A prominent phase of the annual cyle in migratory animals is the transition between migration and reproduction. The transition is a small part of the annual cycle, but details of its timing deserve attention. From a distant location, animals must initiate a long migration so that they arrive at the breeding ground on a precise schedule. Here we take advantage of a sample of female northern elephant seals that were tracked by satellite during their...

Long-term observations of foraging success at the population scale are key to understanding demographic and ecological patterns. Northern elephant seals, Mirounga angustirostris, are capital breeders and the resources delivered to the pup during the 4-week lactation period are related to both the past foraging success of the mother and the future survival of the pup post-weaning. We collected weight and basic morphometric data from more than 7,000 recently weaned elephant seals at the Año Nuevo...

Snow insulates the soil from air temperature, decreasing winter cold stress and altering energy use for organisms that overwinter in the soil. As climate change alters snowpack and air temperatures, it is critical to account for the role of snow in modulating vulnerability to winter climate change. Along elevational gradients in snowy mountains, snow cover increases but air temperature decreases, and it is unknown how these opposing gradients impact performance and fitness of organisms overwintering...

All organisms face resource limitations that will ultimately restrict population growth, but the controlling mechanisms vary across ecosystems, taxa, and reproductive strategies. Using four decades of data, we examine how variation in the environment and population density affect reproductive outcomes in a capital-breeding carnivore, the northern elephant seal (Mirounga angustirostris). This species provides a unique opportunity to examine the relative importance of resource acquisition and density-dependence on breeding success. Capital breeders accrue resources over large...