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- Data packageData from: Study "Northern Gannet Breeding Season GPS Data from Cape St. Mary's, NL, Canada: 2019 to 2022"(2023-05-01) d'Entremont, Kyle J.N.; Davoren, Gail K.; Montevecchi, William A.Seabirds are constrained by central-place foraging during breeding, when the energy obtained from prey must outweigh the costs of travel, search, capture and transport. The distribution and phenology of the cold-blooded marine fishes they exploit are heavily influenced by oceanic climate. Northern gannets, the largest breeding seabird in the North Atlantic, use a generalist foraging strategy, preying on a wide array of pelagic fishes. They employ different for- aging tactics for different prey types, with rapid, shallow V-shaped dives used for large, powerful prey such as mackerel, and U-shaped dives for smaller forage fishes like capelin. Here we assess intra- and inter-annual differences in foraging effort and influences of prey availability at the southernmost colony of the species at Cape St. Mary’s, Newfoundland, Canada. We compared for- aging trip characteristics (total and maximum distance, directness, duration and number of dives) of parental gannets during the breeding seasons of 2019 (n = 10) and 2020 (n = 7) using GPS/time- depth recorders. Individual gannets shifted away from using U-shaped dives in early chick- rearing to primarily V-shaped dives in late chick-rearing. Shifts were abrupt and occurred in mid-August in 2019 and 2020. Maximum and total foraging trip distance and duration were sig- nificantly greater during early chick-rearing in 2020 than in 2019. Kernel density 50% utilization distributions were larger and expanded further from the colony during early chick-rearing in 2020 (7297 ± 1419 km2; mean ± SE) than 2019 (2382 ±797 km2). Increased foraging effort during early chick-rearing in 2020 was likely due to decreased capelin availability, resulting from earlier spawning, and greater variation in the timing of spawning among sites, which may have been influenced by warmer waters.
- Data packageData from: Changes in behaviour drive inter‐annual variability in the at‐sea distribution of northern gannets(2017-08-01) Warwick-Evans, Victoria; Soanes, Louise M.; Gauvain, Roland D.; Atkinson, Phil W.; Arnould, John P.Y.; Green, Jon A.The at-sea distribution of seabirds primarily depends on the distance from their breeding colony, and the abundance, distribution and predictability of their prey, which are subject to strong spatial and temporal variation. Many seabirds have developed flexible foraging strategies to deal with this variation, such as increasing their foraging effort or switching to more predictable, less energy dense, prey, in poor conditions. These responses may vary both within and between individuals, and understanding this variability is vital to predict the population-level impacts of spatially explicit environmental disturbances, such as offshore windfarms. We conducted a multi-year tracking study in order to investigate the inter-annual variation in the foraging behaviour and location of a population of northern gannets breeding on Alderney in the English Channel. To do so, we investigated the link between individual-level behaviour and population-level behaviour. We found that a sample of gannets tracked in 2015 had longer trip durations, travelled further from the colony and had larger core foraging areas and home range areas than gannets tracked in previous years. This inter-annual variation may be associated with oceanographic conditions indexed by the North Atlantic Oscillation (NAO). Our findings suggest that this inter-annual variation was driven by individuals visiting larger areas in all of their trips rather than individuals diversifying to visit more, distinct areas. These findings suggest that, for gannets at least, if prey becomes less abundant or more widely distributed, more individuals may be required to forage further from the colony, thus increasing their likelihood of encountering pressures from spatially explicit anthropogenic disturbances.