Resumen:
Coastal marshes play a relevant role as stopover and fuelling sites for birds during migration period. The importance of tide in such ecosystems is well studied for aquatic species such as waders, but its impact on the stopover behavior of land birds that also depend on these sites is still unknown. Bluethroats Luscinia svecica are small-sized passerines that feed on the ground and low vegetation and, therefore, experience continuous changes of habitat availability due to the tide regimens. The aim of this study was to analyse the habitat use and to test the impact of tide on home range size of Bluethroats stopping over at coastal marshes. For that, we used data on radio-tagged birds at a tidal marsh in Northern Iberia. Bluethroats were radiotracked from the 20th of August to the 20th of September. Individuals were surveyed from 3 to 17 days, and birds with lower body mass at the day of capture stayed for longer period. Mean home range size was 2.0 ha (SE = 0.2), and the main habitats occupied were reedbeds (ca. 30% of a home range area) together with tidal flats with both free- and low-halophytic vegetation (30%). Reedbeds were situated at a higher altitude over the sea level than open waters, mudflats and low halophytic vegetation. Home ranges tended to be larger in birds found to occupy zones close to the sea level, thus with a longer tide-mediated flooding period, suggesting a negative effect of tide on home range size, and/or that Bluethroats staying at lower altitude did not find as much food as at higher altitude, so they were forced to move over larger surfaces.
