Friday, October 5, 2012

"Fri-D" - Caspian and Royal Terns

 [Caspian Tern, Nummy Island, Stone Harbor NJ, October 3 2012. Click to enlarge photos.]

If you wander about Stone Harbor Point, NJ, or other coastal points, this time of year, you'll find both of our large terns, Caspian and Royal. I happened to be standing on the free bridge north of Nummy Island, south of Stone Harbor, NJ last night (where I stand more than a habitat use analysis would statisically predict) and had mainly Caspians flying around, but some Royals, too. The bird above, a Caspian, identified itself with its sheet-ripping, scraping call, but its forehead seemed very white. Caspians are supposed to show at least dark stippling on the forehead year round, while Royals go most of the year with clean white foreheads, save when they are high-breeding plumage in early summer and have dark caps.

This is a good time to point out that just because you don't see a bird's field mark, it doesn't mean it isn't there. Like, this Caspian had dark stippling on the forehead (photo zoomed below) but you couldn't see it at a distance.

 [Same Caspian Tern showing dark stippling on the forehead, not evident at a distance.]

Compare the Royal Tern close-up below for the forehead pattern difference, and while you're at it, compare the bill color and size. The bill is slimmer than Caspian's - maybe hard to see with a fish in the way.

[Royal Tern showing white forehead, and thinner, oranger bill than Caspian.]

There are plenty of differences between Caspian and Royal Terns, from the calls (Caspians rasping and ripping to Royal's liquid ripppling) to the overall jizz of the birds, which is dramatically different. In a nutshell, Royal's are slim, thin and long-winged, Caspians are bulky broader-winged. Royals tend to inhabit beach and offshore, while Caspians are more likely to be seen over beach or inland, though there is plenty of overlap.

[Royal Tern. Note how the underwing tip is mostly white, with a dark trailing edge. Caspians have dark "mittens."]

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