Displays of vigilance in wild boar (Sus scrofa ussuricus) groups in a protected area of the central Sikhote-Alin

A study of a wild boar population’s vigilance was carried out 50–80 years following the creation of the Sikhote-Alin Nature Reserve, Russian Far East and the cease of hunting. The defensive behavior of the wild boar depends especially strongly on the tiger (Panthera tigris tigris) and the brown bear (Ursus arctos). Based on 298 encounters, the following responses were determined: (a) reactions of wild boars to stimuli associated with danger, (b) parameters of alertness (3.2 hours of measured time, frequency of observed postures and movements). Response features to different signals were also determined using snow-tracking. Nonparametric and, after normalization, parametric criteria were applied. Vigilance towards humans is maintained due to a generalized reaction to real danger (large predators) and probably because the wild boar population of the nature reserve is not isolated from the surrounding areas. In more than 70% encounters, wild boars detected danger by sounds accompanying movements (from almost 0.6– 0.8 km). Visual scanning of movements and the identification by smell are important in detecting the close presence of a predator, which is essential in the tiger’s usual hunting methods. The reaction to the smell of human or tiger tracks intensified during the periods of frequent visits by the predator to the wild boar’s habitat, as well as after its long absence, depended on the meeting place. The vigilance decreased during the periods of famine. Wild boars showed the ability to quickly extrapolate the direction of the movement of a dangerous object. Guards and boars over 2 years old in maternal groups were seen in 35.7% cases; in 16% cases, there was no obvious guard; in 48.3% the situation was not determined (for small groups in 89.9%). Wild boar guards in a calm situation spent an average of 8–9% of their time on vigilance when resting and 11–12% when grazing. Vigilance rates increased 16.2–41.3 times in different individuals and at different times in the same wild boars with the risk of a predator encounter or extraneous sounds. Only a small percentage (≤ 2%) of other individuals, with alternating vigilance in groups, complemented the groups’ general vigilance. Individual differences in vigilance at different times in the same wild boars were determined. Small average values of alertness (with frequent reactions) seem to be consistent with the hunting tactics of the tiger, which alternates pursuit of the wild boar with long cessations and hunting in other areas, as well as with the ability of the wild boar to react to an unexpected attack by a predator.