Sex-, year-, and colony-specific at-sea movements of Australasian gannets Morus serrator during the non-breeding period

Animals typically reproduce at the time of year when environmental conditions and food availability are optimal. These may decline after the reproductive period; consequently, individuals that are no longer constrained by central-place foraging for offspring provisioning may leave the breeding area. For marine species, obtaining direct information about at-sea movements and distribution during the non-breeding period can be challenging, causing a lack of knowledge for this important part of the annual cycle. In the face of a changing environment, obtaining such information is essential for predicting potential consequences on population trajectories. Here we used light level geolocators to investigate the non-breeding movements, and intrinsic factors influencing them, of Australasian gannets Morus serrator from 2 colonies in northern Bass Strait, south-eastern Australia, in 2 consecutive years. Tracking data revealed that, while some gannets remained within their breeding season foraging range during the non-breeding period (n = 15), many individuals travelled widely along the southern Australia continental shelf, from Cape Leeuwin in the west to the eastern seaboard of the continent (n = 84). The continental shelf areas of western Tasmania and Bass Strait were the most frequented. Most individuals exhibited nomadic behaviour, with no overall pattern or synchronicity in their movements. Data suggested differences between sexes and years in the at-sea movements of individuals, potentially due to differences in foraging strategies and environmental conditions, respectively. However, the collection of long-term data and higher-resolution tracking data is required to investigate potential consequences on the species in a changing environment.