Relationship between reversed sexual dimorphism, breeding investment and foraging ecology in a pelagic seabird, the masked booby

Abstract

Reversed sexual dimorphism (RSD) may be related to different roles in breeding investment and/or foraging, but little information is available on foraging ecology. We studied the foraging behaviour and parental investment by male and female masked boobies, a species with RSD, by combining studies of foraging ecology using miniaturised activity and GPS data loggers of nest attendance, with an experimental study where flight costs were increased. Males attended the chick more often than females, but females provided more food to the chick than males. Males and females foraged during similar periods of the day, had similar prey types and sizes, diving depths, durations of foraging trips, foraging zones and ranges. Females spent a smaller proportion of the foraging trip sitting on the water and had higher diving rate than males, suggesting higher foraging effort by females. In females, trip duration correlated with mass at departure, suggesting a flexible investment through control by body mass. The experimental study showed that handicapped females and female partners of handicapped males lost mass compared to control birds, whereas there was no difference for males. These results indicate that the larger female is the main provisioner of the chick in the pair, and regulates breeding effort in relation to its own body mass, whereas males have a fixed investment. The different breeding investment between the sexes is associated with contrasting foraging strategies, but no clear niche differentiation was observed. The larger size of the females may be advantageous for provisioning the chick with large quantities of energy and for flexible breeding effort, while the smaller male invests in territory defence and nest guarding, a crucial task when breeding at high densities. In masked boobies, division of labour appears to be maximal during chick rearin-g-the most energy-demanding period--and may be related to evolution of RSD.

Variability of resource partitioning in sympatric tropical boobies

“…In this case, differences in foraging behaviour between sexes are related to breeding involvement, rather than influenced by competitive interactions for resources. This is consistent with previous research on masked and red-footed boobies in lowproductivity environments; no sex-related differences in diet were found for masked boobies at Clipperton Island (Weimerskirch et al 2009b) and Palmyra Atoll (Young et al 2010b), or for red-footed boobies at Europa Island (Weimers kirch et al 2006) and Palmyra Atoll (Young et al 2010b).…”

“…Given the larger body size of masked boobies compared to red-footed boobies (Young et al 2010b) and the importance of body size in structuring at-sea competitive interactions (Ballance et al 1997, González-Solís et al 2000, we expected to see significant resource partitioning between species at Tromelin Island. Despite the presence of reversed sexual dimorphism in both species (Weimerskirch et al 2006(Weimerskirch et al , 2009b, Young et al (2010b) did not find evidence of resource partitioning between sexes in either of these species. We therefore sought to investigate whether or not resource partitioning might occur between sexes in a more extreme oligo trophic environment.…”

“…Summary and statistical differences between the diets of masked (12 regurgitates; 91 prey items) and red-footed (13 regurgitates; 94 prey items) boobies at Tromelin Island. Values are mean ± SD ences in foraging range and trip duration (Weimerskirch et al 2009b), but other differences in foraging activity were evident. A study of sympatric bluefooted (Sula nebouxii) and brown (S. leucogaster brewsteri ) boobies in the Gulf of California (Weimerskirch et al 2009c), however, demonstrated greater sex-specific than species-specific differences in foraging behaviour.…”

“…Masked boobies at Tromelin Island (224 breeding pairs) had longer trip durations and greater maximum foraging ranges than at Palmyra Atoll (Young et al 2010b) but smaller maximum ranges than at Clipperton Island (Weimerskirch et al 2009b), the largest masked booby colony in the world (60 000 breeding pairs; Weimerskirch et al 2009a). Differences in intraspecific competition due to colony size could account for differences in maximum ranges of masked boobies observed at these 3 sites.…”

Foraging in Guanay cormorant and Peruvian booby, the major guano-producing seabirds in the Humboldt Current System

“…Boobies are well known to display a reversed sexual dimorphism (Nelson 1978), and several studies have found sex differences in foraging behaviour in several species (Lewis et al 2005, Zavalaga et al 2007, Weimerskirch et al 2009a and have suggested that they are related to the extent that sexual dimorphism exists for some foraging features, such as dive depths or foraging duration, or to different roles in parental investment. The only significant difference was the slightly longer foraging range of males versus females, a trend found in other species of boobies (Weimerskirch et al 2005(Weimerskirch et al , 2009a. These results suggest that in the case of abundant food, such as Peruvian anchovies in the HCS, sex-specific differences in foraging behaviour do not occur.…”