[Blood parasites of birds on the White Sea-Baltic migration route. 4. The ecological aspect].

The effect of some ecological factors on the infection of birds with blood Protozoa was studied. Most favourable conditions for circulation of Haemoproteidae on the Kurish Spit were recorded in July. The possibility of the infection of young small passerine birds from the first broods with Haemoproteidae is most high first of all at the expense of their longer stay in the nesting territory in the period of the active transport of parasites. The presence of Leucocytozoidae in Kurish populations is explained mainly by the distribution of birds. The registration of Leucocytozoidae from birds on the Kurish Spit in spring and autumn is the result of the flight of extensively infected northern populations. It is noted that a constant change in the populational composition of the ornithofauna during seasonal migrations should be taken into account when studying the parasites of wild birds. Otherwise the characteristic features of the circulation of parasites in the region in question can be distorted as a result of the overlap of data on the infection of birds of different populations. The dependence of the infection on sex and size of birds--hosts and the role of the nesting period in the distribution of some Haemosporidia are analysed.