Geolocation and stable isotopes indicate habitat segregation between sexes in Magellanic penguins during the winter dispersion

Abstract

The Magellanic penguin Spheniscus magellanicus is a top predator and a major consumer of marine resources in the Patagonian Continental Shelf and worldwide. It is the most migratory of the Spheniscus penguins, but until recently, its migration route was only partially known. Our aims with regard to the Magellanic penguin breeding on Isla Quiroga, Argentina, were: 1) to compare the distribution during the winter period between sexes and 2) in case that habitat is segregated, to evaluate possible proximate causes like competitive exclusion and/or habitat specialization. In March 2017 and 2018, prior to migration, we equipped 26 penguins with MK3/4 geolocators, which were recovered in late September/early October. Penguins dispersed northwards up to 29°S and southwards up to 56°S, near the Beagle Channel, being distributed over 2158 ± 50 km of latitudinal range and showing a large‐scale distribution pattern across longitudes in waters within the continental shelf. We found a longitudinal segregation between sexes in their winter grounds, with males closer to the 200‐m isobath and further from the coastline than females. Morphological and physiological differences between 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 was supported by bulk blood stable isotope values and estimated isotopic niche, which differed between males and females at their arrival from winter breeding grounds, but not while penguin breed and behave as central place foragers in the colony. For the first time in this species, we combined two independent tools, geolocation and stable isotope data, and find that sexual segregation in habitat use could potentially generate an optimal winter foraging strategy for both sexes, precluding potential intersex competition for food.

Sex-specific spatial use of the winter foraging areas by Magellanic penguins and assessment of potential conflicts with fisheries during winter dispersal

“…In this sense, also during May to August, females Magellanic penguins from Cabo dos Bahías colony were mainly found further north than males [17]. In contrast, Magellanic penguins from Quiroga Island presented spatial sexual segregation but at a longitudinal level (east-west), where males were found farther from the coast than females [18]. Once again, we find similarities in the movement patterns between Cabo dos Bahías and Martillo Island and contrasting differences with Quiroga Island.…”

“…We have no GLS data for this individual, however, in light of the integrity of the sample, this individual could be feeding in a different foraging area or even on different prey with respect to the rest of females, which has a direct influence on it blood isotope values. Females' showing a wider isotopic niche during the last month of the winter dispersal were also recorded at Quiroga Island colony [18]. In addition, the trophic position estimated for Martillo Island males' showed high values during this period, which could be correlated to a diet composition dominated by high trophic position organisms and/or benthic prey, such as squid (e.g.…”

“…As most seabirds, Magellanic penguins expand their spatial range for foraging during the non-breeding season. Coherently, the tracked individuals used an extensive area of the PS as reported for individuals tagged in northern colonies [17,18]. We detected spatial overlap with bottom trawl fishery during the whole range of their winter dispersal and with shrimp fishery from May to September.…”

“…The winter dispersal depicted in this study differed from the dispersal from northern colonies. Cabo dos Bahías penguins (44˚56 'S, 65˚33'W, [17]) used areas further north, while Quiroga Island penguins (47˚45 'S, 65˚53'W, [18]) presented two strategies, some moving north and others moving southwards from their colony. In this sense, our results show an interesting staggering phenomenon, with Martillo penguins moving northwards into areas utilized by individuals from northerly colonies during the breeding period, which themselves moved further north for their winter dispersion.…”

“…Three studies have focused on this species winter dispersal in the PS so far. Two studies in Northern Patagonia have successfully recorded Magellanic penguin throughout their whole winter dispersal and reported differences in the spatial use between sexes [17,18] but no differences in trophic position based on blood tissue δ 15 N values [18]. While in southern Patagonia, winter dispersal was recorded from March to June and showed no differences in spatial use by sex during those months [19].…”