During five years (1992–1996) the effect of age of collared flycatcher males on arrival time, quality of nest site, partial losses, feeding effort and reproduction were examined in the primaeval, mature (170–250 year old) oak-lime-hornbeam forest of Białowieża National Park. The males were divided into two age groups: males with brown primaries and wing covers were aged as young, and males whose wings were uniformly black were aged as old ones. Only the arrival date and the clutch size were significantly different between the groups of males but other breeding features were very similar. These results may be explained by a short life-span of flycatchers and by conditions in the Białowieża National Park. A surplus of good natural cavities reduced competition between young and old males, and a surplus of food could reduce differences in foraging abilities. A high predation rate was the main cause of nesting losses. In such conditions, the strategy to take each opportunity of reproduction may lead to high life time reproduction success and can reduce potential differences in breeding success young and old males.
Toxoplasma gondii Nicolle et Manceaux, 1908 is an apicomplexan parasite with a worldwide distribution. It is of great medical and veterinary importance because it may cause abortion or congenital disease in its intermediate hosts, including man. The European bison, the largest herbivorous animal in Europe, is a species that has been saved from extinction. Twenty-four of 95 examined sera of the European bison (Bison bonasus bonasus) from the Białowieża Forest, Poland collected from 2008 to 2011 were found to be positive for the presence of T. gondii-specific IgG antibodies using a direct agglutination test, with the antibody titre in positive animals ranging from 40 to 18000. Statistically significant differences were observed only between years of sample collection. This is the first report on T. gondii in lowland European bison living in the natural environment.