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Chemical Repellents

Toxicants

Most current chemical repellents used in wildlife damage management are area repellents or contact repellents. These products are aimed primarily at birds and herbivores such as deer (Conover 2000).

Area repellents work by producing odors that are disagreeable or frightening to the damaging species. Some examples of area repellents are moth balls, and bars of soap hanging from trees. Predator (coyote, fox, etc.) urines have unique odors (sulfers), detectable by other animals, and frightening to them. The main fault with area repellents is that animals lose their ability to detect an odor after repeated exposure (Conover 2000).

Contact repellents are applied directly to food items and ingested with the food. These repellents either cause illness when consumed (aversive conditioning) or give the food an objectionable odor or taste. Primary repellents are painful or irritating upon contact and causes a mammal or bird to respond reflexively. Secondary repellents are not disagreeable (aversive) immediately but produce illness or discomfort sometime after they are eaten. The effectiveness of these compounds is based on the concept of conditioning an animal to avoid the food. Contact repellents wear off or decompose fairly rapidly and applying substances to rapidly growing plants is difficult.

Numerous odor and taste repellents have been developed for deer, including blood meal, hot sauce (capsaicin), thiram, and, the most effective compound, Big Game Repellent BGR®. No repellent has reduced browsing damage by more than 50% and more study is needed in this area (Conover 2000).

Recently, casein (an animal protein precipitated from milk) has been evaluated as a repellent to minimize deer damage to trees and shrubs. Retail sources of hydrolyzed casein (HC) (concentrated baby milk powders) are not as effective as pure hydrolyzed casein but do offer some protection. The product can be used in nurseries, orchards, and in reforestation projects. For the homeowner, a simple repellent formulated with glue and an HC-containing baby formula may be effective when alternative forage is available (Kimball et al. 2005)

Bird repellents essentially move birds from one place to the next. After successful application of a bird repellent, the overall amount of damage will probably not decrease, but it will be distributed differently.

Recent studies have looked at common products such as caffeine for repellent properties. One approach to managing blackbird damage is the application of caffeine to protect rice. Cage feeding trials with female red-winged blackbirds and male brown-headed cowbirds confirmed that a treatment rate of 2500 ppm caffeine on rice seed reduced consumption as much as 76%. Trials with mixed species blackbird flocks in a 0.2-ha flight pen resulted in just 4% loss of caffeine-treated rice compared to 43% loss of untreated rice. Field trials of a 10,000 ppm caffeine treatment in Louisiana revealed >90% of caffeine-treated rice seed remained unconsumed on days 2 and 3 of the study whereas blackbirds consumed >80% of the untreated seed. As a rice seed treatment to deter blackbirds, caffeine appears to be effective, economical and environmentally safe, although additional aquatic toxicity testing is desirable. Improvements in formulation will be needed to make the compound practical for general agricultural spray applications and to extend the adherence of caffeine to rice seeds in field conditions (from Avery et al. 2005).

Currently, crop damage reduction with chemical repellents is limited to a few registered products:

• Methyl anthranilate

  (MA) is a naturally occurring compound that is used extensively in the food industry to impart grape or fruity flavor to candy, gum, soft drinks, and other consumables. . All avian species tested so far perceive MA as an irritant. In the United States, MA is the active ingredient in products marketed under the trade names of Bird Shield® and Rejex-it®. These products are registered as bird repellents for use on cherries, blueberries, grapes, corn and sunflower. In addition, other formulations are registered for use on turf and water to control geese and other grazing birds.

• Anthraquinone

  Anthraquinone under the brand name Flight Control® (http://www.flightcontrol.com) is registered as a treatment to repel birds from turf and grass, and also as a repellent for roosting birds. Anthraquinone is a secondary repellent.

• Methiocarb

  Methiocarb was originally developed by Bayer as an insecticide but repellent properties of the compound were quickly recognized. Birds that feed on methiocarb-treated food exhibit no sign that the chemical tastes bad, rather methiocarb is a secondary repellent-birds that feed on treated food become sick and associate either the food itself or characteristics of the food with the discomfort

• Avitrol®

  

  Avitrol® (4-aminopyridine) is considered by some to be a "behavioral repellent." It is highly toxic to birds and mammals. In the United States, there are several registrations for the control of blackbirds, pigeons, and various other bird species. Avitrol repels birds by poisoning some members of the feeding flock, causing them to become agitated and hyperactive. The distress calls emitted by the fatally poisoned birds frighten the other members of the flock so that they leave the area. Presumably after one such experience, the birds do not return to the site.

• Fungicides

  Although not designed to be used as bird repellents, a number of fungicides have been shown to reduce feeding activity of various bird species, including thiram, ziram, and copper.

• Other compounds

  Several substances that have offensive properties to humans are marketed as bird repellents. RoPel® is marketed as a repellent for geese, ducks, and woodpeckers on lawns and around structures. The active ingredients are denatonium saccharide and thymol, neither of which is offensive to birds. Bye-Bye Birdie® is sold as a repellent to deter starlings, pigeons, sparrows and other birds from structures. It contains 100% naphthalene, which has been shown to be inoffensive to birds. There is a persistent impression that capsaicin, the active principle in hot capsicum peppers, is an effective bird repellent. However, it is well-documented that birds are insensitive to capsaicin. There are fundamental differences between the avian and mammalian chemosensory worlds, and just because a compound is irritating or offensive to mammals does not mean that birds will respond the same way. There is evidence that derivatives of the neem plant (Azadirachta indica) have bird-repellent properties because of the compound a adirachtin.

The above summary on bird repellents comes from Avery (2002). See this article for an in-depth discussion.

Literature Cited and References

AVERY, M. L. 2002. Avian repellents. Pages 122-128 in J. R. Plimmer, editor. Encyclopedia of agrochemicals. Volume 1. John Wiley & Sons, Hoboken, New Jersey, USA.
http://www.aphis.usda.gov/ws/nwrc/is/02pubs/aver027.pdf

AVERY, M. L., S. J. WERNER, J. L. CUMMINGS, J. S. HUMPHREY, M. P. MILLESON, J. C. CARLSON, T. M. PRIMUS, AND M. J. GOODALL. 2005. Caffeine for reducing bird damage to newly seeded rice. Crop Protection 24:651-657.

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

05-51 KIMBALL, B. A., D. L. NOLTE, AND K. B. PERRY. 2005. Hydrolyzed casein reduces browsing of trees and shrubs by white-tailed deer. HortScience 40:1810-1814. 244K