Survival and behaviour of Corncrake Crex crex chicks during the mowing of agricultural grassland

The behavior of Corncrakes during mechanized mowing of hay and silage was investigated by tracking radio-tagged females with broods and observing chicks escaping from meadows or being killed by the mower. Except in the case of very young chicks, Corncrakes were found to move away from mowers far and fast enough to avoid being overtaken, provided that an escape route to a refuge area was available. During mowing of meadows from the outside inwards (O-I), chicks stayed in the isolated plot of unmown grass until the last few swaths remained to be mown and 55% were killed. Mowing from the centre of the meadow outwards (O-I) has been reported to reduce chick mortality because chicks are able to escape to unmown cover outside the meadow without leaving the shelter of tall grass. However, the present study showed that chick mortality was also lower (32%) during I-O than O-I mowing when the grass bordering the plot being mown had already been cut. In these circumstances the proportion of chicks that escaped was highest for the oldest chicks and when the width of the mown strip that the birds have to cross to escape was narrow. Chicks were less likely to be killed by I-O than O-I mowing even when the width of open ground to be crossed was similar for both methods. It is estimated that leaving refuge strips of unmown grass would reduce chick mortality when there is little natural escape cover at the edges of meadows being mown I-O.