Nest-site characteristics and reproductive success in Magellanic Penguins (Spheniscus magellanicus)

Abstract

We used cross-sectional, longitudinal, and experimental data to investigate the effects of habitat at the smallest spatial scale - the nest site - on reproductive success of Magellanic Penguins (Spheniscus magellanicus). Over an eight-year period, the amount of nest cover was positively correlated with fledging success. The same pairs tended to be more successful when they had more nest cover, and experimental increases and decreases in cover significantly affected survival of nest contents. Other characteristics of nest sites, such as nest type and type of vegetation over the nest, did not affect success. The positive effect of cover resulted mainly from reduced exposure of nest contents to predators during incubation and to high temperatures when chicks were young. Roof cover was positively correlated with fledging success in nests from all areas. Cover on the sides of the nest giving the most protection from the sun was positively correlated with fledging success in warmer sites and with survival of young chicks in all areas. Young chicks at nests with less cover were more likely to move from their nests and to die on hot days. Experimental results indicated that the likelihood of egg detection by predators decreased with increasing nest cover. Height of nest entrance was a significant predictor of egg loss, suggesting that accessibility of nest contents to predators was an important component of predation risk. Thermal properties of nests and risk of predation were related; predation of nest contents was more likely when adults were absent, and during hot weather adults were more often absent from nests with little cover. Although the effect of cover on success was small relative to the large yearly variation in success due to food conditions, cover is likely to influence lifetime reproductive success substantially. Large and long-term data sets and experimental approaches may be necessary to identify subtle but biologically important factors among long-lived organisms that inhabit variable environments.