FORAGING BY PINE MARTEN MARTES MARTES IN RELATION TO FOOD RESOURCES IN BIALOWIEZA NATIONAL-PARK, POLAND

Feeding habits of pine marten Martes martes (Linnaeus, 1758) were stud ied in 1985 - 1992 in the pristine forests of Bialowieza National Park , eastern Poland, The study covered 5 years of moderate numbers of for est rodents and 2 years of outbreak and crash. In 1735 analysed seats, rodents (Clethrionomys glareolus, Apodemus flavicollis, and Microtus sp.) were staple food for martens, constituting from 50% of biomass co nsumed in June to over 90% in October - November, Birds (mainly thrush es and woodpeckers) were captured by martens mainly in spring and summ er (up to 37% biomass in June). Vegetable matter (Rubus berries, Sorus aucuparia fruit, mushrooms) was frequently eaten in July - October (u p to 17% biomass in September). Ungulate carcasses were scavenged in w inter. Marten preferred the remains of wolf and lynx kills and avoided ungulates that had died from undernutrition and/or disease. Between-y ear variation in marten diet was shaped by variation in rodent (especi ally bank vole) numbers. Percent of bank vole biomass in marten diet i n autumn-winter was determined by the summer-autumn numbers of these r odents. Martens' consumption of mice in the cold season did not reflec t the changes in mouse numbers, but it was positively correlated with their preying on bank voles. Spring numbers of mice determined the per centage of biomass of mice in marten diet in spring-summer. Snow cover significantly decreased martens' preying on C. glareolus, but not A. flavicollis and Microtus sp. In the cold season, insectivores and ungu late carcasses were crucial alternative food for the pine marten and t hey compensated for the decreased availability of rodents. In spring a nd summer, birds and fruit were alternative food, the consumption of w hich negatively correlated with the consumption of rodents. Snowtracki ng showed that in their search for prey, martens utilized both fallen and standing trees, and moved on the ground as well as in the forest c anopy. Over 90% of all recorded attacks were on rodents. Marten attack ed rodents 4.1 times/km of trail but 35% of attacks failed.