PUB - Publikationen an der Universität Bielefeld

The Sociable Lapwing Vanellus gregarius is a critically endangered species, probably declining from 5000 pairs to 500 pairs in 11 years. Fieldwork was conducted at two sites in Kazakhstan, May-August 2004, to identify causes of the species' decline. In total, 58 nests and a minimum of 36 broods in 16 colonies were found: colonies consisted of 1-8 nests that were on average 154 m apart, with 2.1 km between colonies. Although classified as biparental, the total proportion of time both parents spent incubating was low (77 +/- 2% se, n = 13 nests). Daily survival rates (Mayfield method) were very low during incubation (0.943 +/- 0.009 se) but high during the chick stage (0.986 +/- 0.004 se); incubation and chick-stage durations were found to be 28.5 and 29 days, respectively, so that the overall probability of any breeding attempt fledging chicks was 0.124 (0.055-0.274 95% confidence interval). A breeding attempt that produced fledglings, fledged 2.2 +/- 0.2 se chicks (n = 26) on average. Observed productivity predicted the population decline over the last 11 years well (using the maximum number of nesting attempts per pair of 1.4 that could have occurred in this study, and assuming an adult and first-year survival rate of 0.74 and 0.60, respectively, based on the means for Northern Lapwing Vanellus vanellus and Golden Plover Pluvialis apricalia). Nest survival during incubation (controlling for colony effects) may have been longer for nests in predominantly Artemisia rather than grass habitat. Mean nest survival for a colony was higher in areas with more bare ground and more nest predators, suggesting that predators were relatively unimportant in nest (egg or chick) mortality, but was lower in areas with high numbers of cattle, suggesting that trampling was important (64% of known-cause nest failures, n = 11, were trampled). Nests were preferentially sited in areas of Artemisia, where there was greater dung abundance, and probably shorter vegetation, suggesting that highly grazed vegetation is important for nesting. Chicks preferentially selected areas with a lower percentage of bare ground and possibly taller vegetation, suggesting that more vegetated areas are important for chicks. The results suggest that low egg survival due to nesting in areas of high grazer density may be responsible for the Sociable Lapwing's decline. Although grazers may create suitable vegetation for initial nesting, if those grazers remain at high density as in anthropogenic systems then they may reduce nest survival, probably through trampling. Experimentally maintaining grazing early but reducing it later in the breeding season is the logical first step in managing the species to increase egg survival and so to increase productivity.