Individual study: Evaluation of propane exploders as white-tailed deer Odocoileus virginianus deterrents at the NASA Plum Brook Station, Ohio, USA
Belant J.L., Seamans T.W. & Dwyer C.P. (1996) Evaluation of propane exploders as white-tailed deer deterrents. Crop Protection, 15, 575-578
White-tailed deer Odocoileus virginianus populations in the USA have increased greatly in recent years and this species is most often implicated in causing agricultural crop damage in eastern USA. Airports frequently contain large expanses of grassland which are attractive to deer, with associated safety concerns (deer responsible for 65% of aircraft-mammal collisions in USA). In response to increased white-tailed deer damage to crops and encroachment on airports, as an alternative to shooting, the effectiveness of systematic and motion-activated propane exploders as deterrents were tested. Systematic exploders detonate at standard or random time intervals but fire regardless of whether an animal is nearby. Motion-activated exploders detonate only when animals approach, habituation is therefore thought to occur less rapidly.
Study site: Trials were conducted during 1994-1995 in the 2,000 ha National Aeronautic and Space Administration Plum Brook Station (PBS), northern Ohio. PBS is enclosed by a 2.4 m chain-link fence and had an estimated white-tailed deer population of 2,000 (91 deer/km²) over the experimental period. Habitats consist mostly of grassland and hardwood forest.
Feeding stations and pretreatment: Six feeding stations at least 1 km apart were established in grassIands. These comprised 100 m of 1.5 m high plastic fence erected in a semi-circle. In each, 23 kg of corn Zea mays was placed in a 1 m circle at the centre of the arc, 2-4 m in from the fence. The fence allowed deer access from one direction only. A non-functioning exploder ('Scare Away cannon') was placed at each station 3-5 m from the bait on the opposite side of the fence. An automatic counter was placed to record deer entering or leaving. To condition deer to using the feeding sites, one month prior to each trial period, feed was put out and no exploders were fired. The number of intrusions was recorded and corn replenished as needed.
Trials: Three trials were conducted: Trial 1, 9 August-12 September 1994 (late summer); Trial 2, 20 September-24 October 1994 (autumn); and Trial 3, 27 April-12 July 1995 (spring/early summer). Experiments were discontinued when it was determined that the exploders had been ineffective for 22 weeks. To reduce potential for habituation, treatments were alternated among the same three feeding sites between Trials 1 and 2; the three remaining stations were used during Trial 3.
During each trial, three stations were assigned randomly to one each of three treatments: a systematic, motion-activated, or non-functioning (control) exploder. Systematic exploders detonated once every 8-10 min, irrespective of deer presence. Motion-activated exploders detonated eight times in 2 min (1 detonation/l5 s) about 10 s after a deer was detected. At each station, the daily number of deer intrusions was recorded.
Trial 1: The motion-activated exploder reduced the average number of intrusions by 63% during week 1 (from a pretreatment level of 251 to 94). However, intrusions during week 2 (239) were comparable to pretreatment intrusion rates.
Compared with daily pretreatment intrusions (183), deer intrusions at the systematic exploder were greater during weeks 1-2 (346). However, the average number of intrusions during days 1-2 (94) was 54% less than that during pretreatment (206). Intrusions declined during week 3 (230) but remained higher than pretreatment levels. Variation at the control site was due primarily to high intrusion rates during week 1 pretreatment (617) and week 2 post-treatment (556).
On average, the motion-activated exploder detonated 11.6 times more often (1,856 times/day) than the systematic exploder.
Trial 2: The number of deer intrusions at the control and motion-activated exploder sites differed among weeks. Variation in intrusions at the control was due primarily to 27 and 41% decreases occurring during week 2 pretreatment and week 3 post-treatment, respectively. The motion-activated exploder did not reduce the number of intrusions. This effect was a consequence of an unexplained 55% reduction in intrusions occurring between weeks 1-2 pretreatment. Average daily intrusions at the systematic exploder site during pretreatment and post-treatment were similar. However, the average number of intrusions at the systematic exploder during days 1-2 (114) was 44% less than the average during pretreatment (202). In contrast, the average number of intrusions during days 1-2 (191) at the motion-activated exploder decreased by only 5% from an average of 200/day during pretreatment.
On average, the motion-activated exploder detonated 13.8 times more often (2,200 times/day) than the systematic exploder.
Trial 3: The motion-activated exploder reduced daily average intrusions by 80% for six weeks relative to pretreatment levels (168 to 34). In contrast, intrusions at the systematic exploder site during weeks 1-4 generally remained as pretreatment levels, then increased and stabilized during weeks 5-9. Although the systematic exploder was ineffective overall, the average number of intrusions during days 1-2 (132) was 53% less than that during pretreatment (279). The number of intrusions at the control site was similar among weeks.
On average, the motion-activated exploder detonated 4.2 times more often (675 times/day) than the systematic exploder.
Conclusions: Due to detonation predictability, it is considered that habituation occurred more rapidly at systematic exploder sites compared to motion-activated exploder sites. Reducing the firing rate of motion-activated exploders might produce a similar deterrent effect to that acheived here, whilst reducing operating costs. There was great variability in deer use at specific feeding sites which makes data interpretation problematic. Motion-activated exploders appear more likely than systematic exploders to reduce deer damage over several weeks. Systematic exploders, however, may be effective in the short-term (a few days).
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