Attraction of kestrels to vole scent marks visible in ultraviolet light

IN northern Europe, broad four-year oscillations in small rodent and raptor populations are synchronous over hundreds of square kilometers1–6. Crashes in vole populations can induce wide emigration (> 1,000 km) of their predators7 –9, but almost nothing is known about how predators rapidly detect areas of vole abundance. Here we report on laboratory and field experiments on voles (Microtus agrestis) and kestrels (Falco tinnunculus). Voles mark their runaways with urine and faeces, which are visible in ultraviolet light. Wild kestrels brought into captivity were able to detect vole scent marks in ultraviolet light but not in visible light. In the field, kestrels hunted preferentially near ex…