Monday, January 7, 2013

Answer to Bird Quiz #158 - Great Black-backed Gull

As always having a gull for the weekly bird quiz cause people some trouble. We had 8 correct answers and 8 incorrect answers.

Last Week's Quiz:


How to Identify:

Although it was easy to identify the bird in this photo as a gull, getting it down to species proved to be much harder. Even though the lighting is poor, it is evident that the upperwings and mantle are extremely dark. The dark upperwings and mantle help us eliminate all of the lighter winged species such as California, Glaucous, Ring-billed, etc.  Also, despite the fact that there is nothing in the photo to use as a reference for the size of the bird, we can tell that it is a fairly bulky bird due to the broad wing bases, large head in comparison to body, and large bill. The large dark-backed gulls that we should consider in the US are Slaty-backed, Western, Yellow-footed, Lesser Black-backed, and Great Black-backed.  We can see the inner primaries seem to be molting/growing; so much of the wing pattern is not very useful unless we take molt into consideration.  We can eliminate Lesser Black-backed and Slaty-backed due to lack of streaking on the head and neck.  We can also eliminated Yellow-footed and Western due to a couple of features.  First, the head and bill of our bird are large and bulky compared to the body, more so than Western or Yellow-footed; this can be a tough feature to use unless you have lots of experience.  But we can also use wing pattern; the feathers that are growing in have fairly narrow white tips where the Western and Yellow-footed would have much wider white tips.  Also, on average, Great Black-backed have the darkest mantle and upperwings of any gull in the United States; our bird appears very dark which supports the identity of Great Black-backed Gull.

Next Quiz:

The second quiz in this month's series can be found here: http://nuttybirder.com/BirdQuiz/birdquiz.html#.UOte_m9z6So

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