WHY LEMMINGS HAVE INDOOR PLUMBING IN SUMMER

The faeces and urine of microtine rodents are visible in ultraviolet l ight, and diurnal raptors, such as European kestrels (Falco tinnunculu s) and rough-legged buzzards (Buteo lagopus), have the ability to see in ultraviolet light. It has been reported that in Fennoscandia, these raptors use this ability to concentrate their hunting activity in spr ing on areas where microtines are abundant. We hypothesized that in ar ctic tundra areas in summer, intense avian predation pressure and shor t vegetation should select for microtine behaviour that would minimize their exposure to these raptors. We dug up 62 collared lemming (Dicro stonyx groenlandicus) burrows in the Canadian Arctic and all had under ground latrines. Latrines are not hidden underground in winter, when l emmings live under the snow, build nests above ground, and defecate ab ove ground, nor does this occur in microtine species living in tempera te areas, where summer vegetation growth is greater. Thus, high predat ion risk may influence not only where prey forage but also where they defecate.