Hoe hoog is laag genoeg, en omgekeerd: predatie van Vossen Vulpus vulpus in kolonies van Oeverzwaluwen Riparia riparia

Sand Martins in a quarry were depredated by Red Foxes when nests were within 70 cm from the foot of the quarry, or less than 50 cm below ground level. Sand Martins anticipated predation from below by digging holes in the upper third of the wall, preferably with water at the base of the cliff. In shallow quarries predation from above caused havoc among Sand Martin nests when the vegetation cover was thin or lacking. Foxes started digging from above when there were young; digging was directed at nest chambers, apparently homing in on begging nestlings. Safe quarries for nesting Martins should include water at the base, cliffs exceeding 130 cm and a thick vegetation cover on top of it.