Shifting predator–prey dynamics at the land–sea interface: The case of Magellanic penguins and pumas

• Pumas caused measurable penguin mortality and can slow population growth. • Field data revealed surplus killing, with many carcasses only partly consumed. • Population models were most sensitive to juvenile survival and breeding success. • Extinction risk rose only under poor reproduction and low juvenile survival. The expansion of Magellanic penguins into mainland territory in Argentina is providing a new prey to recovering puma populations. This dietary shift was first reported about 20 years ago, but its extent remains poorly studied. Here, we present a comprehensive analysis of puma predation on penguins in Monte León National Park (MLNP), in Argentinian Patagonia, and explore its effects on this breeding population. We analysed puma predation over four consecutive breeding seasons (2007–2010) and modelled the demography of the colony under different reproductive success, juvenile survival, and puma-induced mortality rates, to test whether sustained mortality could compromise its long-term persistence. We estimated that, during our study, 7,087 adult penguins were killed in total, representing a cumulative 7,60 % of the breeding population. Puma predation occurred throughout the entire colony, with hotspots on the southern and northern edges, and included events of surplus killing. Demographically, the population was most sensitive to variations in juvenile survival and reproductive success. Regardless of the predation level, low reproductive success combined with low or medium juvenile survival led to extinction within 100 years. Puma predation lowered population growth but did not cause colony extinction; substantial reductions occurred under medium reproductive success with low juvenile survival, or low reproductive success with high juvenile survival. These findings highlight a broader conservation concern: the growing vulnerability of mainland seabird colonies to terrestrial predator expansion. We recommend sustained monitoring of this and other colonies to detect early demographic declines and inform management actions to mitigate excessive puma predation.