Regulation of stopover duration in the European Robin Erithacus rubecula

Analysis of factors that influence stopover departure decisions in migrating birds is an important step in understanding their movements. We studied body condition, refuelling efficiency and weather during arrival and subsequent departure of migrant European Robins Erithacus rubecula at a stopover site on the Courish Spit (Eastern Baltic) to explain why some birds continued migration on the night following arrival (‘transients’) while others stopped over for a more prolonged period (‘non-transients’). Analysis of 125 uniquely recaptured birds showed that long stopovers could not explained by adverse weather during the night following arrival. Comparison of arrival fuel loads in ‘transient’ and ‘non-transient’ individuals revealed no clear differences and most birds were able to gain mass. Only the combined consideration of both energetic and weather parameters showed that departure decisions depended on simultaneous action of nearly all factors. In ‘non-transient’ birds, the exact stopover duration is governed by a combination of achieved fuel deposition rate/fuel stores and the prevailing weather pattern. In spring, European Robins selected optimal wind condition to start a new flight bout while in autumn they departed under moderately unfavorable winds.