Field calibration of two survey methods to assess productivity of a ground-nesting wader, the Eurasian Curlew Numenius arquata

Abstract

ABSTRACT Capsule An alternative method for estimating the hatching and fledging success of wader nests from weekly survey visits yielded higher estimates of hatching success for Eurasian Curlews than an established method that involves visits at 2–3-weekly intervals, while requiring comparable survey effort. Aims To calibrate two methods of estimating the hatching success of Eurasian Curlews based on the alarm calling behaviour of adults: an established five-visit method versus a less frequently used territory-based method that involves more frequent monitoring of individual pairs. Methods We compared estimates of hatching success from the two methods using independent surveys on the same sites. We also estimated fledging success using the territory-based method and tested whether hatching success derived from this method predicted subsequent fledging success. We quantified the approximate field effort required to deliver both methods. Results Within-site comparisons revealed that estimated hatching success was consistently higher using the territory-based method than the five-visit method, probably due to more frequent visits for the former. For the territory-based method, hatching success of individual pairs was not a reliable predictor of their subsequent fledging success, suggesting that rates of breeding failure differ between nesting and chick-rearing periods. The territory-based and five-visit methods required comparable survey days to complete per site. Conclusion The territory-based method is a useful addition to the toolkit of methods for monitoring the productivity of Eurasian Curlews and other waders. It is a more complex method to deploy and requires the identification of individual pairs, but generates what are likely to be more reliable estimates of hatching success and an additional estimate of fledging success, compared to the five-visit method.