I caught this adult Swallow-tailed Gull reacting to the background spray from a spectacular blowhole. This strange gull breeds only on the Galapagos and on Malpelo Island, Columbia. It was originally thought to be sedentary, but migrates regularly south to Central Chile. In the Northern Hemisphere there are recent records off Costa Rica. A controversial record from Monterey, California 6-8 June 1985 was eventually accepted after being questioned with regard to its natural occurrence. There is also an accepted sight record from near the Farallon Islands in California. Away from the rocky cliffs where it nests, this is a pelagic species which feeds at night. We often saw them following our boat after dark. The recent 49th supplement to the AOU Checklist moves this species to the
front of the pack in the gull assemblage. This is based on genetic data (Pons et al. 2005) which suggest that it is a basal taxon within the Laridae. It is also different enough from other gulls to maintain it in its own genus, Creagrus. Canon PowerShot S3 IS
Reference:
PONS, J.-M., A. HASSANIN, AND P.-A. CROCHET. 2005. Phylogenetic relationships within the Laridae (Charadriiformes: Aves) inferred from mitochondrial markers. Molecular Phylogenetics & Evolution 37: 686-699.