Survival and Departure of Corncrakes Crex crex on Managed Breeding Grounds

Abstract

After losing their nests or broods due to mowing of grassland, ground-breeding birds may re-nest or disperse from the previous home-range. Breeding corncrakes are frequently affected by mowing of grasslands and often disperse over long distances afterwards. We studied the effects of mowing on departure rates of radio-tagged males from two river floodplain areas in Germany (LOV) and the Netherlands. Birds left from both study areas throughout the breeding season. Daily probabilities that birds survived and remained in the study areas varied between the study areas and within seasons, with lowest values in LOV in June 1998–2000, when mowing was most intensive. When mowing of corncrake habitats was almost completely postponed in LOV 2012–2015, males stayed more than three times as long as previously. Mowing had a strong direct effect on departure rates. The model results show that more than 50% of males died or dispersed within a week after mowing. At the same time, males which were not affected by mowing departed from all study areas, too. Postponed mowing increases the probability of males remaining at the breeding sites thus enabling them to re-nest or initiate second broods. Because dispersing birds can re-nest far away, assessing the situation of the population properly will require a large-scale approach.