The effects of hunting and landscape structure on wild boar behavior, social structure and physiology in urban, agricultural and natural areas in Israel

Achiad Davidson

In recent years, in Israel and in many places in the world, wild boar (Sus scrofa) have expanded their geographical distribution to new areas and their population density has increased, especially near agricultural and urban areas. The increase in the population of wild boars and their expansion into new areas increases the conflicts between wild boars and humans. Hunting is the oldest and most common management action used to control wild boar populations around the world and in Israel.
Recent studies demonstrated that high hunting pressure causes juvenile females to reproduce earlier, resulting in shorter generation periods, leading to higher reproduction rates. This cause and effect may be one of the main reasons for the rapid population growth of wild boar populations.
This study attempts to compare and evaluate the effects of hunting on wild boars’ behavior, social structure, and physiology in four different land uses in the Carmel region in northern Israel: urban areas with and without hunting, agriculture areas with high hunting pressure and nature reserves with no hunting.

In recent decades human populations have increased substantially and expanded in urban and rural areas, resulting in increased human-wildlife conflicts. Concomitantly, wild boar (Sus scrofa) populations have increased in the last 40 years worldwide, particularly in the vicinity of agricultural and urban areas. The consequences of these population increase include elevated economic costs resulting from boars transferring epidemics to livestock and humans and damage to gardens in urban areas and agricultural crops. For instance, the estimated annual costs of damage to agriculture by wild boars in Europe is €80,000,000. The most common and widespread management tool that is used in attempts to control wild boar population increases is culling. It has been recently estimated in Europe that more than 3 million wild boars are hunted yearly. However, despite the high hunting pressure, the number of wild boars continues to grow. Recent studies demonstrated that high hunting pressure causes juvenile females to reproduce earlier, resulting in shorter generation times, leading to higher reproduction rates. This cause and effect may be one of the main reasons for the rapid population growth of wild boar populations.

This study attempts to compare and evaluate the effects of hunting on wild boars behavior, social structure and physiology in four different land uses in the Carmel region in northern Israel: urban areas with and without hunting, agriculture areas with high hunting pressure and nature reserves with no hunting.

To study the risk perception of wild boars while foraging I evaluated the combined effects of hunting and different land-use types on their behavior. I installed corn-supplemented feeding devices in four land-use types – hunting combinations: urban areas with and without hunting, and rural areas, namely agricultural areas with hunting, and nature reserves without hunting. The results show that boars in agricultural areas, which are exposed to high hunting pressure, showed significantly higher risk perception and reduced foraging compared to boars in nature reserves. However, surprisingly, the results further suggested that wild boars in urban areas perceive substantially lower risk of predation regardless of hunting activities while foraging, compared to wild boars in rural areas (nature reserves and agriculture).

high hunting pressure causes juvenile females to reproduce earlier. This cause and effect may be one of the main reasons for the rapid population growth of wild boar populations.

To further understand the risk perception of wild boars in rural areas and to account also for their social structure, I installed motion-triggered cameras along movement trails. I identified the age and sex of individual wild boars and the size and structure of their social groups, and quantified hunting intensity in agricultural areas (hunting permitted) and nature reserves (hunting prohibited). Results indicated significant differences in the vigilant behavior of wild boars between agricultural areas and nature reserves. In agricultural areas, adult females were significantly more vigilant compared to adult males. Additionally, in these areas we found significantly more adult males and less family groups with females. Furthermore, male yearlings were significantly more vigilant in agricultural areas compared to female yearlings. Male yearlings tended to roam significantly more with family groups in agricultural areas compared to nature reserves, where they tended to roam alone or in groups.

To explore the physiological effects of hunting, I compared steroid hormone levels in the hair of female wild boars from populations exposed to high hunting pressure with those exposed to substantially lower hunting pressure. Furthermore, I tested steroid hormone levels from hair of female wild boars roaming alone or as part of a group. I found no hormonal signs for stress in the hunted boars. Cortisol levels were low in both high and low hunting groups. Yet, progesterone levels were higher in females that were exposed to high hunting pressure. Additionally, females roaming in a group also had higher progesterone levels compared to females roaming alone.

In conclusion, this study presents evidence that increased predation risk, caused by human hunting, leads to higher risk perception (e.g., increased vigilance behavior and reduced foraging), variations in social structure and higher reproductive hormones in rural wild boar populations. The results further suggested that urban boars show significantly lower risk perception compared to rural boars possibly due to habituation of urban boars to humane presence.

Moreover, these results provide evidence that high hunting pressure causes significant changes to the behavior and social structure of wild boars, however it does not cause chronic stress, but positively impacts a reproductive hormone in female wild boars. This response may be one of the reasons leading to the worldwide rapid population growth of wild boars, despite the high hunting pressure they are exposed to, and provides a better understanding of the biology of wild boars.

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