The Effects of Abatement Efforts on Wild Pig Behavior

By: Josh Helcel, Extension Associate

Texas A&M Natural Resources Institute

Wild pigs (Sus scrofa) are notorious for their ability to learn from past experiences and evade control efforts.  Groups of wild pigs that are not pressured often increase their diurnal activity and become more active during the day time (Gundlach 1967).  However, as abatement pressures increase wild pigs can alter their behavior to become more active at night and other behaviors can modify as well (Stegeman 1938, Hanson and Karstad 1959, Choquenot et al. 1996, Waithman 2001, Pei 2006).  This article will discuss various effects abatement techniques can have on wild pigs, and will recommend strategies that can help to minimize behaviors including trap aversion and escape when enacting control efforts for wild pigs.

Hunting Can Accelerate Wild Pig Birth Rates

It is accepted that sport hunting wild pigs alone will not significantly reduce populations.  Perhaps less apparent is that human activities such as hunting can influence evolutionary characteristics at both the population and species level (Darimont et al. 2009).  A good example of this has been observed in deer species (Odocoileus sp.); whereas high rates of trophy harvest were shown to lead to smaller overall horn size and body mass over time (Coltman et al. 2003).  In wild pig populations, however, high hunting pressure doesn’t necessarily lead to reduced body sizes or smaller tusks.  Extensive monitoring of wild pig populations over 22 years found that high hunting pressure can actually cause wild pigs to shorten their gestation period by as much as 12 days per cycle (Gamelon et al. 2011).  This acceleration is further compounded by increased conception rates of sows within their first year of life when populations are subjected to intense hunting or other abatement pressures (Gamelon et al. 2011).  Essentially, wild pigs may breed earlier and produce offspring more quickly when subjected to hunting pressure.  Given this novel survival strategy, it becomes more understandable why a state like Missouri banned completely the sport hunting of wild pigs on conservation lands.

 

Research indicated that wild pig sows subjected to high hunting pressure had higher conception rates in their first year and produced offspring up to 12 days sooner than normal gestation.

Wild Pig Adaptations to Aerial Gunning

Aerial gunning is an effective population reduction strategy unless limited by topography or dense canopy cover (Campbell et al. 2010).  However, previous research has shown that wild pigs can intelligently adapt their behavior to avoid detection and flushing by helicopters (Saunders and Bryant 1988).  It might be assumed that these animals would simply disperse from their home range in response to aerial gunning efforts.  In fact, research indicated the opposite in that core area and home range sizes did not alter either before or after enacting aerial control (Campbell et al. 2010).  Rather, wild pigs can adapt to aerial gunning by seeking dense cover and refusing to flush from it despite concerted efforts by the pilot and crew.  

Instead of flushing, some wild pigs have adapted to evade helicopters by holding within dense cover. 

 

What is significant about this behavior is that until relatively recently wild pig populations had not encountered significant predation from above their line of sight.  Despite this, they have quickly adapted to be capable of intelligently evading a formidable 5000 pound “aerial predator” that otherwise would seem to have every advantage.  The intelligence and adaptability of wild pigs are key factors that compound effective control (Sweeney et al. 2003), and this is again evidenced by their potential to evade aerial gunning efforts.

Trap Aversion

Research has long documented trapping as an effective population reduction technique, with 70-80% reductions in populations having been reported using this technique alone (Saunders et al. 1990, Vernes et al. 1999).  However, wild pigs can adapt to avoid traps altogether for a variety of reasons.  This can occur due to the size and type of trap used, but also can be attributed to inadvertently “educating” wild pigs through incomplete captures.  With the exception of solitary adult males (boars), wild pigs travel in social groups called sounders.  When trapping these animals, it is important to target and remove the entire sounder in a single trapping effort.  This is generally accomplished through a process of pre-baiting and conditioning the group over time to routinely enter a trap large enough to contain the entire sounder.  Corral style traps are often best suited for this, and research indicated this type of trap to be four times more effective than conventional box traps (Williams et al. 2010).  Box traps, while valued for their portability, usually only capture 1-3 animals at a time.  No matter what type of trap is used, incomplete captures can divide sounders and cause remaining pigs to avoid traps in the future. 

In order to minimize learned trap aversion due to incomplete captures, the goal of any trapping effort should be to target and remove the entire sounder of wild pigs.

Trap Escape

Wild pigs can also adapt to escape traps, and individuals that learn to do so often exhibit this behavior repeatedly.  Trap escapes can be accomplished through climbing, rooting, exploiting trap design flaws and even jumping considerable heights in excess of 4 feet.  It is important to construct and implement sound trap designs, and it is equally important to check traps as soon as possible following each trap night.  Many experienced trappers check their traps at first light and bring a firearm in order to harvest any residual pigs that may be near the trap site due to incomplete capture or escape.  The Texas A&M Natural Resources Institute recommends that corral traps be constructed with four to six 16’ cattle panels that have 5’ panel height and 4” mesh in order to minimize trap escapes.  It is generally not necessary to bury or trench paneling underground, but it is important not to leave any gaps at ground level or near the head gate.  Game cameras can be integral in monitoring wild pig activity at trap sites, and can also help to identify any modifications necessary in order to minimize the potential for trap escape.

Wild pigs will attempt to escape traps if given the opportunity. Ensure that traps are constructed properly and check traps at first light to help minimize trap escape attempts. (Image Credit: Andy James)

Conclusion

Wild pigs exhibit a variety of behavioral responses to abatement pressure.  Their intelligence and adaptability can complicate effective control, factors that are only compounded by their extreme fecundity.  It is important to select appropriate strategies as well as to adapt control techniques as necessary in order to minimize any potential issues which can reduce the success of abatement efforts.  This can undoubtedly be easier said than done, as is evidenced by the numerous and often remarkable ways in which wild pigs can evade control efforts despite the best technologies available to man.  However, best management practices including trapping, aerial gunning, strategic shooting, snaring, and the use of trained dogs remain proven tools that, when implemented in a combined approach, can successfully abate the damages associated with wild pigs.

 

Wild Pig Resources Listed Below are Available at the AgriLife Bookstore

– L-5523 Recognizing Feral Hog Sign– L-5524 Corral Traps for Capturing Feral Hogs
– L-5525 Box Traps for Capturing Feral Hogs

– L-5526 Placing and Baiting Feral Hog Traps
– L-5527 Door Modifications for Feral Hog Traps

– L-5528 Snaring Feral Hog

– L-5529 Making a Feral Hog Snare

– SP-419 Feral Hogs Impact Ground-nesting Birds

– SP-420 Feral Hog Laws and Regulations

– SP-421 Feral Hogs and Disease Concerns

– SP-422 Feral Hogs and Water Quality in Plum Creek

– SP-423 Feral Hog Transportation Regulations

– L-5533 Using Fences to Exclude Feral Hogs from Wildlife Feeding Stations

– WF-030 Reducing Non-target Species Interference While Trapping Wild Pigs
– ENRI-005 Wild Pigs Negatively Impact Water Quality: Implications for Land and Watershed Management

 

Click here for additional resources on wild pigs

 

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For educational programming or technical assistance with wild pigs please contact:

Josh Helcel, 512-554-3785, josh.helcel@tamu.edu

  

Literature Cited

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Coltman, D. W., P. O'Donoghue, J. T. Jorgenson, J. T. Hogg, C. Strobeck, and M. Festa-Bianchet. 2003. Undesirable evolutionary consequences of trophy hunting. Nature 426:655-658.

Choquenot, D., J. McIlroy, and T. Korn. 1996. Managing vertebrate pests: Feral pigs. Bureau of Rural Sciences, Australian Government Publishing Service, Canberra, Australia.

Darimont, C. T., S. M. Carlson, M. T. Kinnison, P. C. Paquet, T. E. Reimchen, and C. C. Wilmers. 2009. Human predators outpace other agents of trait change in the wild. Proc. Natl. Acad. Sci. USA 106:952-954.

Gamelon, M., A. Besnard, J. Gaillard, S. Servanty, E. Baubet, S. Brandt and O. Glmenez. 2011. High hunting pressure selects for earlier birth date: wild boar as a case study. Evolution 65(11):3100-3112.

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Saunders, G., and H. Bryant. 1988. The evaluation of feral pig eradication program during simulated exotic disease outbreak. Australian Wildlife Research 15:73-81.

Saunders, G., B. Kay, and R. Parker. 1990. Evaluation of a warfarin poisoning programme for feral pigs (Sus scrofa). Australian Wildlife Research 17(5):525-533.

Stegeman, L. J. 1938. The European wild boar in the Cherokee National Forest, Tennessee. Journal of Mammalogy 19(3):279-290.

Sweeney, J. R., J. M. Sweeney, and S. W. Sweeney. 2003. Feral hog. In ‘wild mammals of North America’. Johns Hopkins University Press: Baltimore, MD. pp. 1164–1179.

Vernes, K., C. N. Johnson and J. Mitchell. 1999. The effectiveness of trapping in reducing pig abundance in the Wet Tropics of north Queensland. In ‘Feral pigs: Pest status and prospects for control. Pp 51-56. Proceedings of a feral pig workshop. James Cook University, Cairns, March. Research Report No. 13. Cooperative Research Centre for Tropical Rainforest Ecology and Management, Cairns, Australia.

Waithman, J. 2001. Guide to hunting wild pigs in California. California Department of Fish and Game, Wildlife Programs Branch, Sacramento, California.

Williams, B. L., R. W. Holtfreter, S. S. Ditchkoff and J.B. Grand. 2010. Trap style influences wild pig behavior and trapping success. Journal of Wildlife Management 75(2):432–436.