Wild boar behaviour during live-trap capture in a corral-style trap: implications for animal welfare

Abstract

Background: Wildlife traps are used in many countries without evaluation of their effect on animal welfare. Trap-capture of wild animals should minimise negative effects on animal welfare, irrespective of whether the animals are trapped for hunting, research, or management purposes. Live-trap capture of wild boar (Sus scrofa) followed by killing inside the trap by gunshot is a recently introduced but disputed hunting method in Sweden. Approval of trap constructions is based on gross necropsy findings of 20 trapped and shot wild boars. For improved animal welfare evaluation, our aim was to study wild boar behaviour during live-trapping in a 16 m² square corral-style trap. Behavioural assessments were conducted after filming 12 capture events of in total 38 wild boars (five adults, 20 subadults, 13 piglets). Selected behavioural traits were compared with pathological changes (trap-related lesions) found at necropsy of the 20 subadults, to determine if these variables were useful proxies of capture-induced stress in wild boar.

Results: The wild boars spent less time resting in the evening than in the night and morning. Using Friedman's ANOVA, there was an overall difference in the time spent foraging. However, we only found a difference between the evening and morning in the Wilcoxon matched pairs test after the Sequential Bonferroni correction, where the wild boars spent more time foraging in the evening than in the morning. Single captured individuals showed more escape behaviours and reacted more strongly to external stimuli than individuals captured in a group. It was more common for animals to charge against the mesh walls of the trap upon human approach compared to upon initial capture when the trap door closed. Trap-related pathological findings due to trauma were documented in 13 of the 20 subadults that were necropsied. Behavioural alterations indicative of capture-induced stress (e.g. charging into the trap walls) were documented in trapped wild boars with no or minor physical injuries (e.g. skin abrasions, subcutaneous haemorrhage).

Conclusions: Behavioural assessment provided valuable information for determination of capture-induced stress in wild boar when evaluating live-trapping in a corral-style trap, whereas pathological evaluation through necropsy did not fully reflect the animal welfare aspects of live-trapping. We emphasize the inclusion of species-specific behavioural data assessment for evaluation of capture-related stress during live-trapping and for testing of new trap constructions before approval.

Keywords: 3R; Ethogram; Health; Hunting; Management; Refinement; Stress; Sus scrofa; Trapping; Wildlife.

Fig. 1

Corral-style trap (JP BUR, https://www.jpbur.se) for live-capture of subadult wild boar in Sweden. This trap was tested based on pathological examinations as part of an assignment from the Swedish Environmental Protection Agency (SEPA) to the Swedish University of Agricultural Sciences (SLU) to evaluate new live-traps for wildlife capture. In the present research study, we analysed behavioural data from films recorded during captures for the trap evaluation

Fig. 2

Distribution of behaviours of wild boar captured in a corral-style trap. Nine capture events with data from the evening, night and morning were included in the analysis. The median (square), maximum and minimum (whiskers) and the 25–75% quartiles (box) are shown

Fig. 3

Number of charges by captured wild boar into the mesh wall or door of a corral-style trap. Charges upon initial capture (11 capture events) and upon approach by the wildlife manager (7 capture events) are shown as the median (square), maximum and minimum (whiskers) and the 25–75% quartiles (box)

Fig. 4

Wild boar charging against the mesh walls of the corral-style trap