Different migration strategies under warming ocean anomalies in penguins: A study of spatial, oceanographic, and isotopic niche segregation

Abstract

Many seabirds adjust migratory movements to interannual oceanic variability, tracking food resources, and potentially avoiding competition. This study examines the at-sea ecological niches of two penguin species, their overlap across years, and how environmental variability influences them. Over three years, we monitored Magellanic Penguins (Spheniscus magellanicus) and southern Rockhopper Penguins (Eudyptes chrysocome chrysocome), breeding sympatrically in Puerto Deseado (Argentina). During migration, spatial overlap was partial (42.94%), with species largely separated in two productive areas within the Argentine Shelf area, but both species occupied similar oceanographic niches (64% overlap) (Schoener’s D index). Despite interannual variation in sea surface temperature, Magellanic Penguins were consistently found within the same areas, resulting in annual changes in their oceanographic niches. In contrast, Rockhopper Penguins had a more dispersed distribution in years with a positive sea surface temperature anomaly, thereby increasing their interannual oceanographic niche overlap. Isotope analyses indicated distinct foraging niches, with Magellanic Penguins foraging less pelagically and at higher trophic levels than Rockhopper Penguins. Our findings suggest that Magellanic Penguins exhibit higher spatial consistency, while Rockhopper Penguins track their oceanographic niche more closely. Whether this indicates higher oceanographic niche flexibility in Magellanic Penguins and thus greater resilience to environmental change would require further research.