Seasonal infection patterns inWillow Grouse(Lagopus lagopus L.) do not supportthe presence of parasite-induced winter losses

We examined the hypothesis that endoparasites ofWillow Grouse (Lagopus lagopus L.)affect host winter losses, by examining two samples ofWillow Grouse collected in earlyautumn and late winter. Body condition of juvenile birds improved from September toFebruary, but parasite-induced hostmortalities among hosts in poor conditionwere probablynot the cause. If heavily infected hosts were removed disproportionately from thehost population, thenumber of parasite species per host together with their prevalence andintensities should be lower in winter than in autumn. While overall parasite burden waslower in winter than in autumn, most parasite species showed no seasonal decrease inprevalence or intensities. Only one species, Trichostrongylus tenuis, showed a seasonaldecrease in both prevalence and intensity.Mean intensities of Eimeria spp. decreased significantlybetween seasons, while prevalence did not. If mortality rates were higheramong heavily infected hosts, parasite aggregation should be lower in winter than in autumn,but no such pattern was found, except for Eimeria spp. Thus, the results presentedin this study yield no clear evidence for parasite-induced mortality inWillow Grouse betweenautumn and late winter.

Espen Schei, Per R. Holmstad, Arne Skorping, Ornis Fennica 82:137-146. 2005