Fitting a bivariate negative binomial model to the distribution of bird lice (Phthiraptera, Mallophaga) parasitizing the pheasant (Phasianus colchicus L.)

The frequency distributions of seven lice species: Amyrsidea perdicis megalosoma (Overgaard, 1943), Uchida phasiani Modrzejewska et Zlotorzycka, 1977 (suborder Amblycera), Goniocotes chrysocephalus Giebel, 1874, Zlotorzyckella colchici (Denny, 1842), Lipeurus maculosus maculosus Clay, 1938, Reticulipeurus mesopelios colchicus (Clay, 1938) and Lagopoecus colchicus Emerson, 1949 (suborder Ischnocera) parasitizing the pheasant (Phasianus colchicus L.) were characterized with various statistical parameters (mean, range, prevalence and standard deviation) together with three indices of parasite aggregation: parameter a of the negative binomial distribution, coefficient of dispersion (c.d.) as a dispersion to mean ratio (or s/x) and index of discrepancy (D of Poulin's index). A complex set of measures of aggregations confirmed the aggregated distributions of all parasite species; in all the series analysed the bird lice distributions fit the negative binomial model. Two parameters a and D of Poulin were correlated, i.e. high values of a were associated with low values of D.