Sex-specific foraging behaviour in a monomorphic seabird

Abstract

Sexual differences in the foraging behaviour of parents have been observed in a number of sexually sizedimorphic birds, particularly seabirds, and the usual inference has been that these sex-specific differences are mediated primarily by differences in body size. To test this explanation, we compared the foraging behaviour of parents in a monomorphic seabird species, the northern gannet Morus bassanus. Using specially designed instruments and radio telemetry we found that individuals of both sexes were consistent in the directions and durations of their foraging trips. However, there were significant differences in the foraging behaviour of males and females. Female gannets were not only more selective than males in the areas where they foraged, but they also made longer, deeper dives and spent more time on the sea surface than males. As the sexes are morphologically similar in this species, then these differences are unlikely to have been mediated by body size. Our work highlights the need to investigate sexual differences in the foraging behaviour of seabirds and other species more closely, in order to test alternative theories that do not rely on differences in body size.

Foraging areas of streaked shearwaters in relation to seasonal changes in the marine environment of the Northwestern Pacific: inter-colony and sex-related differences

“…Sex-related differences in foraging areas are commonly observed among flying seabirds, and have been attributed to the differences in flight morphology or to differing reproductive roles between the sexes (González-Solís et al 2000, Shaffer et al 2001, Lewis et al 2002, Phillips et al 2004b. Although male streaked shearwaters are 1.2 times heavier and have larger bodies than females (Arima & Sugawa 2004, Ochi et al 2010, foraging areas differed between the sexes only during pre-laying and not during incubation.…”

Foraging distance affects reproductive success in Magellanic penguins

“…This is often linked to sexual size dimorphism, but also occurs in species with males and females of similar size (Lewis et al 2002). Male Magellanic penguins are slightly larger than females and are at sea a few weeks earlier during incubation (Boersma et al 1990).…”

Flexible foraging behaviour of a sexually dimorphic seabird: large males do not always dive deep

“…thick-billed murres Uria lomvia: Woo et al 1999; northern gannets Morus bassanus: Lewis et al 2002; common guillemots Uria aalge: Thaxter et al 2009). These differences are unlikely to have been mediated by body size, and could alternatively be explained by avoidance of inter-sexual competition for food.…”