Temporal dynamics of grouse populations at the southern edge of their distribution

Studies of grouse conducted at northern latitudes have shown that tetraonids frequently exhibit cyclic fluctuations in abundance but little is known about the dynamics of grouse species at the southerly edge of their range. Hunting statistics from four species of grouse based on 30 yr of data collected from 210 hunting areas were examined from the Dolomitic Alps in the province of Trentino. These data were summed to represent 18 time series from discrete mountain groups. Analyses identified cycles of ca 5 yr in the minority of rock ptarmigan Lagopus mutus and hazel grouse Bonasa bonasia populations. These cycles only showed significant negative autocorrelation at half the cycle period and were classified as phase-forgetting quasi-cycles. Cycles were not found in time series of black grouse Tetrao tetrix or capercaillie Tetrao urogallus. Correcting time series for hunting effort or hunting restrictions tended to increase the proportion of populations that exhibited cycles but no difference in the strength of second order density dependence. A linear first order density-dependent autoregressive model described the dynamics of most of the populations with the exception of a proportion of rock ptarmigan and black grouse populations where a non linear first order model provided the best fit. We compare the findings with studies conducted in Finland and suggest possible reasons for the reduced tendency to cycle in the populations of southern Europe.