Sex-specific foraging over space and time in Cape gannets during chick rearing

Sex-specific foraging strategies have been documented in a range of seabird species, but the underlying mechanisms remain poorly understood. We aimed to assess spatial and temporal differences in the foraging behaviour of Cape gannets Morus capensis at Bird Island, Algoa Bay, South Africa. In total, 79 birds attending chicks younger than 50 d were fitted with GPS loggers over 2 consecutive years (2011/12, 2012/13). Furthermore, 95 additional birds were equipped with VHF tags to automatically record the temporal component of sex-specific foraging patterns over 3 consecutive years (2011/12, 2012/13, 2013/14). Using home range analysis and linear models, we found limited evidence for sex-specific differences over spatial dimensions. However, a slight extension in the foraging range of females during a year of lower prey availability was evident. This suggests a possible sex-specific response to prey limitation, which could reflect intraspecific competition or differences in nutritional requirements. Using a binomial generalized linear mixed effects model, applied to the VHF data, a clear pattern in temporal foraging behaviour emerged. In general, females were more likely to be on a foraging trip during the morning and midday hours, with the probability of males being on a foraging trip increasing towards late afternoon. These results provide insight into sex-specific behaviour in a monomorphic seabird, suggesting a marginal degree of spatial segregation, but provide the first support for sex-related temporal foraging segregation in gannets. Such separation could potentially reflect resource partitioning. In addition, synchronized foraging may also carry benefits in terms of chick provisioning and nest defence.