Effect of winter temperature and maize food abundance on long-term population dynamics of the wild boar Sus scrofa

In a few recent decades, population increase of the wild boar has been evidenced in various European countries. As the result of this increase, the wild boar has expanded into farmlands, especially in some regions, where the cultivated maize constitutes the main source of its diet through the larger part of the year. The effect of winter weather and land use changes on the expansion of wild boar was analysed in a farmland in southern Poland. Over 21 years (1985-2005) in the study area of about 681 km2 a rapid increase in the number of harvested wild boars was recorded. While in the middle 1980's, there were only about 40 animals harvested per hunting season, in 2005 the number increased to 180. The rapid increase was, in general, correlated positively to the increasing surface area of the maize crops from 205 ha (0.9%) in 1985 to 3212 ha (14.9% of arable lands) in 2004. However the correlation between the increase of the average late winter (February/March) temperature and the number of wild boars seems to be negative and contrary to our expectations, the numbers of wild boars were found to be higher under the lower temperatures in that period of the year.