Population dynamics of the Galapagos flightless cormorant Phalacrocorax harrisi in relation to sea temperature

The Flightless Cormorant Phalacrocorax harrisi is restricted to c. 400 km of the western coastline of the Galápagos archipelago, coinciding with the local occurrence of seasonal upwelling oceanic currents. Here we report data from a 10-year historical study of a colony of c. 11 8 adult birds stretching c. 2 km along the coastline and representing about 12 % of the total population of the species. The number of clutches laid and juveniles fledged were positively associated with the persistence of cold nutrient-rich surface water in offshore foraging grounds, suggesting that availability of food brought about by changes in marine productivity is both the proximate and ultimate factor controlling the timing and outcome of breeding. Individuals frequently made more than one breeding attempt per year, usually changing mates. Males invested more in nest-building and feeding of the offspring than their mates, and we relate this to male and female reproductive strategies. Most Flightless Cormorants were extremely sedentary, having attachments to local stretches of coastline several hundred metres long. However, a few birds travelled many kilometres, sometimes between colonies. Adult survival and condition was not associated with breeding effort or success. Adult survival, recruitment through births and minimal net immigration validate a published demographic model of the species (Valle 1995).