Thayer's Gull (thayeri)

(last update: January 22, 2013)

Thayer's Gull 2cy January (1st cycle)

First winter Thayer's Gull, especially males, can be difficult to identify in California where various hybrid combinations and also Herring Gulls occur. One such hybrid combination is Glaucous-winged x American Herring Gull. Poiunts to look for in Thayer's are:

- relatively small size
- thin, parallel-sided bill
- slimmer, more elongated body than other large gulls, with fairly long primary projection
- strong dark peppering on inner primaries (usually absent in GWGU and AHGU, but often seen in 'good' Thayer's Gulls).
- distinct but irregular barring on greater coverts (usually plainer pattern in GWGU and AHGU, especially in the former species)
- full juvenile plumage (in late January)
- frosty, almost whitish appearance of scapulars.

A good set of Thayer's pictures can be view in the album of Brandon Holden.

Thayer’s Gull has several record in Europe, and is one of the prime serched after Nearctic gull species. Identification truely is a matter of subbtle features and characteristics, as this taxon may look like Iceland Gulls on the one hand, but may recall small female Herring Gulls on the other. Still it is none of both. The likely (narrow?) intergradation zone of hybridisation, which is a general accepted concept in Canada and the US make things more complicated: "How to satisfactory exclude such hybride kumlieni-thayeri birds from pure individuals?"
The challenge was taken on by Danish birder Kent Olsen, who photographed gulls in Hvide Sande Harbour, Denmark on February 04 2012. After putting a link to images on the ORG forum, questions were raised whether this could be a 1st winter Thayer's Gull? The next months Kent has studied many images on the web in great detail and some of his findings are copied on this page. For more details, please visit Kent's weblog!

Introduction by Kent Olsen

By presenting photos of different accepted Thayer’s Gulls and other species, I hope that I have been able to document that all characters questioned are within the variation of Thayer’s Gull.  I acknowledge that single individuals could be misidentified and have thus tried to select several different individuals for each character in order to come around such issue. I hope you will find that the most parsimonious explanation for the Danish gull is that it is a Thayer’s Gull, as are most of the other ones which have occurred in recent years in western Europe, even though they vary somewhat in appearance just like the juveniles of all large white-headed gulls.

The following list of pro-thayeri plumage characters support the ID:

• relatively long primary projection
• primaries are dark, the darkest part of the plumage, though only a little darker than tertials
• primary tips are highlighted by narrow pale fringes, forming thin chevrons
• distinct dark peppering on inner primaries5.subterminal marks on inner primaries are pale and almost translucent
• silvery-grey underside of the primaries with dark trailing edge on outer primaries
• tertials exhibit complex pale patterning concentrated toward the feather tip
• greyish cast to tertial centres
• characteristic pattern to the juvenile scapulars with small brown centres and paler browninternal colour
• extensive barring to the undertail coverts and uppertail coverts
• venetian blind created by the contrast between the inner and outer webs of the primaries, i.e. obvious silvery-grey inner webs to outermost primaries
• distinct dark secondary bar
• secondaries have a thin, dark subterminal ‘arrowhead’ mark
• secondaries, especially outer most, are paler greyish brown
• bright pink leg colour
• relatively thin bill
• pale eye-ring

Evaluation of JIZZ and plumage: When evaluating jizz and plumage one should always remember that single situation photos will not always do a bird justice. It is always best to make a judgement based on multiple photos capturing different posture/behaviour/ situations. Keep that in mind when evaluating this record.

Kirk Zufelt has written two blog posts on size variation in Thayer's Gull part 1 and part 2 based on experiences from eastern Lake Superior in Ontario. He says that: ‘Thayer's Gull is thought of by many as a relatively finely structured gull with a rounder head and finer bill than the Herring. Indeed the females are usually structured in this fashion. This however is not a diagnostic field mark at all. The male Thayer's can be quite robust and to my eye are near indistinguishable from the Herring Gull by structure. In fact many male Thayer's are much more robust and "Herring Gull-like" in structure than the female Herrings. In the field I look closely at all the round headed petite look birds with most of them ending up being Herrings. The bottom line is the structure is a good way to narrow down the field but it is far from diagnostic’.

Next to a Great Black-backed Gull.

Head and Bill: note the small-to-moderate gonydeal expansion typical of the species.

Several have stated that head profile in the Danish gull is very Herring Gull-like and head size is relatively large. Even though this is certainly not uncommon in male Thayer’s Gull it has provoked doubt and fuelled hybrid speculations among birders who live in hybrid hotspots such as the US West Coast where hybrids plumage-wise almost make a complete match with the wintering Thayer’s and where people are left with size, proportions and jizz to make a safe ID.

I have trouble understanding that even though so many experienced gull watchers have joined this discussion the main argue against the Danish gull being a Thayer’s is size and proportions of especially head and bill. I expect we all have experience with gulls changing appearance in relation to behaviour and posture.

I’m not stating the Danish gull transformed into a small petit female, but the relative large headed appearance certainly changed. When watching the gull on the roof I actually had to view my camera display for finer details to make sure it was the same gull. I acknowledge that proportions and size strongly indicates that it is a male, but I believe that the scary appearance is also caused by an artefact created by posture and behaviour and possibly also the telephoto effect induced by my Canon 500 mm lens.

The head profile changed dramatically between a relaxed standing bird on the roof with a rather round head and gentle expression and when it feeds with its wings raised continuously, while balancing on the container edge and in constant combat with the nearby large gulls as in most photos.

The pale eye ring has also been discussed, but again that character is also seen in other Thayer’s Gulls such as these from Lake Michigan, Califonia, California, Minesota, Ontario, Ireland, British Colombia and Ontario.

People have criticised the head and bill shape. However, where comparing with these gulls Ontario, Ontario, Ontario, Ontario, Minesota, Nevada, Japan, Califonia, Califonia, Califonia, Califonia, Califonia, Lake Michigan, Newfoundland, British Colombia, Oregon, Japan, Japanand Norway. I see so many similarities with the Danish gull here, here and here. Please note hove the head shape changes with behaviour, i.e. the flat forehead seen when it was feeding among Great Black-backed Gulls vanished when it landed on the nearby roof.

For additional comparison look at figure 6 in this PDF on plumage development in captive Thayer’s chicks caught on Victoria Island in Arctic Canada. What a massive bill and flat forehead.

Most images show the bird with a long bill, flat head and snouty look. I can understand that, in a Californian context, "large and snouty" is disconcerting. However, if you check images from the breeding range, it is clear that large, snouty structure with strong billare perfectly normal in Thayer's Gull.

Colour tone and white balance in digital photos: Note that the Danish gull was mainly seen feeding in the shade on a very sunny day with a clearblue sky. In such a situation the natural light puts the automatic white balance in the digitalcamera on a test and often causes the cold colour tones to be exacerbated.In the two photos below, the difference in appearance is striking and the automatic whitebalance fails and add to the salt-and-pepper impression. In real life, the Danish gull lookedmore warm and soft in plumage colours then the auto shows and when the white balance is setto shade, the digital representation matches the live bird.

Chequered wing coverts and upperparts: People have argued that the irregular pattern on the greater coverts and the chequered upperparts are wrong for Thayer’s Gull even though identical patterns are also seen in several individuals in ‘Gulls of Europe, Asia and North America’ by Olsen & Larsson and ‘Gulls of the Americas‘ by Howell & Dunn. To illustrate that the pattern seen in the Danish gull is within what is fully accepted as being part of the Thayer’s Gull plumage variation, I have collected photos of  other individuals with similar pattern.

Click for 1500 px image.