Occasional inter-sex differences in diet and foraging behavior of the Blue-footed Booby: maximizing chick rearing in a variable environment?

Abstract

Labor division in parental care and reduction of inter-sex competition by division of the foraging niche have been suggested as part of the evolutionary basis for reversed sexual size dimorphism in boobies (Sulidae). To test the potential viability of both hypotheses for the maintenance of dimorphism, we studied parental care and foraging behavior of the Blue-footed Booby (Sula nebouxii) in two colonies in the Gulf of California, Mexico. Proportion of time spent at the nest, feeding frequency, and time devoted to nest defense were used as indicators of parental care. Foraging ecology was evaluated through the number and duration of foraging trips, proportion of time dedicated to flight and to active feeding, rate and depth of diving, and diet. We found some inter-sex differences in foraging only under high demand conditions, such as food shortage or large broods. Inconsistent inter-sex differences seem to be part of a strategy to maximize chick rearing under a variable environmental regime.

Lead, cadmium and mercury in the blood of the blue-footed booby (Sula nebouxii) from the coast of Sinaloa, Gulf of California, Mexico

“…The possible Hg excretion through eggs seems not enough to explain the sex-related difference in Hg blood concentrations. Inter-sex diet differences have been reported for Blue-footed Booby, females can consume larger fishes than males (Castillo-Guerrero and Mellink, 2011;Zavalaga et al, 2007) which was expected to derive in larger Hg concentrations, the opposite to results. At the same study site, with the use of stable isotopes, the δ 15 N values (indicator of trophic position of consumers, Bearhop et al, 2004) showed a similar temporal pattern between sexes: nitrogen isotope values of adults became more enriched in 15N after the offspring hatched, with males more enriched than females during some periods (González-Medina, 2016).…”

“…The Blue-footed Booby is a sexually dimorphic seabird, with females heavier (30-32%) and larger (5-10%) than males (Torres and Drummond, 1999). Both sexes forage in the same areas (Zavalaga et al, 2007) and have similar diet composition (Ancona et al, 2012;Castillo-Guerrero and Mellink, 2011), but females can consume larger fishes than males (Castillo-Guerrero and Mellink, 2011;Zavalaga et al, 2007). Larger fish often have higher heavy metal concentration than smaller fish (Eisler, 1987).…”

“…Blue-footed Booby is a piscivorous seabird that, by plunge diving, prey mainly on sardines and anchovies in the first 3-4 m of water column (Zavalaga et al, 2007;Castillo-Guerrero and Mellink, 2011;Ancona et al, 2012). At the study site, with a multi-source Bayesian mixing model, the diet composition of adult birds varied throughout the breeding season, but the primary prey were Pacific anchovy (Cetengraulis mysticetus) and common halfbeak (Hyporhamphus unifasciatus), with a combined contribution of 50-60% (González-Medina, 2016).…”

Ecomorphology and foraging behaviour of Pacific boobies

“…Peruvian Boobies consume Peruvian Anchovy Engraulis ringens almost exclusively. In sympatry, larger bills in Blue‐footed Boobies may allow them to capture a broader range of prey as in their northern range (Castillo‐Guerrero & Mellink ). Both sexes of Peruvian Booby shifted to a smaller relative bill size in sympatry.…”

Regulation of breeding expenditure in the blue-footed booby, Sula nebouxii : an experimental approach

“…The durations and number of foraging trips and time spent at the nest were calculated from continuous monitoring of the control and experimental nests. Unless we recorded the exact moment that a bird departed from or returned to its nest, we used the hour midway between monitoring checks as an estimate (Castillo-Guerrero & Mellink, 2011;Guerra & Drummond, 1995). We considered any bird that was absent for more than 1 h to be on a foraging trip.…”