Population density of the wild boar (Sus scrofa) in south-western Poland in 1981–2020

Abstract

The study is based on the analysis of hunting bag data from the years 1981–2020. In 1980–1990, 38 016 wild boars, whereas in 1991–2000, 43 490 wild boars were culled (14.4% increase) in south-western Poland (29 358 km2, forests comprise 28.6%). In 2001–2010, there were 69 052 individuals harvested (58.8% increase in relation to the previous decade). In 2011–2020, the harvest was 3-fold higher in relation to the previous decade and 5.6-fold higher in relation to 1980–1990. During the years 1981–1990, an estimated number of 51–100 wild boars were recorded only in five hunting districts, whereas there were 23 such districts in the next decade. After a population expansion in 2001–2010, there were 32 districts, each one with 101–200 wild boars. Ecological population densities (per forest area) of the wild boar was spatially greatly varied in south-western Poland, ranging from 9.1 ind./1000 ha in extensive woodlands of the Lower Silesian Forests to as much as 147.2 ind./1000 ha in the Wrocław Plain dominated by farmlands with forest fragments. The crude density was much lower and much less spatially varied than the ecological density; it was the lowest (7.4 ind./1000 ha) in the West Sudeten Mts. and the highest, 23.8 ind./1000 ha in the East Sudeten Mts. When only ecological density is calculated, a strongly distorted picture may emerge, where the highest density will always be in deforested areas with forest fragments, whereas it will be inevitably the lowest in the most afforested ones. The crude density will, therefore, reflect much better the actual population densities. In comparison with the line transect track index, the hunting bags analysis provide similar population density estimates, whereas in the comparison with the block count census, population densities based on the hunting bag analysis are underestimated. However, it should be emphasised that density estimates based on hunting bag analysis will always be lower than the real densities, as not all animals are harvested in a given population. The following ecological variables may shape wild boar population density in south-western Poland: food resources (maize, mast); temperature (winter and early spring); precipitation (snow and rainfalls); and diseases (especially African swine fever).