Estimating the abundance and hatching success of breeding Curlew Numenius arquata using survey data

Counts of individual Curlew and estimates of breeding pairs from 'field-by- field' surveys were highly correlated with the numbers of nesting pairs, ns determined by intensive studies on 27 sites located on four grassland-domi nated study areas. The mean count of individual Curlew over three standard survey visits to each site was used to estimate numbers of nesting pairs. T his estimate exceeded the number of nesting pairs on all study areas (as as sessed by intensive studies) by 12% but was move accurate than the maximum number of pairs estimated from the three survey visits on each site (the pr evious convention for estimating breeding pairs). Estimates of the number o f pairs hatching chicks were assessed by recording alarm-calling Curlew dur ing late survey visits. The maximum number of alarm-calling pairs was used to estimate the number of pairs hatching chicks, overestimating this by 54% . Three of the study sites were adjacent to extensive moorland which produc ed overestimates during surveys because moorland nesting birds fed and Zed broods onto these sites. Omitting these sites from consideration reduced th e degree of overestimation to 1% for the number of pairs and 7% for the num ber of pairs hatching chicks.