Ladies and gentlemen, I present to you ... immature gulls! Cue the sound of everyone closing their browser window.
First is a juvenile Lesser Black-backed from Tiscornia.
Fifteen years ago I doubt I could have appreciated the difference between this and a Herring Gull, but they've gotten a lot more common.
The bill is smaller than a Herring Gull's and stays darker much longer (more later). In flight notice how all of the primary feathers are pretty solidly dark.
Contrast those flight feathers with this Herring Gull's.
The outer primaries are dark, the inner primaries are a much lighter gray-brown. The above Herring still has an all dark bill and probably is from much farther north than this next bird which is more typical of our Herrings which is well on its way to a two-toned bill (and is also getting some first winter feathers in the mantle).
Here's a first year Lesser Black-backed from New Buffalo with a similarly aged Herring behind.
I wouldn't make a huge deal out of how much darker the Lesser is; that difference is accentuated by the Herring being a couple months older as evidenced by the two-toned bill. The Herring is a lot more faded and its brown juvenile feathers have had probably twice as much time to fade. A juvenile Lesser is more crisply marked than a juvenile Herring, but this Herring isn't a juvie any more, it's working its way into first winter.
Just for fun here's the above Lesser now facing right with a 2nd winter Lesser in front of it.
The 2nd winter Lesser has a darker bill than the first fall Herring. You can start to get a hint of the darker mantle. The tertials (darker feathers with the bright white ends just short of the primaries) are pretty classic for 2nd winter Lesser Black-backed too.
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