Autumn migration speed in Scandinavian BluethroatsLuscinia s. svecica

Open Access
Publisher Website
Google Scholar
Abstract
The average speed of autumn migration in Bluethroats was estimated using two different methods: calculations on ringing recoveries and comparisons of median arrival dates at several stop‐over sites. Estimates revealed by these two methods were similar, indicating that temporal data from stop‐over sites can reliably monitor the timing of migration. Females arrived before males at stop‐over sites in Scandinavia (in juveniles mean difference 3 days: in adults 0.9 days), but estimates of migration speed were similar between the sexes. The migration speed in juveniles was estimated to be 30–40 km per day for migration in Sweden, and to be 40–65 km per day for migration to Finland. Adult birds migrated significantly faster than juveniles during the first part of the autumn migration (100–110 km per day). It is suggested that the age difference in migration speed within Scandinavia may be due to differences in fat accumulation and stop‐over times between the age classes. Possibly, simultaneous migration and completion of the post‐juvenile moult also has a negative effect on the migration speed in juveniles. The migration speed in juveniles increased as the autumn progressed, approaching average values of 100 km per day for migration to southwestern Asia. There are no data available that can explain this situation, although factors such as the rate of fat accumulation at different stop‐over sites along the migration route, experience and selection are discussed.