Foraging distance affects reproductive success in Magellanic penguins

Abstract

Foraging distance affects reproductive success and other demographic parameters in seabirds and pinnipeds. We tracked breeding Magellanic penguins Spheniscus magellanicus at Punta Tombo, Argentina using satellite transmitters from 1996 to 2006 (n = 148 males, 57 females) to investigate the variability in foraging distance and its effects on reproductive success. The time a penguin was away from its nest predicted the distance it swam during all stages of the breeding season (p < 0.005); this relationship was linear during incubation and nonlinear during chick rearing. During incubation, penguins went 1.0 km farther from the colony for every additional hour they were away from the nest, and the distance penguins traveled predicted the mean colony reproductive success. When chicks were >30 d old, the probability of fledging 2 chicks was highest when penguins went less than 70 km from their nests. Penguins that went between 70 and 180 km from their nests were most likely to raise one chick, and the probability of losing both chicks increased with trip distance. Females and males made trips of similar distance. Foraging-trip distance varied within breeding season (p < 0.005). Penguins went farthest during incubation (411 ± 11.8 km), and stayed closest (61 ± 3.9 km) when chicks were <30 d old, requiring parents to guard them. When chicks were older, adults traveled 111 ± 5.0 km. Mean foraging-trip distance varied among years (p < 0.005) by factors of 1.5 to 1.8, and trips by an individual penguin varied by a factor of 22. © Inter-Research 2009.