Abstract
During breeding, animal behaviour is particularly sensitive to environmental and food resource availability. Additionally, factors such as sex, body condition, and offspring developmental stage can influence behaviour. Amongst seabirds, behaviour is generally predictably affected by local foraging conditions and has therefore been suggested as a potentially useful proxy to indicate prey state. However, besides prey availability and distribution, a range of other variables also influence seabird behavior, and these need to be accounted for to increase the signal-to-noise ratio when assessing specific characteristics of the environment based on behavioural attributes. The aim of this study was to use continuous, fine-scale time-activity budget data from a pelagic seabird (Cape gannet, Morus capensis) to determine the influence of intrinsic (sex and body condition) and extrinsic (offspring and time) variables on parent behaviour during breeding. Foraging trip duration and chick provisioning rates were clearly sex-specific and associated with chick developmental stage. Females made fewer, longer foraging trips and spent less time at the nest during chick provisioning. These sex-specific differences became increasingly apparent with chick development. Additionally, parents in better body condition spent longer periods at their nests and those which returned later in the day had longer overall nest attendance bouts. Using recent technological advances, this study provides new insights into the foraging behaviour of breeding seabirds, particularly during the post-guarding phase. The biparental strategy of chick provisioning revealed in this study appears to be an example where the costs of egg development to the female are balanced by paternal-dominated chick provisioning particularly as the chick nears fledging.
Highlights
Animals face a trade-off in time-allocation within their activity budgets which is dependent on their current state as well as external pressures [1, 2]
Nest attendance duration was best predicted by chick age, nest arrival time and adult body condition (Models N1 and N2; Table 1)
Using an extensive data set on foraging trip and nest attendance durations it was here clearly demonstrated that time-activity budgets in a chick-rearing seabird were sex-dependent and linked to chick development
Summary
Animals face a trade-off in time-allocation within their activity budgets which is dependent on their current state (e.g. breeding) as well as external pressures (e.g. predation risk) [1, 2]. While breeding, they are especially sensitive to environmental and resource availability [3]. Differing sexes have evolved traits which limit competition for similar resources while provisioning their offspring [8, 9]. In terms of offspring survival, accommodating these sex-specific behaviours is important for seabird conservation to ensure that the resource requirements of both parents are met [12, 13]
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