A high level of nest predation observed in a large Sand Martin (Riparia riparia) colony

During the 2016 field season, we investigated the influence of intense nest digging predation at a Sand Martin colony that is situated in natural habitat along the Tisza river. Over this season, foxes dug a large number of holes which either partly or fully destroyed 39% of burrows in a large colony, comprising over 1,500 pairs. This high level of predation caused death and/or injury to between 7% and 44% of breeding individuals and lowered the reproductive success of the colony as on average 20% (between 5% and 43%) less nestlings were fledged. The level of digging showed a negative exponential growth with burrow density. Our observations show that the burrows were most at threat between 0 m and 0.4 m from the top and between 0 m and 1.4 m from the bottom of the wall. These observations show that it is critically important to decrease the number of foxes and other potential nest predators, whose numbers have increased well above ‘natural’ levels over the last decade, in regions where Sand Martins are nesting as this species is in drastic decline.