REPRODUCTIVE OUTPUT, POPULATION-STRUCTURE AND CYCLIC DYNAMICS IN CAPERCAILLIE, BLACK GROUSE AND HAZEL GROUSE

We studied annual changes in the reproductive output of cyclic populat ions of Capercaillie Tetrao urogallus, Black Grouse Tetrao tetrix- and Hazel Grouse Bonasa bonasia in Finland. The data consisted of route c ensuses made in early autumn in 11 provinces during 1964-1984. Records separated adults and young of the year. First, young bird numbers wer e regressed against adult densities. On a natural logarithmic scale th is relationship was linear. No differences in slope of the regression were detected among the 11 provinces within any of the species. The re gression slopes for the three species were: Capercaillie 1.24, Black G rouse 0.91 and Hazel Grouse 0.87. The reproductive output was defined as the residuals of the species-specific regression models in each pro vince. It correlated with the population cycle, so that high reproduct ive output preceded high total numbers the next year. Using a simple s tage-structured transition matrix model with delayed, second-order den sity dependence in breeding success, and differential fecundity and su rvival between first-time breeders and older birds, we were able to cr eate cyclic population fluctuations closely matching those documented for Finnish grouse.