| Summary: | Arrecife Alacranes, the northernmost reef zone of the Gulf of Mexico, harbors the largest nesting seabird concentrations of the region (ca. 70,000 nests), and is a Mexican federal protected area. Some important threats to the area are oil extraction, introduced species (main cause of extinction in islands), fisheries, and tourism. Black rats (Rattus rattus) and casuarina trees occur in Isla Perez, one of the reef’s islands, and a plan for the rodent eradication is under way. The last seabird census reported was done in 1986. In May and August 2009 we made surveys to monitor their present populations. Direct nest counts were carried out, with complementary counts on photographs. The total nests found per island were: Perez: 139,116 Sterna fuscata, 1,039 Anous stolidus; Muertos: 827 Sula dactylatra, 10 S.sula, 50 Fregata magnificens; Pájaros: 64 S.dactylatra; Chica: 22 S.dactylatra; Desterrada: 82 S.leucogaster. Our information revealed much larger numbers than those previously reported for S. fuscata, S. dactylatra, and S. sula, but less for F. magnificens. Protection of the area could be one factor to explain the increment in the seabird nesting numbers, and it will be interesting to see what changes occur after the rodent eradication is carried out, but also, effects of the BP oil spill may be detected.
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