BBB – Challenge of Identifying Juvenile Gulls

Can you identify these two species? Treman Marine Park, Ithaca, New York

Every birder knows what a LBB or LBJ is… Little Brown Bird or Little Brown Job… and birders understand the difficulty in identifying some of the small brown sparrows, flycatchers, warblers and more.

What about a BBB?  I’m talking Big Brown Birds, specifically young gulls in winter.

As mentioned earlier this month, one of my goals for this winter is to spend some time really studying the gulls in the area.  I have never paid close attention to the subtleties of identifying some of the less common gulls as they are very difficult and can be quite frustrating.

Take the two images above.  I will tell you now that not only are these are two different birds, they are two different species.  One is extremely common and one is rather rare.  I’ve spent the last three days looking through flocks of gulls carefully examining each and every one of the common birds to find the one single rare species, a Thayer’s Gull.

Read on to learn more about these two species and which one is which…

So which one is which?  The right bird is the ubiquitous Herring Gull (Larus argentatus) while the left bird is the rare Thayer’s Gull (Larus thayeri).  Easy right?  No?  Let’s break it down.

So both these birds are juveniles, meaning they both hatched this past summer.  Here is how I identified the Thayer’s Gull from among the dozen or so other Herring Gulls resting on the docks this morning.

Thayer's Gull (Larus thayeri) - Treman Marine Park, Ithaca, New York

First is the plumage.  The primary feathers (the main feathers used for flight and found on the tips of the wings extending backwards) are a black or very dark brown in the Herring Gull and light to dark brown in the Thayer’s Gull.  When the bird is at rest as shown here, the primaries are folded so they look a lot like a tail.  To locate these feathers look at the right image of the Herring Gull.  The bird appears to have three tails, two long pointed sections and one shorter section.  The two long pointed groups of feathers are actually the wing tips, not the tail, and these are the feathers to examine.  The Herring should be darker than the Thayer’s and the Thayer’s should be a tad lighter, but not as light as the body of the bird.  Yeah, I know, its tough and this isn’t the best image to show it in the Thayer’s so let’s move on.

Herring Gull (Larus argentatus) - Treman Marine Park, Ithaca, New York

Second let’s examine the structure of the bird.  Look at the shape of the head and bill.  The Thayer’s Gull has a more rounded, circular head while the Herring Gull’s head is more oblong.  To me, the Herring also has a heavier looking beak.  Ultimately, the Thayer’s Gull is built more like an Iceland Gull.  Two days ago I had never seen an Iceland Gull so that wouldn’t have helped me but after seeing one on Sunday I now understand the comparison.  Ultimately, in a flock of Herring Gulls, the Thayer does look structurally different.

Not convinced?  Well, I’ve spent a good portion of Sunday, Monday, and Tuesday staring at these birds.  It’s hard to explain in a single photo but I’m confident after watching this particular individual bird today, it is definitely not a Herring Gull and is the Thayer’s that has been seen in the area.

Just to complicate things even more, a possible hybrid (Glaucous x Herring) gull was reported in the same flock today.  I don’t even know where to begin trying to ID it.  The gulls open up a whole new world of identification challenges and it’s going to be an interesting winter.  So far I’ve already picked up two new species.  I bet I can get at least 3 more!

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  1. Drew,

    What is a species?

    Is a species a population of animals that is able to breed and produce viable offspring that can themselves breed? Is a species a population that compromises a genetically distinct lineage? Is a species a population that maintains an ecologically distinct role as compared to other populations?
    Is a species simply a population that is morphologically distinct (used to be)?

    For the sake of provocation…why do you all care about naming things that might not even be different? Nature is often about shades of grey…

  2. Greg,

    I like your line of questioning and I think I will be examining it in my Sunday Essay. Check back then!

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