HATCHING SUCCESS OF LAPWINGS ON FARMLAND - DIFFERENCES BETWEEN HABITATS AND COLONIES OF DIFFERENT SIZES

1. Nest site choice and reproductive success of lapwings was studied during 1988-90 at a farmland site dominated by cereal crops in central Sweden. 2. The most important factor causing breeding failures was farming operations, which accounted for 85% of all nest losses. Difference in hatching success between habitats; unsown tillage (9% hatching success), sown tillage (78%), fallow fields (31%) and grassland (67% hatching success) was an effect of different farming practices. 3. Only 13% of the females were estimated to hatch a first clutch, but a majority (66%) of the females that lost the first clutch was estimated to lay a replacement clutch (67% hatching success), giving an estimated proportion of 55% females hatching a clutch. 4. Although most failures were caused by farming practices, predation accounted for 14% of nest losses. Predation risk was negatively correlated to the number of close neighbours (R2 = 90%), indicating that the density of nests in the colony was very important. 5. There was also a general anti-predator effect in large colonies, which was independent of the number of close neighbours, since nests in large colonies (>5 nests) were less likely to be robbed than solitary nests and nests in small colonies (2-5 nests). 6. Nest survival was higher at sites far (>50 m) from trees or other perches suitable for avian predators than at those situated close to (<50 m) these perches, indicating that birds were important predators of lapwing nests. 7. Lapwings seemed to minimize the influence of avian predators by breeding in aggregations, 92% of the nests were found in colonies (up to 28 nests), and preferring nest sites far away from perches for avian predators. 8. Paradoxically, lapwings preferred to breed on tillage, which (when unsown) was the habitat with most nest losses. However, a majority of the failed breeders laid a replacement clutch and 57% of the females is estimated to hatch a clutch in tillage, which is slightly better than in other habitats.