Data associated to: A bioenergetics approach to understanding sex differences in the foraging behaviour of a sexually monomorphic species

Many animals show sexually divergent foraging behaviours reflecting different physiological constraints or energetic needs. We used a bioenergetics approach to examine sex differences in foraging behaviour of the sexually monomorphic northern gannet. We used the relationship between dynamic body acceleration and energy expenditure to investigate energetic cost of prey capture attempts (plunge dives). Fourteen gannets were tracked using GPS, TDR, and accelerometers. All plunge dives in a foraging trip represented <4% of total energy expenditure, with no significant sex differences in expenditure. Despite females undertaking significantly more dives than males, the low energetic cost resulted in no sex differences in overall energy expenditure across a foraging trip. Bayesian stable isotope mixing models based on blood samples highlighted sex differences in diet, however, calorific intake from successful prey capture was estimated to be similar between sexes. Females experienced 9.6% higher energy demands, due to unequal chick provisioning. Estimates show a minimum of 21% of dives have to be successful for females to meet their daily energy requirements, and 29% for males. Our analyses suggest northern gannets show sex differences in foraging behaviour primarily related to dive rate and success rather than the energetic cost of foraging or energetic content of prey.