.

I'd go farther. I've seen enough examples (a dozen or more in person and even more in photos) of birds that show a highly variable, but always intermediate range of characteristics between Glaucous and GW that, although I personally can't say I KNOW anything for sure, I do think it's very likely that first generation hybrids are fertile. The situation seems smeared out in way that mirrors what we know about Western x Glaucous-winged (and what we are learning about thayeri x glaucoides) to the point that it seems likely that there is a relatively free gene flow between these two species. In this light, IMHO the best "title" for this bird is a (presumed) small-end Glaucous showing introgression with GW. I also think it's likely (again aaarg) that a good percentage of west coast birds that appear to be pure Glaucous at a glance (like this guy) show introgression that might only be discernable (if it is at all) by studying the bird at close range.

It's also possible that the average (non-gull-obsessed) birder wouldn't find this important or interesting, and a Glaucous that was 93.75% or whatever pure would be close enough not to worry about. In that sense perhaps this IS a "Glaucous".

I'd also agree with Bill that birds like this tend to be seen more often in spring, presumable due to fading both in plumage and in bill pattern. It may be that in fall or early winter this bird would have had more black or duskiness in the bill, and would have been less likely to be ID'd as a pure Glaucous.

Cheers,

Phil Pickering
Lincoln City, Oregon

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Re: more glaucous-thing ramblings Mitch Heindel 22:09:48 04/20/01 (0)

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: I've never been to Alaska, and I'm not aware of actual studies done on hybridization either genetically or through observations on breeding grounds, so I would agree with Bill that it may not be possible to say with absolute certainty that a hybrid (or backcross) could look like this. However, thanks in part to what we do know about those wonderful (aaarg) Western x Glaucous-winged, I think it's reasonable to infer that a gull like this, that is one apparently showing a range of characteristics that, taken as a whole, seem to be intermediate between phenotypical examples of two species, and borderline or possibly even outside the range of either, has genetic influence of both. : To state it concisely, I think this bird appears most like a small (barrovianus) Glaucous, but shows apparently atypical traits that seem to all vary from phenotypical for that form in a way that trends directly into Glaucous-winged. These seem to be the density and apparent irregularity of the remnant covert markings, head shape, chunkiness of the body, body/head proportions, leg length (I think the legs are a bit proportionately long for a small Glaucous), and most obviously the bill pattern. : I'd go farther. I've seen enough examples (a dozen or more in person and even more in photos) of birds that show a highly variable, but always intermediate range of characteristics between Glaucous and GW that, although I personally can't say I KNOW anything for sure, I do think it's very likely that first generation hybrids are fertile. The situation seems smeared out in way that mirrors what we know about Western x Glaucous-winged (and what we are learning about thayeri x glaucoides) to the point that it seems likely that there is a relatively free gene flow between these two species. In this light, IMHO the best "title" for this bird is a (presumed) small-end Glaucous showing introgression with GW. I also think it's likely (again aaarg) that a good percentage of west coast birds that appear to be pure Glaucous at a glance (like this guy) show introgression that might only be discernable (if it is at all) by studying the bird at close range. : It's also possible that the average (non-gull-obsessed) birder wouldn't find this important or interesting, and a Glaucous that was 93.75% or whatever pure would be close enough not to worry about. In that sense perhaps this IS a "Glaucous". : I'd also agree with Bill that birds like this tend to be seen more often in spring, presumable due to fading both in plumage and in bill pattern. It may be that in fall or early winter this bird would have had more black or duskiness in the bill, and would have been less likely to be ID'd as a pure Glaucous. : Cheers, : Phil Pickering : Lincoln City, Oregon

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