Diel at‐sea activity of two species of great albatrosses: the ontogeny of foraging and movement behaviour

Abstract

The first year of life is a period of high mortality in animals. Reduced foraging capacities of naive individuals might be the primary cause of their mortality. These capacities are supposed to be progressively acquired during the first months of life. In this study, we investigate the ontogeny of flight capacities, by day and night, of first‐year individuals, and compare it with adults from two closely related species of great albatrosses: Amsterdam Diomedea amsterdamensis and wandering Diomedea exulans albatrosses which forage in different environmental conditions. We used 71 tracks of 71 juvenile birds and 141 of 116 incubating adults to compare both age categories. In order to explore the effect of moon light on night activity, we elaborated a new formula which improves the precision of the proxy of moon illumination. By day, we found that juveniles of both species reach some adult foraging capacities in less than two months. By night, albatrosses have reduced activity increasing during the first weeks at sea for juveniles and changing in accordance with moon illumination for both juveniles and adults. A peak of flight activity at dawn and dusk was apparent for both species. Interspecific comparison underlined that Amsterdam albatrosses were more active than wandering albatrosses, suggesting a difference in food and foraging strategy. Overall, we highlighted how life history traits, environmental conditions and time of the day affect the foraging activity of two related species of seabirds.

The challenges of independence: ontogeny of at-sea behaviour in a long-lived seabird

“…The lower performance of juveniles we found is consistent with studies on wandering albatrosses and Amsterdam albatrosses (Riotte-Lambert and Weimerskirch 2013; de Grissac et al 2017;Pajot et al 2021) during the first weeks at sea, which found that shortly after fledging juvenile albatrosses employ similar foraging strategies as adults. Additional skills need to be acquired during the immature period before the efficiency of these behaviors matches that of adults.…”

“…Though the diet and foraging strategy of Amsterdam albatross remains poorly known, it is presumed to have very similar foraging behaviour compared to that of the Wandering albatross, although subtle differences can appear (Pajot et al 2021). Although Amsterdam albatross is 5-8% smaller and 25% lighter than wandering albatross, the two species have a very close anatomy and similar use of the wind.…”

“…In this oceanic area, the southern subtropical front (SSTF) delimits the warmer subtropical from the colder sub-Antarctic waters (Belkin & Gordon 1996). Though the diet and foraging strategy of Amsterdam albatross remains poorly known, it is presumed to have very similar foraging behaviour compared to that of the wandering albatross, although subtle differences can appear (Pajot et al 2021; see Supplementary). Like other large albatross species ( Diomedea spp.…”

“…We also predict sharp changes in activity following fledging of juveniles from the colony followed by more progressive changes. Based on results found on fledglings wandering albatross (Riotte-Lambert and Weimerskirch 2013; Pajot et al 2021) showing that juveniles reached some adult foraging capacities in less than two months, we predicted that important changes should be detected in activity parameters early after the juvenile left the colony (within few first months). Overall, juveniles should show higher foraging effort compared to other life-stages (i.e.…”

Ontogeny of movement patterns and habitat selection in juvenile albatrosses

“…Individual steps were then assigned to daylight or darkness using function crepuscule in package maptools to determine the timing of civil twilight, when the sun is 6 degrees below the horizon (Bivand and Lewis‐Koh 2017). Step lengths of birds were much shorter during darkness than daylight (9.1 ± 12.1 versus 23.7 ± 18.1 km h −1 ) suggesting that juveniles rarely travel or search for prey during darkness (Supporting information and in line with de Grissac et al 2017, Pajot et al 2021); hence steps occurring during the night were excluded from the i SSA. A further two birds were removed from the final test dataset as observations were too few (< 26) to account for within‐individual temporal autocorrelation.…”