Nesting Success of Birds Breeding in Dutch Agricultural Grasslands

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Abstract
(1) Daily survival rates of nests with respect to predation are referred to as P-values, trampling survival rates are expressed as ''standardized trampling values'', estimated as daily survival rates at an exposure of one grazing animal ha-1. (2) P-values were lower during laying than during incubation. P-values in hidden-nesting species are higher than in open-nesting species. P-values are not constant, but are highest in the middle of the nesting season. P-values differ between regions and years, and are positively correlated with densities of voles, Microtus sp. In years following a collapse of vole populations, ground predators switch more to birds'' nests. (3) Standardized trampling values are independent of cattle densities and field size, hence the probability of surviving is a simple function of stock density and days exposure. (4) A renesting model is presented, to estimate nesting success per pair, taking renesting into account, based on P-values and trampling values. The model enables the testing of the effects of different management schemes on nesting success.

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