Timing of migration of the Curlew Sandpiper {Calidris ferruginea) through Poland in relation to Arctic breeding conditions

Abstract

Recent shifts in the timing of migration and breeding have been attributed to climate variation in some migratory birds. However, the divergent patterns in the timing of autumn migration among different bird species suggest a significant role of factors other than climate. Using data of constant-effort catches, determinants for the annual variation in the timing of migration were investigated in the Curlew Sandpiper Calidris ferruginea in Poland. Variation in the timing for adult and juvenile Curlew Sandpipers was influenced by breeding success, which was in turn connected to predation pressure, and June and July temperatures on the species' breeding grounds in the Arctic region. Median date of passage of adults was significantly later in good than in poor breeding years. The migration of adults was earlier by 2.3 days for every 1°C increase in average June temperature in the Arctic breeding grounds. Median migration date of juveniles was positively correlated with predation and negatively with June temperature in the Arctic breeding grounds. Median migration date of adults advanced by a factor of-0.59 days/year, which translates into 10 days from 1984-2000. These results suggest that conditions on breeding grounds can affect the timing of subsequent events within the annual cycle. Circumstantial evidence also suggests that climate change may have increased the predation on young Curlew Sandpipers, increasing the frequency of poor breeding years and modifying the timing of autumn migration in these waders.