Not a bad response rate on this week’s quiz, and good variability in the guesses. First, a disclaimer: your blogger does not profess to be anything other than a self-taught student of dead bird identification, so the “answers” given here are by no means absolute, but only my own opinion based on the evidence.
There was nothing left of Bird A aside from a head and trailing spinal column. Guesses ranged from immature Great Black-Backed Gull or Herring Gull to Glaucous Gull. Your blogger’s answer: sure. Based on what we have for evidence, really any of those are possible. The first item to consider is the culmen length, which Diana reported as 64mm. This places it right in the overlap between numerous species of large gull. The only other clue we really have here is the coloration of the bill, and this, unfortunately, is not much more enlightening. From what we can see, the bill is mainly pale with a band of black near the tip. As you can see in the photos here, this coloration can occur in multiple species of gull.
Had we more to go on–the coloration of the head, some of the body, or even one wing, we could get a lot farther with this i.d. But for the purposes of the database, we must be conservative and classify Bird A, unsatisfyingly, as “large, immature gull.” Sigh.
2nd-3rd year Herring Gull: bill shows pale tip, then black band, then pale pink-gray base.
2nd year Great Black-Backed Gull. Note the bill, which looks strikingly similar to the Herring Gull of similar age.
2nd year Glaucous Gull. More of the same in terms of bill color.
Let’s see if we can’t do any better with Bird B. What we have to go on here is basically a gray wing with black primaries and rather large white mirrors (spots) on those primaries. Also, an all-white tail. And we know that the wing chord is only 32cm. Finally, I posit that there is a mangled, but bright yellow leg hanging off the pelvis on the right side of the photo. The leg aside (pun intended), let’s consider the wing alone for a moment.
Ring-billed Gull wing (adult). Black primaries with prominent white mirrors.
Laughing Gull wing (adult). White mirrors at wingtips can vary, but will generally be smaller than Ring-billed Gull's.
Black-legged Kittiwake wing (adult). Note characteristic "ink-dipped" appearance to primary tips.
These three species were offered as guesses on this quiz. From the photos here, you can see the variability in the amount of black on the primaries. Also, note that the division between gray and black is least defined in the Laughing Gull, more defined in the Ring-billed, and most stark in the Kittiwake. Bird B seems most to resemble the Ring-billed, and if you believe in the phantom yellow leg, that would seal the deal for Ring-billed Gull. One other note, without the yellow leg, and without the wing chord, this specimen would be basically indistinguishable from a Herring Gull, which has a nearly identical wing coloration.