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.On a de plus en plus de preuves que les recensements d'échassiers nicheurs ont souvent largement sous-estimé les densités dans l'Arctique et dans d'autres régions. Ces preuves comprennent le fait que l'on recense beaucoup plus de bécasseaux maubèches, Calidris canatus, dans les aires d'hivernage du paléarctique occidental et d'Afrique que l'on ne peut en compter sur les lieux de reproduction dans l'Arctique. Les principales raisons de cette sous-estimation sur les lieux de reproduction sont que bien des espèces ont un comportement peu visible pendant l'incubation, c'est-à-dire au moment où sont effectués la plupart des recensements, et que ceux faits plus tard, durant la période d'élevage des poussins, ne comptent que les tentatives de reproduction réussies. Les relevés effectués au cours de quatre saisons à Zackenberg, dans la région centrale du nord-est du Groenland, suggèrent que, dans l'Arctique, les meilleures données sur la densité de population sont obtenues en notant les paires et les individus territoriaux durant la formation des paires, l'établissement du territoire et la période de ponte, c'est-à-dire quand tous les oiseaux sont présents et le plus facile à compter. Les estimations révisées des populations estivales pour les échassiers néarctiques hivernant dans l'Ancien Monde sont de 20 à 200 p. cent plus élevées que les estimations précédentes

Arctic Biodiversity Assessment - Author Principles and Guidelines March 2009

Arctic Council´s Conservation of Arctic Flora and Fauna Working Group (CAFF): Arctic Biodiversity Assessment - Author Principles and Guidelines March 200

A single-year comparison of two methods of censusing breeding Red Knot and Sanderling in High Arctic Greenland

A uniquely intense field effort at Zackenberg, NE Greenland, in June–July 2003 made it possible, for the first time, to compare two methods of measuring breeding densities of two notoriously difficult-to-census High Arctic breeding shorebirds (Red Knot Calidris canutus and Sanderling Calidris alba): (1) mapping of displays and other activities of birds in a rapid assessment early in the season, and (2) systematic ‘roping’ of potential breeding areas to disturb and then find incubating birds on, or very close to, their nests. The latter method is particularly relevant to species that rely on crypsis to avoid nest detection. During 16 and 19 June an experienced observer, in a standardized way, mapped all visual observations of Red Knot and Sanderling over a 4.0 km2 study area, which consisted mainly of low-angle mountain slopes between altitudes of 100 and 400 m. The observations were interpreted to represent 8–9 ‘pairs’ of Red Knot and 13–17 ‘pairs’ of Sanderling. Observations nearby allowed for a few additional pairs of Red Knot. Between 17 June and 5 July a team of five observers systematically roped the same study area and found two Red Knot nests and 15 Sanderling nests. Most of the study area remained under daily scrutiny until 19 July, and during these visits we encountered two more families of Red Knots and seven more Sanderling families. Thus, the roping effort yielded a few more Sanderling ‘pairs’ than expected from the early-season survey, but fewer Red Knot. This may imply that either: (1) the early-season rapid assessment particularly overestimated the knot population, and/or (2) relative to Sanderlings, knot nests were heavily depredated before roping, and/or (3) incubating birds escaped notice during roping, and/or (4) some of the local Red Knots may not have started a breeding attempt at all. Further work with radio-tagged individuals is necessary to establish whether we need to invoke non-breeding as a cause of the discrepancy

Sex-ratio and body size of sandpiper chicks at Zackenberg, north-east Greenland in 2003

There is growing evidence that female birds may adaptively bias the sex ratio of their young as a function of environmental conditions. Data on brood sex ratio in shorebirds are scarce, however. In this study we report the brood sex ratios and morphometrics of Arctic sandpipers. Sex was determined in 13–64 chicks of Sanderling Calidris alba, Red Knot Calidris canutus islandica, Dunlin Calidris alpina arctica, and Ruddy Turnstone Arenaria interpres in NE Greenland during the 2003 breeding season. Brood sex ratios were biased significantly towards males in Dunlin and Ruddy Turnstone, but in Dunlin this bias disappeared in chicks older than two days. There was a non-significant bias towards females in Sanderling and Red Knot. Only for bill length in Dunlin hatchlings, there were significant differences between males and females. Surprisingly, in contrast to their parents, male chicks had longer bills than female chicks

Interaction webs in arctic ecosystem : Determinants of arctic change?

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