ИСТИНА

Reasons of the irregular distribution of parasites on their hosts represent an important question in ecophysiology. We examined for ectoparasites 28 passerine bird species (n>= 10) in the tropical forest of the Southern Vietnam. Most of the chewing lice species showed typical aggregated distribution on their hosts with few hosts keeping most of parasite population and many hosts being free of parasites. However for one species of host, black-and-red broadbill (Cymbirhynchus macrorhynchos) we found unusual infestation parameters of its parasite chewing lice Myrsidea claytoni with 100% prevalence and relatively high intensity. To test the conditions affecting the parasite load (chewing lice, feather mites and louse flies), i.e. external factors (year of study, habitat) and internal parameters of the host (basal metabolic rate, blood indexes, brood patch status, molt stage, body mass) we performed GLM analysis. Despite the small sample size (31 birds), we revealed significant positive relation between parasite load of M. claytoni and the lymphocyte/erythrocyte blood index in the black-and-red broadbill. Interestingly another chewing lice species Guimarasiella sp. inhabiting the same host did not show significant relations with blood characteristics. We explain the observed contrast by the different life style of the chewing lice. M. claytoni belongs to the motile blood foraging Amblycera chewing lice, while Guimarasiella sp. represents less motile feather consuming Ischnocera lice. We suggest that some features in broadbill behavior should explain the easiness of chewing lice exchange within host population when mostly the defensive (including immune) response of the host limits the parasite proliferation.