Alternative foraging strategies in the white stork Ciconia ciconia: The effect of mowing meadows

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The intensification of farm management practices on grasslands has reduced the abundance of many species of animals. Mowing, a procedure essential to the continuing existence of farmland meadows, inevitably causes mortality among the animals inhabiting them, especially invertebrates, and exposes sites where white storks Ciconia ciconia can forage conveniently and more efficiently. We studied the foraging activities of storks on meadows being mown and compared these with the birds’ foraging patterns on unmown meadows and meadows cleared of hay in the extensively managed farming landscape of east-central Poland. Foraging success was deemed to be the capture of a prey item as manifested by the stork raising its head and swallowing prey item. The storks’ foraging success on meadows being mown was roughly the same as on unmown meadows but was significantly lower than on those cleared of hay. The number of steps taken by storks – a measure of the energy they expended on foraging – was far higher on meadows being mown than on unmown ones. Even so, on meadows being mown, storks caught proportionately more vertebrates (voles) (5.2% of all prey items) than on cleared meadows (1.4%) and unmown meadows (0.2%). The fact that vertebrates are considerably energy-richer than invertebrates was probably the main reason why storks were attracted to forage on meadows being mown, even though their foraging efficiency was not particularly high – an aspect emphasised in the literature. The sequential (asynchronous) mowing of the highly fragmented, semi-natural meadows in this part of Poland coincides with the time when storks are feeding their young. This is probably a key aspect governing the high density of this species.