Interspecific den sharing: a study on European badger setts using camera traps

Many mammals, both potential competitors and preys, have been reported to use the complex burrow system of European badger Meles meles setts as shelter, mainly in northern Europe and during winter, when badgers are lethargic. Nonetheless, until recent times observations of den sharing have been largely restricted to anecdotal information, because of the mainly nocturnal activity of most sett occupants. Using camera-trapping, we investigated both the mammal fauna associated with 24 badger setts located in northern and central Italy, and seasonal variation in the composition of specific assemblages, without interfering with the occupants' activity. Trapping effort was 1,605 camera trap-days from December 2010 to December 2013. Badgers (two to six individuals per sett) shared their setts with a total of eight mammal species: crested porcupine Hystrix cristata, Eastern cottontail Sylvilagus floridanus, red fox Vulpes vulpes, pine marten Martes martes, stone marten Martes foina, wood mouse Apodemus sp., brown rat Rattus norvegicus and coypu Myocastor coypus. Den sharing was observed throughout the year, with a significant reduction of sharing during winter, when badgers were probably induced to move to alternative setts to avoid breeding porcupines. Eastern cottontails used badger burrows permanently and, at least in one occasion, reared their pups inside, although they can be easily preyed upon by badgers. Badger sett sharing may have favoured both the recent northward expansion of crested porcupines and settling of introduced cottontails in agricultural habitats.