Saturday, June 4, 2022

Swallow-Tailed Gull

One of the birds I most wanted to see in the Galapagos Islands was the swallow-tailed gull. It is the only gull in the world, in fact, the only seabird, that is fully nocturnal. It feeds on squid and small fish at night that rise to the surface of the ocean to eat plankton. It has structural differences that aid the night feeding: Its eyes are larger in size and volume than the eyes of any other gull; and they also have a layer of tissue in the back of the eye that reflects light back through the retina increasing the amount of light available to the photo receptor cells. 
It is near-endemic to the Galapagos Islands for breeding, that is all of them breed in the Galapagos Islands except a few pair that breed on Malpelo Island off the coast of Colombia. In the Galapagos the greatest numbers breed on the rocky shores and cliffs of Hood, Tower and Wolf Islands and it is more common on the eastern islands where the water is warmer. When not breeding it is completely pelagic, meaning that it spends all of its time on and over the ocean, usually further east toward the coasts of Ecuador and Peru and as far south as central Chile. It is not likely to be seen from land. We saw our first swallow-tailed gull on a cliff in Vicente Roca Point

and then had our best views with lots of them along the coast of Santiago Island.

They are beautiful: during breeding they are a pearly gray with a bluish/black head; a black eye with a red eye-ring, a bluish/black bill with a pale-white tip and a white spot at the base; when not breeding they have a white head with thick black mascara around the eye.  
Juveniles are similar to non-breeding adults, but are darker above with a scaly pattern and an entirely black bill.

1 comment:

  1. I'm surprised there aren't more nocturnal seabirds. It seems like a great time to feed.