CONICET | Buscador de Institutos y Recursos Humanos

The Magellanic penguin Spheniscus magellanicus is a top predator and a major consumerof marine resources in the Patagonian Continental Shelf and worldwide. It isthe most migratory of the Spheniscus penguins, but until recently, its migration routewas only partially known. Our aims with regard to the Magellanic penguin breedingon Isla Quiroga, Argentina, were: 1) to compare the distribution during the winterperiod between sexes and 2) in case that habitat is segregated, to evaluate possible proximatecauses like competitive exclusion and/or habitat specialization. In March 2017and 2018, prior to migration, we equipped 26 penguins with MK3/4 geolocators,which were recovered in late September/early October. Penguins dispersed northwardsup to 29°S and southwards up to 56°S, near the Beagle Channel, being distributedover 2158 ± 50 km of latitudinal range and showing a large-scale distribution patternacross longitudes in waters within the continental shelf. We found a longitudinal segregationbetween sexes in their winter grounds, with males closer to the 200-m isobathand further from the coastline than females. Morphological and physiological differencesbetween sexes might allow males to dive deeper at a lower cost than females,which could result in a more offshore path for males. This spatial segregation wassupported by bulk blood stable isotope values and estimated isotopic niche, whichdiffered between males and females at their arrival from winter breeding grounds, butnot while penguin breed and behave as central place foragers in the colony. For thefirst time in this species, we combined two independent tools, geolocation and stableisotope data, and find that sexual segregation in habitat use could potentially generatean optimal winter foraging strategy for both sexes, precluding potential intersexcompetition for food.