Thayer's Gull (thayeri)

(last update: January 22, 2013)

Thayer's Gull x Herring Gull hybrid adult, February 08 2009, Swan Lake Nature Sanctuary, Victoria, Vancouver Island, BC. Picture: Guy Monty.

Visit: Guy's Flickr site.

Birds in winter (non breeding) plumage. This bird shows all the physical properties of a Herring Gull. It's primaries are patterned like a Thayer's Gull. Presumably a Herring Gull x Thayer's Gull hybrid. Comment of Guy: This bird was way outside of what is typical for a Thayer's Gull. The eye color wasn't really a consideration and can vary in Thayer's. Probably 15-20% of the thousands of Thayer's Gulls we see here on Vancouver Island each year have light eyes. Few of them are this light, and so free of specks, but it's obvious that eye color isn't a definitive field mark for Thayer's or Herring for that matter.
This bird was much larger than any Thayer's Gull I have ever seen. It approached the size of the Glaucous-winged x Western Gull hybrids that it was associating with. The bill was much longer, and thicker, than in any Thayer's Gull I have ever seen. The head size and shape is off for Thayer's Gull, and bang on for Herring Gull.
The mantle color appears darker in this photo than it did in the field, and is an artifact of the sun being behind the bird. The true color is closer to what you see behind the nape, and is much closer to what is typical for a Herring Gull.
Believe me, we agonized over this gull for a long time. I originally thought it was a Herring Gull, until having better looks at the primary patterning. I honestly think this is a hybrid between those two species. I have no problem with calling it a "probable" though. Nothing is certain with gulls! ;-)

Guy sees quite a few Herring Gull x Glaucous-winged Gulls on Vancouver Island, and this bird lacks some of of the best field marks for that hybrid combination. The bill isn't nearly as large or heavy in the tip as in a Herring Gull x Glaucous-winged Gull. The primaries are still jet black, unlike the gray primaries expected in Glaucous-winged hybrids. Most hybrids of that type have a fairly dull eye.

Apparently Herring and Thayer's Gulls do occupy the same breeding areas along the west shore of Hudson's Bay, and there are some mixed colonies there. However, it was the lack of interbreeding in these colonies which led to the two types being split into seperate species. Being gulls though, I can't imagine that it never happens. I agree that it's possible that Herring x Thayer's offspring might not be distinct enough that such birds rarely raise anyones interest.
The birds structure and the primary patterning make me lean away from Glaucous-winged and Glaucous. The wing markings certainly seem to point to Thayer's Gull.