Wader Population Censuses in the Arctic: Getting the Timing Right

There is increasing evidence that breeding wader censuses often have significantly underestimated densities in the Arctic and other areas. This evidence includes the recording of many more red knots Calidris canutus in the West Palearctic and African wintering areas than can be accounted for on the Arctic breeding grounds. The main causes of underestimated breeding numbers are that many species behave very inconspicuously during incubation, when most censuses have been performed, and that censuses taken later, during the chick-rearing period, record only successful breeding attempts. Records of four seasons at Zackenberg in central Northeast Greenland suggest that in the Arctic, the best population density data are obtained by mapping pairs and territorial individuals during the pair formation, territory establishment, and egg-laying periods, that is, when all birds are present and easiest to record. Revised summer population estimates for Old World wintering Nearctic waders are 20–200% higher than previous estimates.