Winter dispersal of Magellanic penguins at Martillo Island: Sexual differences in movement patterns and trophic ecology

Abstract

The dispersal of penguins during the non-breeding period is a critical period that can affect breeding success and survival in the following season. Thus, knowledge of penguin foraging ecology during this energy-intensive period is crucial to understand their responses to ecosystem variability. We recorded winter dispersal of Magellanic penguins Spheniscus magellanicus from Martillo Island (Beagle Channel, Argentina) using LAT2900 geolocators in 2017. We collected whole blood samples when the penguins first arrived at the colony in spring to study their pre-breeding foraging niche using stable carbon (δ13C) and nitrogen (δ15N) isotope analysis. In total, 26 adults were equipped after their annual molt, of which 24 were re-captured. However, only 20 were still equipped with devices and only 9 datasets could be recovered successfully. We found that penguins dispersed north along the Patagonian coast up to just south of Buenos Aires, Argentina (<38°S). In addition, prior to their return to the breeding site (August-September), females were mainly concentrated in more southern waters (between 49° S to 55°S) relative to males (between 41°S to 45°S). We also observed a significant difference between sexes in δ13C (W= 25, p<0.05) but not in δ15N values (W= 53, p>0.05), with females also having larger isotopic foraging niche widths (SEAb) relative to males. Differences in the spatial distribution and isotopic values between sexes likely reflect a pattern of niche partitioning during the non-breeding period. These results provide insights into mechanisms that may reduce intraspecific competition and can possibly inform sex-specific conservation strategies during the non-breeding period.