Friday, March 4, 2011

Magnificent Frigatebird

In the United States, Magnificent Frigatebirds only breed in the Dry Tortugas.  The breed elsewhere in the Caribbean and also in various locations in the Pacific.  Frigatebirds wander regularly to North Carolina and the shores of the Gulf of Mexico.  Hurricanes blow them further astray, often considerable distances inland.  Several frigatebirds have even been recorded in Minnesota.
When we visited the Dry Tortugas in February, we watched this juvenile bird catch a small fish from the sea surface. (Frigatebirds never land in the water--they are not very waterproof.)  This bird did a curious thing.  The bird dropped its fish, and then swooped down and recaptured it, only to drop it again.  Was this some short of practice fishing?  Or playing?  Later in Key West, we saw a male frigatebird high in the air toss a fish to a female flying below it.  The female caught the fish.  So perhaps the frigatebird we saw in the Dry Tortugas was practicing some sort of mating behavior.
Frigatebirds have the longest wingspan in proportion to weight of all birds (Dunn and Alderfer 2006). Notice this male frigatebird's red throat pouch.
Male frigate birds form displaying groups (leks) and attract females by inflating their throat pouches.  The birds below are from the Galapagos Islands.  Notice that the female Magnificent Frigatebird has a dark head and a white lower breast, unlike the juvenile in the first two photographs in this post.  Females lay only one egg. Apparently males abandon their families after the young are half-grown, and are able to produce a second young with a new mate while their first female cares of the initial hatchling (Diamond and Schreiber 2002).

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