Keitt, B.S. 2005. Status of Xantus’s Murrelet and its nesting habitat in Baja California, Mexico. Marine Ornithology 33: 105-114.

A preliminary survey was conducted in 1999 to establish the status of the Xantus’s Murrelet (Synthliboramphus hypoleucus) in Baja California, Mexico. Seven island groups with prior evidence of breeding (Coronado, Todos Santos, San Martín, San Jerónimo, San Benito, Asuncíon, and San Roque) and two potential breeding islands without prior evidence of nesting (Natividad, Adelaida) were examined. In 2004, additional work was conducted at Zapato Islet off Guadalupe Island. Presence of murrelets was detected through nest searches and by rough estimation of birds in nocturnal at-sea congregations using boat-based and land-based vocalization counts. Vocalizations were heard at six island groups (Coronado, Todos Santos, San Martín, San Jerónimo, San Benito, and Guadalupe) and nests were found at four island groups (Coronado, San Jerónimo, San Benito, and Guadalupe). Both land-based and boat-based vocalization surveys detected presence or apparent absence of murrelets at potential nesting islands, though boat-based vocalization rates were higher on average. Vocalization surveys cannot readily be converted to breeding population estimates, but overall population size of murrelets in Baja California appears to about 2,300 pairs (range 1,000 - 4,000 pairs), similar to previous estimates. Historically, nonindigenous mammals were introduced to most islands in Baja California; recent progress in removing introduced mammals should benefit Xantus’s Murrelets.

Key words: Baja California, conservation, nesting habitat, predation, status survey, Synthliboramphus hypoleucus, Xantus’s Murrelet