The global importance of grasslands underlined by the combination of multiple telemetry tracking techniques of a trans-equatorial loop migrant bird, the European roller (Coracias garrulus).

Abstract

Migrant birds encounter different conditions and threats across seasons, so their population dynamics are affected by the events in both breeding and nonbreeding seasons. The decline of long-distance migrant, grassland specialist birds underlines the necessity of integrating the full annual cycle perspective in conservation research. The European roller (Coracias garrulus), as a long-distance migratory grassland bird, is an excellent model species for exploring the environmental parameters that may contribute to the vulnerability of birds with similar requirements through the full annual cycle. Here, we aim to identify the migration strategies and phenology to locate the stopover sites and wintering grounds and to describe the home-range size and habitat composition during the breeding season and the non-breeding season. We studied the breeding population of the Carpathian Basin between 2015 and 2021. We used GPS-UFH loggers to investigate movements during the breeding season and PTT tags and geolocators for tracking during the non-breeding season. For the habitat use analysis, we employed European and global land cover databases. We found that home-range size changed over the breeding season, the availability of grasslands affected the size of the home-range and the core area harboured the largest proportion of grasslands. During the non-breeding period, 108 stopover sites were identified. During autumn, rollers used more stopovers compared to the spring migration. Although rollers migrate on broad fronts during autumn migration, two main stopover regions were identified: a sub-Saharan and a subequatorial. Rollers spent significantly more time at the stopover sites in the sub-Saharan region than in the subequatorial region or during the spring migration. We found multiple migration pathways and a wide east-west spread over the wintering grounds in the southern savanna region. Rollers mainly used grassland habitats, especially on the wintering sites, where rollers spend the longest time during the non-breeding period. Here, we firstly provided a detailed overview of the spatial and temporal scale of rollers’ habitat use through the full annual cycle, proving the global importance of grasslands in the conservation of long-distance migratory birds. In our view such detailed knowledge is crucial for developing conservation strategies applicable to the whole Afro-Palearctic flyway system.