Social behaviour, reproductive biology and breeding succes of Alpine Rock Ptarmigan Lagopus mutus helveticus in northern Italy

We monitored social behaviour, nest site selection, clutch size and survival, and breeding success (number of fledglings per successful hen in late August) in two Alpine Rock Ptarmigan Lagopus mutus helveticus populations in the South-central Alps, Italy, 1992-97. Phenology of flock formation and territory occupancy was similar as in northern populations, and, in spring, cocks outnumbered hens in most years. Not all cocks found a partner, but all paired cocks appeared to be monogamous. Few hens that lost their eggs during incubation laid a repeat brood. Adult hens (more than one year old) laid larger clutches than yearlings and clutch size was larger for first than for repeat broods. Nest losses were high (50%) and mainly due to predation of the incubating hen or her eggs. Probability of nest loss was not significantly affected by the amount of cover around the nest or nest type. Average clutch size, nest predation rates, and breeding success fluctuated annually, and clutch losses were higher in years with poor weather during incubation, suggesting that stochastic factors (weather, predators) strongly influenced brood survival in Alpine Rock Ptarmigan.