Nesting Waterbirds of Isla Montague, Northern Gulf of California, Mexico: Loss of Eggs Due to Predation and Flooding, 1993-1994

Abstract

-We studied seven species of waterbirds that nested on Isla Montague, Mexico, at the mouth of the Colorado River, during the 1993 and 1994 breeding seasons: Great Blue Heron (Ardea herodias), Snowy Egret (Egretta thula), Black-crowned Night Heron (Nycticorax nycticorax), Laughing Gull (Larus atricilla), Least Tern (Sterna antillarum), Gull-billed Tern (Sterna nilotica), and Black Skimmer (Rynchops niger). Breeding occurred along several tidal channels of the Estero del Chayo and on shell mounds near the lighthouse. There were low levels of predation, by at least one Coyote (Canis latrans), and unknown, but likely avian, predators. Tidal inundation was the major factor affecting the nesting of the birds, as it destroyed almost all nests, eggs and chicks on at least five occasions during one breeding season. It seems likely that the pattern of inundations we recorded does not happen all years. Received 21 August 2000, accepted 20 March 2001.