Gulling season is getting off to a rather slow start in much of our area, but things are starting to pick up. One of the most sought after vagrant gulls east of the Rocky Mountains is Mew Gull. Here’s a little primer to help you pick one out of a flock of Ring-bills.
First cycle: These can be ridiculously difficult to tell apart. If you can see them fly, the dark tail of the Mew is your best mark. If they are sitting, you need to look at the pattern of the individual median upperwing coverts. Ring-billed has a distinctly pointed tip to the dark center of the individual feathers. Mew has dark feathers with a thin pale fringe, which creates a more solid pattern (less checkered) than Ring-billed. Additionally, Mew Gulls tend to be more heavily marked, especially on the underparts than Ring-billed, have smaller bills and often have a more “gentle” expression, caused by the combination of smaller bill, rounder head and larger dark eye.
Second year: The field guides note that Mew Gull often has bluish legs and base of the bill, and dark eyes in it’s second year. But Ring-billed can show all those features, too. Note the MEGU’s smaller bill and larger eye, creating a more “gentle” expression. Note also the larger tertial crescent and darker mantle.
Adults: the thing that stands out the most (for me) besides the small all-yellow bill, is the size of the tertial and secondary crescents. The back color can be very difficult to ascertain, and if the birds are sleeping, you can’t see the bill or the eyes. Scanning a flock of Ring-bills, I try to look at the tertial crescent of every adult bird.
But, even if you’re close it can be very difficult to pick out a Mew Gull in a flock of Ring-billed, especially an adult. Here’s a picture with a California Gull in the foreground, a Ring-billed Gull center and a Mew Gull at rear:
Note how the color and tone of the mantle of the Ring-billed is obviously lighter than the other two birds.The difference in tertial crescents is also easily seen, and picking out the Mew Gull is pretty easy. But what happens if the sun come out, and the birds shift position just a bit?
The difference is nowhere near as obvious. Sure, now that you know what to look for, you can pick out the Mew. Here’s another shot showing how low, winter light can mess with the impression of gull mantles:
But also notice how even in harsh, low light, the difference in tertial crescents can be seen. For my money, this is the best way to initially pick an adult Mew out of a flock of Ring-billed Gulls.
Share on Facebook