Autumn Phenology and morphometrics in the Garden Warbler Sylvia borin at the Ottenby Bird Observatory, Sweden

Trapping and ringing near ecological barriers can provide useful information about the migration strategies of bird species. In this paper we analyzed ringing data of the Garden Warbler, collected within the period of 19502008 at the Ottenby Bird Observatory, south-eastern Sweden, and describe patterns inmigration phenology,morphometrics and fuel load.Atotal of 4,351 individuals aged as either adults or juvenileswere ringed during the period (yearly averages 7.3 adults and 83.1 juveniles) in addition to 1,514 birds of unknown age. Both age-specific and combined yearly totals did not significantly vary over the years.Median passage dates were 24 August, 30 August and 2 September for adults, juveniles and birds of unknown age, respectively.Median passage did not change significantly over the years.Among adults, larger individuals passed the observatory earlier than smaller individuals. The average fuel load was estimated at 24.3% of Lean Body Mass (LBM), and late-migrating individuals had higher fuel deposits than earlymigrants.Maximum fuel load was estimated at 82.5% of LBM; such an individual may be capable of a direct flight from Ottenby region to the Mediterranean area.