Nest box selection and reproduction of European Rollers in Central Italy: a 7-year study

Background: Changes and increased mechanisation of agricultural practices have influenced the biodiversity composition of farmland habitats and caused a decline of bird communities in many European countries. The removal of shrubs and large trees rich in natural cavities, has also led to a drastic decrease in nest site availability for cavity-nesting bird species. Nest-boxes are a common conservation tool used to improve nest-site availability, and have helped to reverse declines in many endangered bird populations. Nonetheless to maximize the results of such interventions it is crucial to know where nest-boxes should be sited. The objective of this study was to investigate the effectiveness of the nest-box program for the European Roller (Coracias garrulus) population of Lazio region (Central Italy). More specifically, we focused on what landscape features were preferred (or avoided) in the process of nest box selection and how they influenced population’s breeding parameters. Particular attention was paid to identifying potential limitations and to provide management recommendations for future interventions. Methods: Using data from 70 nest boxes sited on power lines monitored over a 7-year period (representing 140 breeding attempts), we developed probability functions to evaluate if nest box location, in terms of distance from habitat resources and habitat composition and structure, had an effect on nest box occupancy and on the main reproductive parameters. Results: Nest boxes were more likely to be occupied if they were located near arable fields and in areas characterized by a higher amount of incoming solar radiation. Higher fledging success was associated with fallow fields and with a moderate/low habitat structural complexity. Higher breeding success was associated with solar radiation and with greater distance from urban areas. Conclusions: Our results highlight the importance of specific habitat variables in influencing nest occupancy, and show which drivers primarily affect species’ reproduction and persistence over time. Siting nest boxes in habitats where occupancy rate and fledging success is higher, such as in arable and fallow fields and on south-facing slopes where solar radiation is maximised, may help to extend the suitable habitat for rollers and facilitate its local expansion.

Breeding phase and outcome determine space use in European rollers Coracias garrulus prior to migration

The breeding period is a demanding and time-constrained phase for migratory bird species.Breeding outcome and duration can interact with the extent and duration of post-breeding movements,resulting in individual differences in space use ultimately influencing later stages of the annual cycle.We present space-use and home range estimates during the breeding season for 21 European rollers Coracias garrulus tracked between 2018 and 2022,in Italy and Croatia.Using high-resolution spatial GPS data coupled with regular nest-box monitoring,we analyzed dif-ferences in space use during the incubation/nestling period versus post-breeding period prior to migration,accounting for the breeding outcome(successful vs.failure).We found that adult movements were strongly reduced during the first phase,whereas increased in the post-breeding phase,especially for failed breeders.Successful breeders remained in the surroundings of the nest site,whereas unsuccessful ones tended to abandon the nest and visit distant areas(up to 500 km)for long periods(60.5±6.2 days).Breeding outcome did not influence the departure date of autumn migration,suggesting that failed breeders used this period for exploratory movements but not for advancing the onset of migra-tion.Such exploratory movements may be functional to prospect and inform settlement decisions in failed breeders in search of new breeding opportunities and may be particularly important in migratory species,which generally have a limited period to gather information prior to autumn migration.The study demonstrates the need to investigate seasonal movements in different populations and the potential importance of pros-pectingpost-breeding movements for long-distance migratory species.