Physiological condition and blood parasites of breeding Great Tits: a comparison of core and northernmost populations

Abstract

Several studies have shown considerably poorer breeding success of Great Tit Parus major populations in northern Finland than in mid- and western Europe. The aim of this study was to find out whether the poor success is linked to physiological condition and loads of blood parasites. This was done by comparing several condition indices, blood parasite prevalences and infection intensity in two populations, northern Finland (66°N) and Latvia (56°N). It was found that Great Tits had smaller clutches and produced fewer fledglings in northern Finland than in Latvia. Great Tits breeding in northern Finland had higher levels of haematocrit and higher concentrations of heterophils, lymphocytes, eosynophils and total globulin, while they had lower albumin/globulin ratios, which indicate higher levels of physiological stress and increased probability of infectious diseases. Surprisingly, Great Tits had lower blood parasite prevalence and the intensity of infection in northern Finland than in Latvia, while parasite vectors were more abundant in northern Finland.