Assessing Various Predator Crossing Deterrents for Fence Line Management on A White-Tailed Deer Ranch in Southern Texas
In south Texas, predation of white-tailed deer (Odocoileus virginianus) fawns and nesting game birds like wild turkeys (Maleagris gallopavo) and bobwhite quail (Colinus virginianus) is a common threat during the late winter, spring, and early summer months. During this time of year, new mothers and young are most vulnerable6– a fact of life that predators rely on as a primary source of nutrition for their own young survival. Fawn and nest predation includes both mammalian and avian culprits, but avian predators are more difficult to manage from a regulatory aspect. Mammalian predators of frequent concern include, but are not limited to, coyotes (Canis latrans), raccoons (Procyon lotor), bobcats (Lynx rufus), grey foxes (Urocyon cinereoargenteus), hog-nosed skunks (Conepatus leuconotus), opossums (Didelphis virginiana), badgers (Taxidea taxus), feral hogs (Sus scrofa), nine-banded armadillos (Dasypus novemcinctus), feral cats (Felis catus), and feral dogs (Canis familiaris) 2,3,4,6. Although the effects of mammalian predator management on nesting success and survival is largely unknown, there has been evidence showing it results in significant improvements for fawn survival and recruitment3.
There are many methods for controlling predator population sizes, but snare trapping on fence-lines is a time- and cost-effective method that is often utilized for trapping mammalian predators like coyotes in southern Texas5. A snare is one of the oldest and most rudimentary traps, constructed from a simple wire or cable loop with a locking device that creates a cinch effect– as the animal pulls harder, the loop locks tighter and tighter around the animal’s body1,5. Snares can, however, be set for more species-specific captures, if desired, with cable stops (allows smaller animals to escape and larger animals to avoid leg catches) and trap set design (loop size, cable-size, trap placement location, etc.)1.
For snares to be most effective, it is recommended to trap on fence-lines constructed of net-wire5, which forces most predators underneath and creates a habitual travel route that is easily accessible and advantaged for trappers. Identifying fence-line travel paths with higher traffic allows property and/or wildlife managers to trap predators more efficiently and effectively. Filling in holes that traverse under net-wire fencing forces predators to re-dig or dig new holes under the fence; these new holes indicate recent and potentially frequently used areas and can be leveraged for snare trap sets. It is not known if different hole filling substrates (dirt, concrete, razor wire, cactus, thorny brush, etc.) are more effective than others at deterring predator re-digs, but reduced re-dig activity could concentrate the travel across fence-lines and increase the frequency of trapping success with less effort. This experiment sought to determine if different filler materials made a difference in fence-line hole re-dig activity.
The experiment was conducted over a 39-day period (2/2/2024–3/11/2024) on a 546-acre white-tailed deer ranch approximately 12 miles East from Dilley, Texas in La Salle County. The perimeter of the property is surrounded by an eight-foot-tall game-proof StaTite net-wire fence with two vehicle drive-through gates over cattle guards. There are no livestock on the ranch, but white-tailed deer are managed extensively for a hunting operation.
The ranch shape is an approximate rectangle with 3.8 miles of perimeter fencing. A total of 40 predator-made holes traversing the game proof fencing were identified and enrolled in the study; 16 holes on the southwestern fence (1.2 miles), two holes on the northwestern fence (0.7 miles), 15 holes on the northeastern fence (1.2 miles), and seven holes on the southeastern fence (0.7 miles). When a hole was discovered, notes were recorded about the hole to better estimate the primary culprit of the hole in question; these notes included measurement of the hole size (width and height), notes on the type and density of the surrounding vegetation, suspected culprits (based on tracks, scat, hair caught in the fence, etc.), and the estimated frequency of use based on trail wear. Holes were filled in with either dirt only (as a control), a mix of dirt and prickly-pear cactus (Opuntia basilaris platypuntia) paddles, or a mix of dirt and thorny brush clippings from honey mesquite (Prosopis glandulosa), blackbrush (Coleogyne ramosissima), and allthorne (Koeberlinia spinosa). The filler used for each hole was rotated so that the order was dirt–dirt/cactus–dirt/thorny brush–dirt–dirt/cactus–… so that holes were randomly filled and so there was an even number of samples distributed across the three test groups. Holes were checked after four-, 14-, and 23-days for re-dig activity. If a hole was re-dug, measurements and notes were recorded for the new hole and it was then re-filled with the next filler in the order from the previous filler (i.e. if the previous filling attempt was dirt only, the refill was with dirt/cactus). A successful re-dig was defined as a hole that traversed completely underneath the net-wire fence. Holes at the end of the experiment were used for future snare trap sites.
Results and Discussions
Predator holes under the fence had a size range of 7–32 inches wide (w) and 3.5–14 inches deep (h), with an average hole size of 15.9 inches (w) by 7.5 inches (h). The suspected culprits of holes, with occasional evidence on multiple suspects, included coyotes (n=34), javelina (Pecari tajacu; n=7), raccoons (n=5), armadillos (n=2), and bobcats (n=1). Re-dug holes (n=20) ranged in size from 4–22 inches (w) and 3–10 inches (h). The average size of a re-dug hole was 10.9 inches (w) by 6.4 inches (h). The suspected culprits of re-dig activity, with occasional evidence of multiple species at one re-dig site, were coyotes (n=15), bobcats (n=4), javelina (n=3), raccoons (n=2), and skunks (n=1). Vegetation type and the estimated frequency of use did not seem to predict re-dig activity. The hole size associated with each species determined by evidence is shown in Table 1. Although there is a high degree of overlap in hole dimensions between target species and non-target species (javelina), hole size and evidence used simultaneously can inform the trapper of the most likely species to travel the hole to reduce unintended bycatch. Selective snare setting or non-lethal snares (with cable stops) can also reduce non-target bycatch1, which can be a common occurrence with snares. Trap lines should be checked daily, if possible, to insure traps are properly and continuously set and that caught animals are not subjected to prolonged suffering or injuries, especially if using non-lethal snares.
Of the 40 predator-made holes identified and filled in the experiment, a total of 20 successful re-digs and four unsuccessful re-digs occurred. There was a total of 14 holes filled or refilled with only dirt, 18 holes filled or refilled with dirt/cactus, and 15 holes filled or refilled with dirt/thorny brush, and 13 holes remaining at the end of the experiment for snare sets. Dirt alone was the least successful deterrent for predator re-dig activity; of 9/14 (64%) dirt-filled holes experienced successful re-dig attempts and 0/14 (0%) unsuccessful re-dig attempts. Although dirt/cactus-filled holes experienced one more successful re-dig attempt than dirt/thorny brush-filled holes (6/18 versus 5/15), both groups experienced the same statistical occurrence of successful re-dig attempts (33% success rate). Dirt/thorny brush-filled holes did, however, experience a slightly higher rate of unsuccessful re-dig attempts (11%) than that of dirt/cactus filled holes (13%). Evidence indicates that the addition of any deterring substrate (cactus or thorny brush) to filled holes reduced the rate of re-dig activity by half. It should be noted that cactus added as a hole filler may promote cactus growth along fence-lines, which may inhibit fence maintenance but could, if thick enough, also act as a natural succulent fire break in a wildfire situation. There was new cactus growth in some holes by the end of the study (within 39 days). Less penetrable filler such as razor wire, galvanized steel panel, or concrete may further deter predator re-dig activity, but is more costly and time-consuming.
Table 1: Holes dimensions associated with evidence of various predators.
The dimensions listed are in inches. The average is shown with the range shown parenthetically as (minimum – maximum). There is a significant overlap in hole dimensions among common predators (coyotes, bobcats, raccoons) and non-target species (javelina). * Indicates no range is provided because there was only one sample.
Literature Cited
- Boddicker ML. 1982. Snares for predator control. Proceedings Tenth Vertebrate Pest Conference pp50–54.
- Dreibelbis JZ, Melton KB, Aguirre R, Collier BA, Hardin J, Silvy NJ, Peterson MJ. 2008. Predation of Rio Grande Wild Turkey Nests on the Edwards Plateau, Texas. The Wilson Journal of Ornithology 120(4):906–910.
- Guthery FS, Beasom SL. 1977. Responses of Game and Nongame Wildlife to Predator Control in South Texas. Journal of Range Management 30(6):404–409.
- Rollins DA, Carroll JP. 2001. Impacts Of Predation On Quail. The Role of Predator Control as a Tool in Game Management Proceedings of a Symposium pp84–101.
- Texas A&M AgriLife Extension Service–Wildlife Services. 2022. Managing Coyotes With Snares. Accessed July 9, 2024.
- Watine LN, Giuliano WM. 2017. Factors Determining Coyote (Canis latrans) Diets. Open Journal of Ecology 7:650–666.
