Apparent Hybrid Calidrid Sandpipers

South Beach, Chatham, Massachusetts: 7 June - 4 July 2008

Blair Nikula

The two calidrid sandpipers depicted below both appear to be hybrids, most likely Dunlin (Calidris alpina) X White-rumped Sandpiper (Calidris fuscicollis). One is in a rather bright alternate plumage, while the other is in a basic-type (1st alternate?) plumage. Both are intermediate in size between the two presumed parent species, but with a rather attenuated appearance (somewhat more so on the alternate-plumaged bird), reminiscent of a White-rumped, though in neither bird do the wings extend beyond the tail.

The all-black bills are distinctly longer than a White-rumped's but shorter and less drooped than any Dunlin present in the area. The bill of the basic-plumaged bird appears somewhat deeper at the base than that of the alternate-plumaged bird. The legs and feet are blackish, and one bird, at least, has no palmations between the toes.

The tail on the alternate-plumaged bird has dark down the center of the upper tail coverts, but the dark is interspersed with white (see photos below). Both birds have streaking/spotting across the tips of some of the lowermost upper tail coverts, similar in that respect to a White-rumped. On 21 June I heard the alternate-plumaged bird vocalize once as it took flight: a rather high, single noted, "cheep", not nearly as high pitched and sibilant as a White-rumped, nor as low and harsh as a Dunlin, somewhat like a Western Sandpiper.

The plumage of the basic-type bird puzzles me. I assume it's a one-year-old bird, but the plumage seems remarkably clean and unworn, with no evidence of any molt in progress. Other yearling shorebirds in this area are invariably worn and molting (including flight feathers) in June. Perhaps it's an older bird that simply isn't as bright (a female?).

This alternate-plumaged bird seems almost certainly to be the bird present in the same area last summer, photos of which can be seen at: http://picasaweb.google.com/offermann.jeffrey/HybridCalidris and at: http://gallery.mac.com/mattpgarvey#100415&bgcolor=black&view=grid.  Note the more advanced(?) plumage (i.e., much more rusty coloration dorsally) this year compare to last year.

Very similar birds were seen in Florida in May 2005 (http://oceanwanderers.com/WayneRichardson.Sandpiper.html) and on Long Island, NY, in early June 2007 (http://picasaweb.google.com/tixbirdz/CalidrisSandpiperAtPikeSBeachLongIslandNY23Jun2007).

Comments and speculation welcome; email Blair Nikula.  Thanks to Shaibal Mitra, Nick Bonomo, Matt Garvey, Ian Nisbet, Clive Minton, and Marshall Illiff for providing links and/or comments. All images below were taken with a Canon 20D and 100-400mm IS lens and are copyright 2008 Blair Nikula.

The following 7 images of the alternate plumaged bird were taken on 21 June.

Three flight shots showing the intermediate tail pattern.

The following 4 images of the alternate-plumaged bird were taken on 7 June 2008.

Presumed hybrid (left) with Semipalmated Sandpiper (right).

Two heavily cropped shots to show the lack of palmations in the toes.

Both presumed hybrids, the basic-plumaged (1st alternate?) bird on the right and the alternate-plumaged bird 2nd from right, with two Dunlin on the left. The following two images were taken on 21 June 2008.

Two presumed hybrids, with two Dunlin in background.

The photo above blown up to show the basic-plumaged bird in more detail.

The basic-plumaged bird taking off, showing the tail pattern.