PFISTER, T., PFISTER, B., JIMÉNEZ-SERRANÍA, V., DE-PEDRO-DÍAZ, D., SUÁREZ-GRACIDA, G., & DUBERSTEIN, J.N. 2006. Assessment of the Nesting Population of Double-crested Cormorants Phalacrocorax auritus albociliatus on Isla Alcatraz, Gulf of California, México. Marine Ornithology 33: 195-197.

In the early 1970s, censuses of Double-crested Cormorants Phalacrocorax auritus albociliatus were conducted on Isla Alcatraz in the Gulf of California, which suggested that Isla Alcatraz was one of the largest Double-crested Cormorant nesting colonies in the Gulf. To update information on the size of the colony, we counted active nests at Isla Alcatraz during the 2000–2001, 2001–2002, and 2002–2003 seasons. Nesting began in September and continued through April. Peak nesting activity in 2000–2001 was in early January, with 1225 active nests, in 2001-2002 the peak was recorded in late November (1093 active nests) and in 2002–2003 the peak occurred again in late November (1683 active nests). Based on previous population estimates for Pacific coast nesting pairs of Double-crested Cormorants, 30-40% of the coastal nesting population of P. a. albociliatus in the Gulf of California nested on Isla Alcatraz during the three seasons; representing 5-8 % of the overall Pacific coast nesting population. Although Isla Alcatraz is protected under the Gulf of California Island Reserve program, we believe that additional protection should be afforded to Isla Alcatraz to ensure the future success of this important colony.

Key words: Double-crested Cormorant, Phalacrocorax auritus albociliatus, Gulf of California, seabird breeding colony, nesting pairs, island management