Flexibility in otherwise consistent non-breeding movements of a long-distance migratory seabird, the long-tailed skua

Abstract

Quantifying within-and between-individual variation in animal migration strategies is a first step towards our understanding of the ability of migrants to adjust to changes in the environment. We studied consistency (or, conversely, flexibility) in movement patterns at large (>1000 km) to meso-scales (100−1000 km) during the non-breeding season of the long-tailed skua Stercorarius longicaudus, a long-distance migratory Arctic seabird, using light-based geolocation. We obtained 97 annual tracks of 38 individuals and quantified similarity between routes. Overall, tracks of the same individual were generally within about 200 to 300 km of their previous year's route, and more similar than tracks of different individuals. Some flexibility was observed during migration, but individuals were faithful to their staging areas in the North Atlantic and in the Benguela Current off Namibia and South Africa. Over the course of the winter, an increasing number of individuals started to deviate -up to 5200 km -from the previous year's route. Intriguingly, individuals could be highly consistent between 2 consecutive years and flexible between other years. Site-shifts in late winter seem to reflect responses to local conditions, but what promotes this larger flexibility remains unclear and requires further study. Our results show that individual long-tailed skuas are generally consistent in their itineraries, but can show considerable flexibility in some years. The flexibility in itineraries suggests that long-tailed skuas are able to adjust to environmental change, but the mechanisms leading to the observed within-and between-individual variation in movement patterns are still poorly understood.

Linking oceanographic conditions, migratory schedules and foraging behaviour during the non‐breeding season to reproductive performance in a long‐lived seabird

“…This is particularly interesting as long‐distant migratory species are often claimed to be limited in their individual plasticity in migration timing because of a rigid endogenous control of migration schedules and an inability to predict environmental conditions at their distant breeding grounds (Both & Visser, ; Knudsen et al., ). Yet, our study strongly suggests that long‐distant migrants have the abilities to adjust their migration schedules to winter environmental conditions (Cotton, ; van Bemmelen et al., ).…”

Causes and consequences of individual variability and specialization in foraging and migration strategies of seabirds

“…There is no effect of age per se on the nonbreeding strategy in the wandering albatross ) nor on the likelihood of an adult shifting its winter destination in the Cory's shearwater (Dias et al 2011). Indeed, Cory's shearwaters may switch back and forth between different regions (Dias et al 2013), and long-tailed skuas may switch between different routes in successive migrations (van Bemmelen et al 2017), indicating that these changes are not the result of accidental displacement by severe weather conditions. Hence, knowledge of the previous experience of the individual is key to understanding the navigation process, and the development of individual specialization in movements in general.…”

“…Few studies have examined site fidelity among rather than within breeding seasons (but see Wakefield et al 2015, Patrick & Weimerskirch 2017. During the nonbreeding season, individuals of most species tracked to date (15 of 20; see Table 4) showed a very high degree of foraging site fidelity at the regional level, with the notable exceptions of a small proportion of Cory's shearwaters, sooty shearwaters Ardenna grisea, long-tailed skuas Stercorarius longicaudus and 2 species of guillemots (Dias et al 2011, Hedd et al 2012, McFarlane Tranquilla et al 2014, van Bemmelen et al 2017.…”

“…In around half of the species tracked in multiple years, site fidelity of nonbreeding birds was much lower at the mesoscale than the regional level, and there was often little or no consistency in the use of staging areas and migration routes (Table 4). Black-browed albatrosses from South Georgia were consistent in the centroid of their terminal wintering area, but not in the use of staging sites (Phillips et al 2005); Scopoli's shearwaters showed significant repeatability in wintering region and some (but not all) aspects of migration schedule but not in the most westerly longitude reached during the return journey (Müller et al 2014); long-tailed skuas were generally faithful to staging and wintering area and to migration routes, but as the winter progressed, a small but increasing number of individuals began to deviate from their route in previous years (van Bemmelen et al 2017). Migration schedules (i.e.…”

A Migratory Divide Among Red-Necked Phalaropes in the Western Palearctic Reveals Contrasting Migration and Wintering Movement Strategies

“…For example, during the non-breeding season, migratory birds cover long distances to track spatio-temporal peaks in resource abundance and avoid unfavorable conditions over large spatial scales (Newton, 2010;Thorup et al, 2017). Nonbreeding movements may consist of a long-distance migration to wintering areas and movements within the wintering areas, which can cover long distances and-in some species-are carried out by only a portion of the individuals (Trierweiler et al, 2013;Koleček et al, 2018). Components of movement strategy, such as the number of staging sites, the distances between them, and the time spent at each staging site, are thought to be dictated by the availability and relative quality of habitat (Alerstam and Lindström, 1990;Gudmundsson et al, 1991).…”