SYNCHRONY IN TETRAONID POPULATION-DYNAMICS

1. We studied temporal and spatial synchrony of population fluctuations in the capercaillie (Tetrao urogallus), the black grouse (Tetrao tetrix) and the hazel grouse (Bonasa bonasia) in Finland. 2. The data consist of route censuses (20 000-30 000 km annually) performed in 11 provinces during 1964-83, The population data for the three species in each province were standardized to zero mean and unit variance. 3. Cross-correlation analysis indicates that population dynamics of the three species in every area are in rather good temporal synchrony. Moreover, with the aid of k-means clustering, the 11 provinces could be merged into four regions, indicating large-scale synchrony in dynamics of the three tetraonid species. 4. Because it is obvious that this synchrony cannot be due only to the similar life histories of these species, we explored whether it could be influenced by a common synchronizing factor affecting all the species simultaneously. In order to do this we used a Leslie matrix-based simulation approach. In this model there is a stochastic hit of breeding failure at a given average interval. This failure was shown to synchronize the population dynamics of the species with primarily different life tables.