Sunday, July 3, 2011

Roseate Terns

Adult Roseate Tern on Eastern Egg Rock, Maine, in June 2011.
From Oak Harbor, Ohio, Kenn writes: Terns may be the ultimate summer birds. They are related to gulls, but gulls thrive in cold weather, some even spending the winter north of the Arctic Circle. Terns, by contrast, love warm climates. In much of North America, they are most prevalent during the summer.

About ten days ago, thanks to the generosity of Dr. Steve Kress and his highly successful Project Puffin, Kimberly and I were able to visit Eastern Egg Rock, in the Gulf of Maine. We did see puffins there, and many other birds as well; maybe Kim will blog about the puffins (hint, hint). But I was most pleased by the opportunity to look closely at Roseate Terns.

Some treatments of tern identification focus on bill color. The mostly-blackish bill of Roseate Tern can be useful for quick ID, but it’s tricky, too: other terns have blackish bills for part of the year, and in transitional stages they can show color patterns much like that of the Roseate’s bill. The SHAPE of the bill is a better confirming point. It’s relatively long, thick at the base and tapered to a fine tip, with the gonydeal angle on the lower mandible located fairly close to the base of the bill.

Wing pattern is one of the best ID points.  Summer adults typically have dark outer vanes on only the outer three primaries.  When the wing is folded, this shows up as a limited dark area on the wingtip.

Here’s a closeup of the wingtip from the previous photo.  Looking at the top of the near wing (the one on this side of the bird!), we can see dark gray on the three longest feathers, while the rest of the primaries (stacked up toward the left) are paler silvery gray.

The wing pattern can be even more obvious when the wings are spread.  In this photo, on the far wing, the dark gray is clearly limited to only the three longest primaries.  On the nearer wing, we can see that there is no dark trailing edge to the wing at all.

Compare that underwing pattern to the one shown by this Common Tern, photographed at the same place and date.  The black trailing edge to the outer primaries is obvious at a glance.

Adult Common Tern in flight, Eastern Egg Rock, Maine, in June 2011.
Roseate Tern also has a noticeably long tail, and lacks any black or gray on the tail (Common and Arctic terns both have narrow black outer vanes on the outer tail feathers, and Forster’s Tern shows some gray on the inner vanes).   The faint rosy blush on the breast feathers, the source of the bird’s name, is a fleeting phenomenon of spring, and barely a hint of it shows in our photos from late June.  Regardless, Roseate Tern is still a beautiful bird, and well worth the effort to find and identify!  For those with a keen interest in the subject, more information on identifying terns can be found in two chapters of my new Kaufman Field Guide to Advanced Birding. 

Roseate Tern is a widespread species, found from the North Atlantic to the Indian Ocean, but it is not abundant anywhere.  Its North American populations have declined seriously, so it is now listed as Endangered in the northeastern USA and eastern Canada, and as Threatened in the southeastern USA.   The nesting Roseates on Eastern Egg Rock (along with about equal numbers of Arctic Terns, and many more Common Terns) are closely monitored and protected by Project Puffin, a great program that deserves the support of birders everywhere.