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

Growth and survival of chicks and movements of broods were studied in Curle w Sandpipers in N.E. Taimyr, Siberia, in 1991. Breeding was synchronised, 7 3% of 30 clutches hatching during 10-15 July. Nests were distributed clumpe d 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 fir st week of life. Here, they often formed aggregations of 2-6 broods with fe males cooperating in predator defence. In 1991 (a lemming peak year), both clutch and chick survival were high, and breeding productivity was c. 2 fle dglings 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 r ate was reduced during cold weather, as was the availability of surface-act ive arthropods which form the main food source for chicks. Effects of weath er on chick survival and breeding productivity were examined by correlating data on annual variation in the proportion of juveniles among wintering bi rds in South Africa with 18 years of summer weather records from the core o f the Taimyr breeding area. After allowing for an effect of three-yearly cy clic variation in lemming abundance on predation of eggs and young by arcti c foxes and skuas, breeding productivity was positively correlated with mea n temperature in Taimyr during 11-20 July, the period when most young chick s are present in the tundra. Weather thus seems to have effects on chick su rvival both widespread and large enough to be detected in the wintering are as, and the combination of (inferred) predation pressure and weather condit ions during the hedging period explains a large part of the variation in br eeding productivity found in this species. We found no correlations between productivity and weather during the pre-laying period, in contrast to seve ral studies on arctic-breeding geese.