Fox and martens - are they really opportunistic feeders? A case of beetles and other arthropods occurrence in carnivores" diet

The main goal of the investigation was to assess and compare insects' abundance in diet of fox (Vulpes vulpes) and martens (Martes martes, Martes foina). The research was carried out in three national parks and in the city of Kraków, all located in the southern Poland. The collection of carnivores' faeces took place between 2002 and 2007. The total number of samples was 517 for foxes and 747 for martens. 59 insects species were recognised in 19% of samples. Forward selection of canonical correspondence analysis revealed factors that were carnivore species, place of collection which both described 89% of variance of insect species environment relations. Martens as a variable seemed to be the most influential on the composition and relative abundance of all insect assemblages (Monte Carlo test F=3.94, P<0.001). Moreover, the place of collection was an important factor (Monte Carlo test F=3.03, P=0.002 and F=2.18, P=0.002, respectively for Kraków and the Tatra Mountains). Martens fed most often on nest insects species, whereas foxes chose large beetles. The diagram of canonical correspondence analysis confirmed that distribution of specific groups of arthropods depended on carnivore feeder as well as occupied habitat.