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Alternative Nonlethal Control Methods

Habitat Manipulation | Alternate Foods |
Barriers | Translocation | Guard Animals

Habitat Manipulation

Habitat manipulation or cultural modifications can be used to make sites or crops less attractive to mammals and birds. For example, removal of nesting cover can reduce blackbird damage to crops and improve habitat for waterfowl (Dolbeer 1999). Each summer, millions of blackbirds congregate in cattail marshes in Minnesota and the Dakotas. From these marshes the birds fly to nearby fields to feed on sunflower seeds, causing significant damage. Wildlife managers are increasingly using the herbicide glyphosate (Rodeo®) to reduce cattail habitat, which in turn reduces blackbird concentrations and associated damage to sunflower fields. Thinning the marsh vegetation results in an opening up of the marshes. This, in turn, provides more waterfowl breeding habitat.

Habitat manipulation can also decrease the risks of livestock depredation (e.g. removal of invasive species of trees such as tamarisk can remove cover for predators [Mason 2002]). A variety of silvicultural practices can be pursued. Thinning tree stands can make a habitat less attractive. It's been shown that pine vole damage in orchards may be reduced by mowing 3 times a year, clearing vegetation from under trees, and removing pruned branches. In the Pacific Northwest, tree plantation managers can plant species less susceptible to rodent or browsing damage such as Sitka spruce, western hemlock. In fields, insect control can make it less attractive to hungry birds (Dolbeer 1999).

Bird resistant cultivars of corn, sunflower and sorghum have been effective in reducing damage. For example, ears of corn with long thick husks are more difficult for blackbirds to penetrate. Early maturing cultivars of cherries may be more susceptible to damage than late-maturing cultivars.

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Alternate/Supplementary/Diversionary Foods

The use of lure crops (food intentionally placed in a nearby area to draw or "lure" depredating species away from a crop) can reduce damage to nearby commercial fields where bird-frightening programs are in place (Dolbeer 1999). Provision of alternative foods (e.g. grains scattered on the ground) may reduce loss of corn seedlings to rodents in fields and damage to apple trees in winter.

For example, in an effort to reduce blackbird damage to commercial sunflower, which can range from $4-11 million annually in North Dakota and South Dakota, scientists evaluated Wildlife Conservation Sunflower Plots (WCSP) for efficacy and wildlife benefits. Blackbird depredation has caused some producers to reduce sunflower acreages and seek alternative crops in this optimal sunflower growing region. USDA's Wildlife Services funded 8-ha units of oil sunflower (WCSP) to lure migrating blackbirds away from commercial sunflower fields. Vegetative data, habitat variables, GIS-analyzed land-use data, weekly blackbird surveys, sunflower damage surveys, and avian point counts will be used to evaluate the effectiveness of the WCSP. Preliminary analysis of the 2004 field data showed that blackbird and nonblackbird density is significantly greater in WCSP than in commercial sunflower. Habitat variables and spatial landscape features are currently being reviewed in order to account for the difference. Under so me conditions, trees and wetlands are significantly correlated with blackbird damage and abundance in sunflower. We further hypothesize that proximity to shelter belts, wetlands, cattail stands, other grain crops, and/or large commercial sunflower acreages influences avian use of WCSP (Hagy et al. 2005b).

In the Pacific Northwest, supplemental feeding is a key element in reducing black bear damage to trees in industrial timber stands. Containers of food remain out from spring through early summer. This damage prevention method is costly but effective. In addition, there is no evidence that attracting bears to feeders increases populations, increases fighting among adults, or increases aggression by male adults against cubs. Supplemental feeding can also be a useful component of integrated strategies to manage black bear depredation on livestock (Mason 2002). A caveat -supplemental feeding is more useful in some setting than others and with some predators than others (Mason 2002).

Another way to reduce damage in forests and plantations is to enhance alternative food sources-such as trailing blackberry, hawkweed, and red huckleberry, where these species do not compete with seedling growth. This can lower browsing damage by deer, elk and moose.

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Barriers

Barriers to keep animals from areas, plants or structures continue to be investigated. Barriers can be more practical and less costly than other methods in a variety of situations.. Electroshock techniques, applied in water, are also being developed to change the activity patterns of aquatic birds and mammals around protected areas. Plastic netting can exclude birds from individual fruit trees or high-value crops such as blueberries or grapes. Wire grids can protect fish ponds from bird predation.

There are many different fence designs for excluding animals such as deer and elk from crop areas. Deer, motivated by hunger or fear, can overcome an electric fence or a 3-m-high chain-link fence, but under test conditions, one of the electric fencing products, ElectroBraid, reduced deer penetrations 88-99% (Seamans and Vercauteren 2006). In addition, the fence could be set up, taken down, and moved relatively easily. Complete elimination of deer penetrations was never achieved. The motivation for deer to penetrate perimeter fences should be minimized, which will enhance the efficacy of a fence. Also, increased power to the fence will make contact with the fence more painful and possibly increase the effectiveness of the fence.

Wire netting and electrified netting fences have excluded rabbits from crop fields (Dolbeer 1999.) Barriers to protect individual plants, particularly in forest industry applications, are generating new interest. For example, individual seedling protectors made of photodegradable plastics (e.g. VEXAR tubes) are effective in reducing ungulate and rodent damage to young conifer trees. In orchards, rabbit and aboveground rodent damage can be eliminated by wrapping trees with hardware cloth or burlap that is buried 10 cm deep around the tree base (Dolbeer 1999).

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Translocation

Translocation is the transporting of live-trapped animals to another location and releasing them. It's especially useful in reducing animal populations in specific areas. For example, it's been used to manage bears at garbage dumps or campgrounds. Translocation has also been used to remove deer from urban and suburban areas, and other locations where hunting is clearly not an option. Nuisance wildlife control officers also use translocation extensively to control urban and suburban wildlife problems such as those caused by raccoons and skunks, primarily because most customers do not want the animals harmed. Another place where animals have been captured and relocated is at airports where large raptors like hawks pose a threat to aircraft.

Effectiveness of translocation is rarely monitored and the fate of most animals is unknown. Essentially, translocation of problem animals makes sense only when (1) the animal is so valuable that it should be kept alive, (2) the population at the release site is below carrying capacity or, (3) when public relations are more important than other factors, i.e. moving live-captured animals is socially acceptable (Conover 2002).

Problems with translocation include: some animals have a strong homing instincts and will return home; animals that initially survive may starve or be unable to find shelter in unfamiliar areas; new animals may be competing with local animals; diseases and parasites can be transmitted; new animals may replace the ones relocated; and translocated animals may cause the same problems in their new surroundings as they did in the old (Conover 2002).

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Guard Animals

Guard dogs (and guard llamas and donkeys) have been used to limit livestock predation. However, not only are trained guard dogs expensive, they are also subject to early death and injury. Additionally, guard dogs have been known to turn on the animals they are supposed to protect or to stop chasing predators after a time, when they realize they won't catch the animals. Whether a guard animal is cost effective depends on such factors as the annual rate of predation, the ability and longevity of the animal, and the costs to purchase and maintain it (Conover 2002).

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Nonlethal Predator Control

Althering Human Behavior
Altering Predator Behavior

Literature Cited and References

CONOVER, M. R. 2002. Resolving human-wildife conflicts: the science of wildlife damage management. Lewis Publishers, Boca Raton, Florida, USA.

COPPINGER, L., AND R. COPPINGER. 1982. Livestock-guarding dogs that wear sheep's clothing. Smithsonian 13(1):64-73

DOLBEER, R. A. 1999. Overview and management of vertebrate pests. Pages 663-691 in J. R. Ruberson, editor. Handbook of pest management, Marcel Dekker, New York, USA.

FRANKLIN, W. L., AND POWELL, K. J. 1994. Guard llamas: a part of itegrated sheep protection. Iowa State University Cooperative Extension Pm-1527.

GREEN, J.S., AND R. A. WOODRUFF. 1990. Livestock guarding dogs: protecting sheep from predators. USDA/APHIS Animal Damage Control Agriculture Informatin Bulletin Number 588.

HAGY, H., G. M. LINZ, AND W. J. BLEIER. 2005a. Avian use of commercial sunflower and grain crops compared to USDA wildlife conservation sunflower plots in North Dakota. Sunflower Research Forum Papers 2005. National Sunflower Association,

HAGY, H., J. RAETZMAN, G. LINZ, AND W. BLEIER. 2005b. Decoy cropping methods for luring blackbirds away from commercial sunflower: USDA wildlife conservation sunflower plots. Proceedings of the Wildlife Damage Management Conference 11:304-310.

MASON, J. R., AND M. J. BODENCHUK. 2002. Depredation management outside the box: logical adaptations of successful practices with other species and situations. Proceedings of the Vertebrate Pest Conference 20:219-222.

MEADOWS, L. E., AND F. F. KNOWLTON. 2000. Efficacy of guard llamas to reduce canine predation on domestic sheep. Wildlife Society Bulletin 28:614-622.

RAETZMAN, J., G. M. LINZ, AND W. J. BLEIER. 2006. Blackbird use and damage of wildlife conservation sunflower plots: the second year. Sunflower Research Forum Papers http://www.sunflowernsa.com/research/research-workshop/documents/Raetzman_Blackbird_2yr_06.pdf.

SEAMANS, T. W., AND K. C. VERCAUTEREN. 2006. Evaluation of ElectroBraid fencing as a white-tailed deer barrier. Wildlife Society Bulletin 34:8-15.

VERCAUTEREN, K. C., M. J. LAVELLE, AND S. HYGNSTROM. 2006. Fences and deer-damage management: a review of designs and efficacy. Wildlife Society Bulletin 34:191-200.

VERCAUTEREN, K. C., M. J. LAVELLE, AND S. HYGNSTROM. 2006. A simulation model for determining cost-effectiveness of fences for reducing deer damage. Wildlife Society Bulletin 34:16-22.

05-88 VERCAUTEREN, K., G. PHILLIPS, R. POOLER, AND M. LAVELLE. 2005. Evaluation of livestock protection dogs for deterring deer from contacting cattle. Proceedings of the Wildlife Damage Management Conference 11:134.

05-89 VERCAUTEREN, K., N. SEWARD, D. HIRCHERT, M. JONES, AND S. BECKERMAN. 2005. Dogs for reducing wildlife damage to organic crops: a case study. Proceedings of the Wildlife Damage Management Conference 11:286-293.

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