Getting to know Magellanic Penguins breeding in Staten Island: foraging behaviour and areas during chick rearing period

ROSCIANO NATALIA G.; PÜTZ, KLEMENS; RAYA REY ANDREA

Bristol

Congreso; 8th International Penguin Conference; 2013

Bristol University

Studies of the foraging behaviour of seabirds are important to establish their role in marine food webs. In Penguins, foraging behaviour is known to vary with locality, sex and stage of breeding. For the first time, we studied the foraging behaviour of Magellanic Penguins (Spheniscus magellanicus) breeding on Staten Island, Argentina, to evaluate differences in the foraging behaviour between sexes and to characterize the core areas of their distribution at sea. Fifteen Magellanic Penguins (PM) (8 males, 7 females) from the colony at Bahía Franklin were equipped with GPS data loggers during the early chick rearing period in December 2011. Also, blood samples were taken for stable isotope analyses. Foraging trip duration was 22.4+7.5 hs and all except one penguin performed overnight trips, where dive depths were around 9 m. No significant differences between sexes were found for either diving or feeding effort, except for diving depth and wiggle number per minute during the bottom phase, being higher in males compared with females. PM initially headed northwest and west towards their foraging areas, with a maximum distance from the colony of 35.4+7.6 km, covering a trajectory of 110.6+29.7 km. Foraging areas (95% kernel contour) occupied 629.8 km2 for females and 738.7 km2 for males, and females´ area overlapped with males´ by 74%, revealing no differences in the areas for both sexes. Core areas (50% kernel contour) were situated in rather shallow waters (bathymetry 94.5+60.9 m females, 74.8+51.1 m males) with a high primary production (chlorophyll a, 1.7+0.8 mg/m3 females, 1.8+0.4 mg/m3 males) and temperate sea surface temperatures (8.1+0.2ºC females, 8.2+0.2ºC males). Stable isotopes analysis revealed no significant differences between sexes either for δ15N (15.8+0.3? females, 15.6+0.2? males) or δ13C (-18.3+1.5? females, -17.2+0.7? males), thereby indicating no dietary differences or contrasting feeding areas between sexes during the study period. δ15N values were higher than those for Sprattus fueguensis, the preferred prey of PM, and δ13C values showed that PM foraged mostly inshore, which was confirmed by the GPS data that showed most positions along the Le Maire Straight near the coast of Tierra del Fuego. In comparison with the nearest PM colony in the Beagle Channel, PM breeding in Staten Island performed longer and overnight foraging trips and covered larger areas. Those differences may be due to the larger density of birds feeding in the area and thus intra- and/or interspecific competition since the Beagle Channel´s colony holds around 3,000 pairs while in Staten Island more than 100,000 PM pairs and about 120,000 Rockhopper Penguin pairs forage in nearby waters.