Sex ratio and age structure of wild boars (Sus scrofa) culled by leg snare trap in the Yamizo mountainous region of Tochigi Prefecture, Japan

Abstract

The wild boar (Sus scrofa) is one of the most widely captured animals in Japan, and the population culled using leg snare traps has been increasing in recent years. However, the characteristics of wild boars captured using this method remain unclear. This study was conducted to determine the sex ratio and age structure of the wild boars captured in the Yamizo mountainous region of Tochigi Prefecture for many years by examining the wild boars brought to a slaughterhouse in Nakagawa town. The male-to-female ratio was 1.37:1. To determine the age structure, the number of animals, including both males and females, in the 0-year-old group was low. In contrast, 83.9% of males were <2 years old, whereas 37.2% of females were ≥2 years old. Additionally, the age at which the probability of capture, calculated from this sample, was the highest, and was estimated to be 1.4 years for males and 2.1 years for females. As female wild boars attain sexual maturity and start breeding in less than one year of age, continuous capture of subadult or older female boars using leg snare traps is effective in controlling the population of wild boars.