Wintering area and experience effects on spring migration strategies, timing and breeding success in Icelandic-nesting Common Scoters (Melanitta nigra)

Abstract

Earlier spring arrival of migratory birds to breeding sites and advanced breeding often bring enhanced reproductive success but demand good body-condition. When populations exhibit extensive winter distributions, the differing energetic costs associated with the quality and migration distance to each wintering area can have implications for individual breeding performance. Using light-level geolocator data from 30 female Common Scoters Melanitta nigra marked at their northeast Iceland breeding site, we explored the extent to which spring migration strategy, arrival and breeding times, and breeding success were related to minimum migration distances from wintering areas to breeding site in multiple years. Because many females produced multiple years of data, we further tested the degree to which individuals used their experience to arrive and breed earlier with increasing age. The females wintered c. 1000–4200 km from the breeding site, yet mostly (87% of 67 tracks) 1000–2000 km away. Increased distance was significantly related to earlier departure from wintering areas (c. 9 days/1000 km), longer stopover time en route and later arrival to breeding sites (c. 6 days/1000 km). Timing of breeding was unrelated to arrival time or migration distance, but significantly advanced with increasing female age (excluding one outlier). Increased migration costs associated with more distant wintering areas do not therefore seem to carry over to affect subsequent timing of breeding despite later arrival, potentially as a consequence of the higher quality of those wintering areas or adequate time after arrival to replenish depleted energy stores. However, further study is needed to elucidate potential effects of breeding time and/or migration distance on breeding success.