Stopover ecology of autumn-migrating Bluethroats (Luscinia svecica) in a highly anthropogenic river basin

摘要

Wetlands are highly productive habitats used by many avian species as stopover sites during their migrations. However, these habitats are highly threatened by anthropogenic activities, such as land-use changes, the introduction of exotic species, and global warming. Further understanding on the spatiotemporal use of wetlands and their surrounding areas by migrating birds is essential to predict how these changes might affect avian en route ecology. We selected a habitat-generalist passerine, the Bluethroat Luscinia svecica, as model of how migratory birds exploit a highly anthropogenic river basin in southwestern France (i.e. Barthes de la Nive) during autumn migration. We captured and radiotracked 29 young Bluethroats in this region to shed light on different aspects of their stopover ecology and behavior such as stopover duration, habitat selection, and home-range size. We also characterized Bluethroat diet and arthropod availability in different habitats. Bluethroats positively selected pure or mixed reed beds (associated with sedge), hydrophilous tall grasslands, and corn crops. Birds staying more than one day, 8.4 days on average, used preferably corn crops. Home-range sizes were on average 5.8 ha (fixed kernels K95) and high-occupancy area (K50) was 1.36 ha with large individual variation. Bluethroats stopping over with low fuel loads tended to have larger home ranges and used preferentially corn crops, wet, or mesotrophic grasslands and rural paths. Reed beds were typically used as roosting habitat for the majority of birds, being on average 397 m apart from their daytime core areas. Short-staying birds tended to show higher fuel loads and restricted their activities to a smaller home range (1 ha) in pure and mixed reed beds. The diet of Bluethroats was dominated by ants, spiders, and beetles that were particularly abundant in corn crops. The use of corn crops by autumn-migrating Bluethroats in our study site seems to be a reasonable solution in a highly altered environment. Reducing the use of insecticides in these crops and delaying the harvesting time after mid-October are two supplemental measures that, together with a good management of the remaining wetland patches, could greatly favor Bluethroats and other migratory species in this region.