Marine habitat use of Peruvian boobies: A geographic and oceanographic comparison between inshore and offshore islands

Foraging areas of Peruvian boobies (Sula variegata) from Isla Lobos de Tierra (LT, inshore) and Isla Lobos de Afuera (LA, offshore) were overlaid with concurrent data on wind patterns and remotely sensed hydrographic features to identify the main abiotic factors that affect booby distribution and to compare habitat use between birds from inshore and offshore islands. Birds used across winds and across headwinds when commuting to their feeding grounds and across tailwinds when returning to their colonies. This strategy increased flight speeds by 38-53 in relation to headwinds, probably resulting in a reduction in energy costs when birds returned to their nests with heavy loads of food. Sea surface temperature of the foraged and the available areas were similar around LT and LA. Boobies from LT fed over the continental shelf and alongshore in areas with chlorophyll a (Chl a) concentration higher than expected from a random distribution. Conversely, birds from LA never came inshore, feeding over the shelf break and in waters with concentrations of Chl a similar to those in the available area. Remote-sensing measurements of primary productivity predicted the distribution of Peruvian boobies only for LT. Plumes of enriched water alongshore are formed during the austral summer, favouring the aggregation of anchoveta (Engraulis ringens), the main prey of Peruvian boobies. Boobies from LA may have potentially foraged inshore in an area also used by birds from LT, but it is likely that competition for food and energy constraints to raise three-chick broods restricted foraging range to waters far from the mainland.