Growth, behaviour of broods and weather-related variation in breeding productivity of Curlew Sandpipers <i>Calidris ferruginea</i>

Growth and survival of chicks and movements of broods were studied in Curlew Sandpipers in N.E. Taimyr, Siberia, in 1991. Breeding was synchronised, 73% of 30 clutches hatching during 10-15 July. Nests were distributed clumped in dry frost-heaved tundra. Broods were tended by females only and moved from the nest sites to low-lying wet areas up to 2.4 km away during the first week of life. Here, they often formed aggregations of 2-6 broods with females cooperating in predator defence. In 1991 (a lemming peak year), both clutch and chick survival were high, and breeding productivity was c. 2 fledglings per female. Chicks fledged in 14-16 days, and body mass growth was best described by a logistic curve. The growth rate constant K-L was 0.314, which is high compared to similar-sized waders studied elsewhere. Growth rate was reduced during cold weather, as was the availability of surface-active arthropods which form the main food source for chicks. Effects of weather on chick survival and breeding productivity were examined by correlating data on annual variation in the proportion of juveniles among wintering birds in South Africa with 18 years of summer weather records from the core of the Taimyr breeding area. After allowing for an effect of three-yearly cyclic variation in lemming abundance on predation of eggs and young by arctic foxes and skuas, breeding productivity was positively correlated with mean temperature in Taimyr during 11-20 July, the period when most young chicks are present in the tundra. Weather thus seems to have effects on chick survival both widespread and large enough to be detected in the wintering areas, and the combination of (inferred) predation pressure and weather conditions during the hedging period explains a large part of the variation in breeding productivity found in this species. We found no correlations between productivity and weather during the pre-laying period, in contrast to several studies on arctic-breeding geese.