Seasonal contrasts in individual consistency of oriental honey buzzards' migration

High individual repeatability of the migratory behaviour of a long-distance migratory seabird

BACKGROUND

Understanding the evolution of migration requires knowledge of the patterns, sources, and consequences of variation in migratory behaviour, a need exacerbated by the fact that many migratory species show rapid population declines and require knowledge-based conservation measures. We therefore need detailed knowledge on the spatial and temporal distribution of individuals across their annual cycle, and quantify how the spatial and temporal components of migratory behaviour vary within and among individuals.

METHODS

We tracked 138 migratory journeys undertaken by 64 adult common terns (Sterna hirundo) from a breeding colony in northwest Germany to identify the annual spatiotemporal distribution of these birds and to evaluate the individual repeatability of eleven traits describing their migratory behaviour.

RESULTS

Birds left the breeding colony early September, then moved south along the East Atlantic Flyway. Wintering areas were reached mid-September and located at the west and south coasts of West Africa as well as the coasts of Namibia and South Africa. Birds left their wintering areas late March and reached the breeding colony mid-April. The timing, total duration and total distance of migration, as well as the location of individual wintering areas, were moderately to highly repeatable within individuals (repeatability indexes: 0.36-0.75, 0.65-0.66, 0.93-0.94, and 0.98-1.00, respectively), and repeatability estimates were not strongly affected by population-level inter-annual variation in migratory behaviour.

CONCLUSIONS

We found large between-individual variation in common tern annual spatiotemporal distribution and strong individual repeatability of several aspects of their migratory behaviour.

The State of Migratory Landbirds in the East Asian Flyway: Distributions, Threats, and Conservation Needs

With nearly 400 migratory landbird species, the East Asian Flyway is the most diverse of the world’s flyways. This diversity is a consequence of the varied ecological niches provided by biomes ranging from broadleaf forests to arctic tundra and accentuated by complex biogeographic processes. The distribution and migration ecology of East Asian landbirds is still inadequately known, but a recent explosion in the number of studies tracking the migration of raptors, cuckoos, kingfishers and passerines has greatly increased our knowledge about the stopover and wintering ecology of many species, and the migratory routes that link northeast Eurasia and the Asian tropics. Yet the East Asian Flyway also supports the highest number of threatened species among flyways. Strong declines have been detected in buntings (Emberizidae) and other long-distance migrants. While the conservation of migratory landbirds in this region has largely focused on unsustainable hunting, there are other threats, such as habitat loss and increased agro-chemical use driven directly by land cover change and climate-related processes. Important knowledge gaps to be addressed include (1) threats affecting species in different parts of their annual cycle, (2) range-wide population trends, (3) ecological requirements and habitat use during the non-breeding season, and (4) the conservation status of critical wintering sites (including understudied farming landscapes, such as rice fields) and migration bottlenecks along the flyway.

Genetic Structure in Japanese and Thai Populations of the Japanese Sparrowhawk Accipiter gularis

The Japanese sparrowhawk Accipiter gularis is a small raptor that breeds in Northeast Asia. The species consists of the widespread and mostly migratory subspecies A. g. gularis that is common in East Asia, including Japan, and the resident and endangered subspecies A. g. iwasakii which inhabits the Ryukyu and Yaeyama Islands in Okinawa, southern Japan. Given the minimal knowledge about the migration of the species, in this study we sought to compare the genetic variation of the populations breeding in Japan with those migrating through Southeast Asia. We sequenced 761 bp of mitochondrial DNA Control Region from each of 21 A. gularis collected during the breeding season in Japan and from 20 individuals intercepted on migration in Thailand. We detected 26 haplotypes among the 41 individuals which differed significantly between Japan and Thailand. Migrants in Thailand were presumed to have originated from a wide area in Eastern Eurasia. The phylogenetic and network analyses demonstrated that the haplotypes of all A. g. gularis detected in Japan were genetically close. Moreover, the Okinawa haplotypes of A. g. iwasakii were clustered with moderate genetic variation. The information presented here can be used towards implementing future conservation actions.

Seasonal contrasts in individual consistency of oriental honey buzzards' migration

Individual consistency in migration can shine light on the mechanisms of migration. Most studies have reported that birds are more consistent in the timing than in the routes or stopover sites during migration, but some specialist species showed the opposite patterns, being more consistent in spatial than temporal aspects of migration. One possible explanation for this contrast is that specialists rely on particular food or habitat resources, which restrict the migratory routes they can take, leading to high spatial consistency. If this is the case, the effect of specialist foraging should become apparent only when birds forage, instead of fasting and flying continuously. To test this effect, we analysed individual consistency in migration of the oriental honey buzzard ( Pernis ptilorhynchus), a specialist raptor that feeds on honeybees and wasps, using a long-term tracking dataset. As honey buzzards make extended stopovers during which they forage in spring but not in autumn, the spatial consistency should be higher in spring than in autumn. Honey buzzards were highly consistent in both their migratory routes and stopover sites in Southeast Asia, but only during spring migration. Our results highlight an important link between species' migratory consistency and foraging ecology.