CARTER, H.R, SEALY, S.G., BURKETT, E.E. & PIATT, J.F. 2005. Biology and conservation of Xantus’s Murrelet: discovery, taxonomy, and distribution. Marine Ornithology 33: 81-87.

The biology of Xantus’s Murrelets (Synthliboramphus hypoleucus) is similar in many respects to better-studied Ancient Murrelets (S. antiquus), especially regarding morphology and the species' precocial mode of post-hatching development. It nests mainly in rock crevices but also under shrubs on islands in southern California, USA, and northwestern Baja California, Mexico (27^o to 34^o N). The species was discovered in 1859 by János Xántus. Two subspecies (S. h. hypoleucus and S. h. scrippsi) are recognized that show limited evidence of interbreeding. At sea, closely related Craveri’s Murrelets (S. craveri) co-occur with Xantus’s Murrelets off California and western Baja California during half the year, but the former species has a discrete breeding range in the Gulf of California, Mexico. Breeding was documented at 13 island groups between 1863 and 1976. Post-breeding dispersal as far north as central British Columbia, Canada (ca. 52^o N) was observed in the 1940s to 1960s. A few Xantus's Murrelets disperse south of breeding colonies to Magdalena Bay, Baja California (ca. 24^o N). The southernmost record is the type specimen collected by Xántus near Cabo San Lucas, Baja California (ca. 23^o N). Chief threats to this species include introduced mammalian predators on breeding islands, heightened predation by natural predators in human-modified island habitats, and oil pollution. In January 2005, a Pacific Seabird Group special symposium “Biology and conservation of the Xantus’s Murrelet” highlighted conservation concerns and promoted publication of recent studies of this little-known alcid, with 8 symposium papers published in this issue of Marine Ornithology. Much of what we know about Xantus’s Murrelets has been learned in recent years, and many aspects of biology remain to be described.

Keywords: Xantus’s Murrelet, Synthliboramphus hypoleucus, Craveri’s Murrelet, Synthliboramphus craveri, distribution, taxonomy, genus Endomychura