Rätti, O. & Alatalo, R.V. 1997: The dynamics of blood parasite infections in black grouse Tetrao tetrix in Finland. - Wildl. Biol. 3: 280.
Finnish black grouse Tetrao tetrix populations fluctuate regularly with a cycle length of about six years. Parasites can theoretically affect growth rate of a host population. Therefore, parasites may be regulating black grouse population density and causing the cyclic pattern. A black grouse population in central Finland was studied during 1988-1994, the length of a population cycle. Blood samples were taken from 284 black grouse 391 times to examine for haematozoan parasites. All samples were examined at the International Reference Centre for Avian Haematozoa by G.F. Bennett. The most common blood parasites were Leucocytozoon lovati and microfilaria. Additionally, some individuals were infected by Haemoproteus mansoni and Trypanosoma avium. The prevalence of L. lovati varied annually between 23 and 70%. The prevalence of microfilaria varied from 11 to 48%. The probability of an individual to have a Leucocytozoon infection decreased with increasing age and was highest in yearlings (50%). The incidence of microfilaria was lowest among yearlings (12%) but increased with age. The prevalence of microfilaria in older black grouse correlated negatively with population density, being lowest during peak grouse density. Leucocytozoon prevalence was not correlated with population density but reached a peak during the increasing phase of the population cycle. There was no evidence that blood parasites affected survival of black grouse or population dynamics of the species.
Key words: black grouse, haematozoan parasites, population dynamics, survival, Tetrao tetrix
Osmo Rätti, Arctic Centre, University of Lapland, P.O. Box 122, FIN-96101, Rovaniemi, Finland
Rauno V. Alatalo, Department of Biological and Environmental Science, University of Jyväskylä, P.O. Box 35, FIN-40351, Jyväskylä, Finland