Diet, body condition, and reproduction of Eurasian pine martens Mantes martes during cycles in microtine density

Winter diet, body condition, growth, reproduction, and age structure of pine martens Martes martes were studied during cycles in microtine density in south‐central Sweden. I analysed 398 scats collected in winters 1988 89 to 1996‐97. and 483 carcasses from martens trapped in winters 1989‐90 to 1992‐93. Microtines were the single most frequent prey category in the winter diet, and the consumption of microtines was correlated with microtine density. In the absence of microtines. pine martens increased the relative consumption of some alternative prey, most notably hares. Among adults, total food consumption, body condition, and reproductive success did not follow microtine density. Among juveniles, there were indications of lower total food consumption, smaller fat deposits, and higher trapping vulnerability, and among juvenile females also of lower body growth, when microtines were scarce. The data were, however, not consistent in this respect. I suggest that pine martens in the southern boreal region do not suffer from food shortage at microtine lows, and accordingly, that the demography of pine martens is independent of microtine cycles.