Magellanic Penguin colonies: Detriments and benefits of predators and scavengers

Abstract

Terrestrial predation is a significant factor limiting the breeding success and shaping the abundance and distribution of penguin colonies. Conversely, these aggregations of seabirds can act as concentrate resource pulses, potentially enhancing local biodiversity by supporting diverse predators and scavenger communities. This study investigated the influence of predator community structure on the distribution of Magellanic penguin (Spheniscus magellanicus) colonies and assessed the impact of predation on breeding success, alongside the colony’ effect on predators and scavengers, at a central Patagonian colony (44°54´50.3"S, 65°32´46.8"W). A strong association was found between the occurrence of colonies and islands naturally lacking terrestrial mammal predators of adults, with 82% of known colonies situated in such predator-free environments. These mammalian predators double the potential interacting species richness in mainland colonies. In the focal colony, predation was the primary driver of reduced reproductive success, with the most impactful predators, in terms of losses, generally being the most abundant. Abundant predators were also frequent scavengers, although scavenging interactions exhibited greater species richness. Notably, predator and scavenger abundance increase 15-fold within the colony, demonstrating the penguin’s strong capacity to modulate local terrestrial communities. These findings reveal significant geographic variations in predator complexity affecting Magellanic penguins and highlight the crucial ecological role of their breeding colonies in supporting local predators and scavengers populations, highlighting their importance as key prey and ecosystem engineers in coastal environments.