Lessons from Travels: Glaucous Gull Hybrids

by Carl Strang

I conclude the Lessons from Travels series with a question that remains open to this day. Why does a portion of the glaucous gull population at the tip of the Yukon-Kuskokwim Delta show signs of hybridization with another species?

Glaucous gulls in a nesting colony

Glaucous gulls in a nesting colony

My study required me to shoot a limited number of gulls for various measurements both external and internal, and I found that the wingtips of some of them showed faint gray patterns reminiscent of other species. The eyes also occasionally showed darker color variations different from the pale glaucous gull ideal. This is what took me to Adak Island.

The nearest candidates for hybridization were glaucous-winged gulls, which are common in the Aleutians.

The nearest candidates for hybridization were glaucous-winged gulls, which are common in the Aleutians.

I documented the descriptive data (DNA comparisons were well in the future), but could not reach a clear conclusion. Two decades later I was contacted by Tim Bowman, a wildlife biologist with the U.S. Fish and Wildlife Service in Alaska, who was doing impressive work with glaucous gulls in the same region. He had found that the gull population had ballooned, thanks to improved gull winter survival off the Alaska fishing industry. He also looked at the hybridization question I had raised. By then, molecular studies were feasible but very expensive, and he had not found the funds to proceed. He did note, however, that there did not appear to be a graded change in those physical measures connecting the glaucous and glaucous-winged gull populations. Perhaps someday someone will clarify this, but all in all it has to be regarded as more a curiosity than an important question.

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