Animal-borne accelerometers allow body movement and behaviours to be recorded and identified. Quantifying these from free-living animals has many ecological applications, from identifying key behaviours in focal aspects of life history to estimating energy expenditure of locomotive patterns, all without direct observation. This is particularly valuable for species that are difficult to observe throughout their daily routines, such as those that utilise marine environments. Many seabirds navigate a three-dimensional landscape in unpredictable environmental conditions to find prey that are often patchy and widely distributed. Consequently, their foraging strategies, and utilisation of time and energy when foraging, are complex. Foraging effort and success determine the net energy gain by an organism and form an essential link between prey availability and reproductive success. Quantifying foraging energetics can be challenging, but aid in delivering sound conservation strategies in an era of intense environmental pressures and uncertainty.
By combining multifaceted data, principally accelerometers and GPS loggers, this thesis explored the at-sea movements of northern gannets, Morus bassanus, on a fine-scale individual basis. First, I examined associations between sexual dimorphism and sex differences. Within each sex, different facets of movements and behaviour were significantly related to body mass. However, the observed relationships were not consistent with the notion that sex differences were driven by sexual dimorphism. Secondly, I investigated the consistency in foraging behaviour and energy expenditure of individuals and the energy consequences of individual foraging site fidelity (IFSF). Birds were consistent in space use and energy expenditure but with varying degrees of repeatability among individuals and between sexes. The consequences of individuality were sex-specific, with greater IFSF associated with enhanced foraging success among females and elevated foraging effort among males. Third, I examined the effect of wind on fine-scale foraging behaviour and energy expenditure, finding that wind conditions strongly affected foraging behaviour, with contrasting effects of increasing wind speeds on females (lower take-off rates) and males (greater dive depths).
Overall, I demonstrate that not only do sexes and individuals differ in fine-scale behaviours and proxies of energy expenditure, but sex differences extend to the prevalence and consequences of individuality, and sexes respond differently to environmental conditions when foraging. This thesis highlights the need to consider sex differences and individuality when predicting the impacts of environmental change on populations of long-lived central-place foragers.
