Post by Gord on Feb 7, 2017 23:52:24 GMT -8
Thanks, Randy, for suggesting this great topic. Sorry it took so long! One would think one of my favourite subjects wouldn't take a month to get to 
Let's dig in
Thayer's Gull and Herring Gull can be tricky birds to ID. 'Typical' specimens are pretty straight forward but there's always variation lurking among the flocks of gulls we look at. I'll just talk adults in this thread. I've found that learning the adults well does help a lot to lead up until one's ready to take the plunge in identifying them in the various plumages they have over the four years it takes to go from the brown juvenile-feathered birds to the adult plumaged white birds. Walk before we run.
Here's a typical Herring Gull how we'd like all of them to look like.
And a typical Thayer's Gull that would be awesome if all looked like this
Wing structure is something that's helpful in these birds. Here's a Thayer's Gull wing with the primaries numbered as found in the literature. One would relate to the primary feathers as P10, P6 and so forth. In describing below one would say the primaries have dark markings down to P5.
Bill structure, while not always a solid fieldmark, is worth mention. The 'gonydeal angle' is found on the lower mandible between the highest point and the bill tip. See photo below to see an illustration of this and the variations between species.
Slaty-backed Gull showing a fairly pronounced angle (Typical Herring Gull similar). Pardon how I shamelessly found an excuse to use this photo.
Thayer's Gull with a gentle angle as is usually expected. Note the greenish cast to the bill; a good supporting fieldmark to consider when working out an ID. Also Herring often has a bit of black markings on the bill at the red dot during the winter while Thayer's often lacks this.
Western Gull with a good angle as well as the bulbous looking tip to the overall bill appearance
Herring Gull is a larger, more robust-looking gull over Thayer's Gull. A perched bird's wingtips on both species looks black with Thayer's sometimes a tad dark grey being an acceptable colour for a Thayer's. When the wings are spread the amount of black/dark grey is a key feature to look at. Sometimes a difficult bird to ID can't be confirmed until the wings are seen stretched out. Herring Gull adults have pale eyes while typical Thayer's Gull has dark ones. But not always as we'll see later.
I usually pick Herring Gulls out of the flock by spotting the black wing tips. Some Herring Gull specimens from over the years I dug out of my photo library.
In flight the black in the primaries is fairly extensive and solid when seen from top and bottom and dark markings always goes down to at least P5
This guy is growing in P9 and P10 after molt thus the slightly odd look. Dark markings down to P4
I found this to be an interesting guy with the dark neck streaks. There is a bit of dark marking down to P4 on this individual too.
Thayer's Gull. These are a smaller gull and in a mixed flock of gulls are often noticeable to be a bit smaller. But some words of caution on size. Herring Gull found on the west coast tend to be a tad smaller than the ones out east. It is also a fact that males and females are differently sized with males larger both in body and often in bill size and even gonydeal angle. While size is a good clue, do use with a measure of caution. Thayer's are known to have dark eyes which lend to a gentle look. Bills are shorter than Herring (keep size between male and female AND simple variation between individuals in mind) and in the winter often have a greenish cast to it. Leg colour is often a stronger pink than Herring so long as the legs are not covered with mud. Head streaking is quite variable; I don't tend to give it much weight as there's better fieldmarks to look at.
Some photos of Thayer's Gull
This guy is in breeding colours in the spring thus no streaks on the head and neck. The only photo I have of a bird at this time of year.
Some flight shots. Note that when the wing is spread what looked pretty black on a folded wing is often more a dark grey. From below, the amount of dark colouring is restricted to the tips. From above the extent of dark colouring not as extensive as on Herring. I've seen birds with no dark on P5 with the dark marks going just to P6.
As was seen on a Herring Gull previously, this guy is just growing in P10.
No dark marks on P5 on this one. Note the strong pink legs!
Next some odd-balls to make things interesting. A small percentage of Thayer's Gull have been noted to have pale eyes rather than dark ones.
When I first saw this guy swim by I thought maybe a tad small for a Herring but look at the pale eye; must be a smaller female.
Then I saw the wings. Oops! Doesn't even go to P5! and P10 has very little back but large white 'mirrors' (gull lingo for the white parts in the primaries)
And another guy from Harrison River that I saw a the same place for two-three winters in a row. Note the greenish bill
Herring Gulls (and pale-eyed Thayer's) look fierce due to the eye colour and can cause one to call these uncommon pale-eyed Thayer's a Herring. Notice how the photoshopped pale-eyed Thayer's looks a lot more friendly
Photoshopped
The fleshy bit around the eyes is called the orbital ring. Herring Gull has a yellowish one while Thayer's has purple-pink.
Pale-eyed Thayer's
Yellow orbital ring Herring
Thayer's again
To finish off this massive post, a Thayer's usually will stick out in a crowd like this sleepy guy does with the smaller size and little bill.
BUT (no conversation about gull ID is complete without lots of use of the word BUT, USUALLY, OFTEN and SOMETIMES) as previously mentioned size isn't everything. Earlier on I showed this picture of a Thayer's. Notice the Glaucous-winged Gull on the left (one of our largest gull species)
A perfect example of how a small female bird can really throw one off when it comes to looking at size if you see the full shot below. And the Thayer's Gull that was next to it was not a large specimen in itself. But (but) closer examination shows a pretty strong gonydeal angle, a strong yellow bill and, of course, grey wingtips that pretty much are the same colour as the back. I should mention at this point hybridization. This is very common in gulls. Here, Western Gull and Glaucous-winged Gull are our most common hybrid. A small hybrid combining the features of the parent species could look like a Thayer's Gull at first glance. But small details on these birds are noticable often with a slightly darker grey back than should be seen on a Thayer's, a strongly angled bill possibly a bit thick at the tip to show the Western Gull influence. If stuck on an ID, it's perfectly acceptable to wave your hand and say 'hybrid' and move on. There's a good chance you're right and there's no point frustrating yourself on it when there's plenty of more typical examples to practice on. And when you get bored with the adults, there's always the juveniles!
I hope this was useful and not too rambling. This is a topic I enjoy so don't hesitate to ask questions or share photos for feedback. Happy gulling!
Let's dig in
Thayer's Gull and Herring Gull can be tricky birds to ID. 'Typical' specimens are pretty straight forward but there's always variation lurking among the flocks of gulls we look at. I'll just talk adults in this thread. I've found that learning the adults well does help a lot to lead up until one's ready to take the plunge in identifying them in the various plumages they have over the four years it takes to go from the brown juvenile-feathered birds to the adult plumaged white birds. Walk before we run.
Here's a typical Herring Gull how we'd like all of them to look like.
And a typical Thayer's Gull that would be awesome if all looked like this
Wing structure is something that's helpful in these birds. Here's a Thayer's Gull wing with the primaries numbered as found in the literature. One would relate to the primary feathers as P10, P6 and so forth. In describing below one would say the primaries have dark markings down to P5.
Bill structure, while not always a solid fieldmark, is worth mention. The 'gonydeal angle' is found on the lower mandible between the highest point and the bill tip. See photo below to see an illustration of this and the variations between species.
Slaty-backed Gull showing a fairly pronounced angle (Typical Herring Gull similar). Pardon how I shamelessly found an excuse to use this photo.
Thayer's Gull with a gentle angle as is usually expected. Note the greenish cast to the bill; a good supporting fieldmark to consider when working out an ID. Also Herring often has a bit of black markings on the bill at the red dot during the winter while Thayer's often lacks this.
Western Gull with a good angle as well as the bulbous looking tip to the overall bill appearance
Herring Gull is a larger, more robust-looking gull over Thayer's Gull. A perched bird's wingtips on both species looks black with Thayer's sometimes a tad dark grey being an acceptable colour for a Thayer's. When the wings are spread the amount of black/dark grey is a key feature to look at. Sometimes a difficult bird to ID can't be confirmed until the wings are seen stretched out. Herring Gull adults have pale eyes while typical Thayer's Gull has dark ones. But not always as we'll see later.
I usually pick Herring Gulls out of the flock by spotting the black wing tips. Some Herring Gull specimens from over the years I dug out of my photo library.
In flight the black in the primaries is fairly extensive and solid when seen from top and bottom and dark markings always goes down to at least P5
This guy is growing in P9 and P10 after molt thus the slightly odd look. Dark markings down to P4
I found this to be an interesting guy with the dark neck streaks. There is a bit of dark marking down to P4 on this individual too.
Thayer's Gull. These are a smaller gull and in a mixed flock of gulls are often noticeable to be a bit smaller. But some words of caution on size. Herring Gull found on the west coast tend to be a tad smaller than the ones out east. It is also a fact that males and females are differently sized with males larger both in body and often in bill size and even gonydeal angle. While size is a good clue, do use with a measure of caution. Thayer's are known to have dark eyes which lend to a gentle look. Bills are shorter than Herring (keep size between male and female AND simple variation between individuals in mind) and in the winter often have a greenish cast to it. Leg colour is often a stronger pink than Herring so long as the legs are not covered with mud. Head streaking is quite variable; I don't tend to give it much weight as there's better fieldmarks to look at.
Some photos of Thayer's Gull
This guy is in breeding colours in the spring thus no streaks on the head and neck. The only photo I have of a bird at this time of year.
Some flight shots. Note that when the wing is spread what looked pretty black on a folded wing is often more a dark grey. From below, the amount of dark colouring is restricted to the tips. From above the extent of dark colouring not as extensive as on Herring. I've seen birds with no dark on P5 with the dark marks going just to P6.
As was seen on a Herring Gull previously, this guy is just growing in P10.
No dark marks on P5 on this one. Note the strong pink legs!
Next some odd-balls to make things interesting. A small percentage of Thayer's Gull have been noted to have pale eyes rather than dark ones.
When I first saw this guy swim by I thought maybe a tad small for a Herring but look at the pale eye; must be a smaller female.
Then I saw the wings. Oops! Doesn't even go to P5! and P10 has very little back but large white 'mirrors' (gull lingo for the white parts in the primaries)
And another guy from Harrison River that I saw a the same place for two-three winters in a row. Note the greenish bill
Herring Gulls (and pale-eyed Thayer's) look fierce due to the eye colour and can cause one to call these uncommon pale-eyed Thayer's a Herring. Notice how the photoshopped pale-eyed Thayer's looks a lot more friendly
Photoshopped
The fleshy bit around the eyes is called the orbital ring. Herring Gull has a yellowish one while Thayer's has purple-pink.
Pale-eyed Thayer's
Yellow orbital ring Herring
Thayer's again
To finish off this massive post, a Thayer's usually will stick out in a crowd like this sleepy guy does with the smaller size and little bill.
BUT (no conversation about gull ID is complete without lots of use of the word BUT, USUALLY, OFTEN and SOMETIMES) as previously mentioned size isn't everything. Earlier on I showed this picture of a Thayer's. Notice the Glaucous-winged Gull on the left (one of our largest gull species)
A perfect example of how a small female bird can really throw one off when it comes to looking at size if you see the full shot below. And the Thayer's Gull that was next to it was not a large specimen in itself. But (but) closer examination shows a pretty strong gonydeal angle, a strong yellow bill and, of course, grey wingtips that pretty much are the same colour as the back. I should mention at this point hybridization. This is very common in gulls. Here, Western Gull and Glaucous-winged Gull are our most common hybrid. A small hybrid combining the features of the parent species could look like a Thayer's Gull at first glance. But small details on these birds are noticable often with a slightly darker grey back than should be seen on a Thayer's, a strongly angled bill possibly a bit thick at the tip to show the Western Gull influence. If stuck on an ID, it's perfectly acceptable to wave your hand and say 'hybrid' and move on. There's a good chance you're right and there's no point frustrating yourself on it when there's plenty of more typical examples to practice on. And when you get bored with the adults, there's always the juveniles!
I hope this was useful and not too rambling. This is a topic I enjoy so don't hesitate to ask questions or share photos for feedback. Happy gulling!
