There may be situations in which the only practical solution to your prairie dog problem involves lethal methods. But lethal removal must always be considered as a last resort. It is important to remember that it is very likely that prairie dog predators are cohabitating with the prairie dogs. In choosing to poison or otherwise destroy the prairie dog, you will probably be killing other forms of wildlife, possibly including endangered species (9). That having been said, if lethal control is the only option, it is of utmost importance that the removal process involves careful planning, attention to the regulatory requirements, and commitment to safe and environmentally sound practices.
While the anti-hunting group might find shooting prairie dogs to be highly offensive, it is a very selective way of killing prairie dogs without targeting non-target wildlife (1,2). When I was conducting range management research on the Pine Ridge Indian Reservation in the late 70's, my students supplemented their meager incomes by shooting prairie dogs and collecting a 35-cent bounty for each tail. Today prairie dog hunts are big business. I recently saw one group promoting "trophy prairie dog" hunts. I'm just not sure how to tell a trophy prairie dog from the "run-of-the-mill" prairie dog. While prairie dog hunting may provide good "sport" for some people, it is often of limited use in controlling the prairie dog population. Continuous shooting can remove 65% of the rodents in a given year (1,2). Hunting can help slow colony expansion where needed (3), but it doesn't usually prove to be cost effective for major control issues. Also, prairie dogs quickly become gun-shy. They are typically hunted with .22s or slightly larger caliber and shot from long distances using tripod, portable shooting benches, telescopic sights, and spotting scopes (1,2).
One type of toxicant is the toxic bait, which is applied as a grain to be eaten by the prairie dog. The only toxic baits that are approved for prairie dog control are 2% zinc phosphide treated grain bait and pellet formulations (1). Only certified pesticide applicators are authorized to use this toxicant (1, 2, 3). It is much more toxic to rodents than it is to carnivores (3). Toxic baits work best when the prairie dogs are active, but where there is no vegetation available. For this reason they are best applied late summer and through the fall. Zinc phosphide must only be used from July until January 31 (1) (December 31 in Colorado (3)). Be certain to check state regulations before applying zinc phosphide.
It is important to prebait areas in which zinc phosphate bait will be used. Prairie dogs must have time to adjust to eating a different food. This can be done by dropping a heaping teaspoon of rolled oats (if that is the bait that will eventually contain the zinc phosphide) on a bare area at the edge of the mound. Do not apply it inside of the burrow, on top of mounds, near prairie dog droppings, or in vegetation that is not close to the prairie dog mound (1). Once the prairie dogs are readily consuming the pre-bait, the toxic bait may be applied. Use one teaspoon per mound, as was done with the prebait. It is important to wear rubber gloves when handling zinc phosphide. Contact your local extension agent or the USDA-APHIS-ADC if needed. Do not apply pre-bait or zinc phosphide on wet, cold, or windy days. Toxic baits have success rates of 75% to 85%. If higher rate of control is required, toxic bait can be followed up with a fumigant.
Zinc phosphide usually poses little threat to non-target species. Rabbits, seed eating birds, waterfowl and pheasants have been victims of misuse of zinc phosphide when application rates were much higher than label recommendation (3). It is best to remove livestock from area before treating with zinc phosphide, but is is not absolutely necessary. After treatment, clean up any uneaten zinc phosphide bate so that it cannot be eaten by a non-target species (5).
The most commonly used fumigants are aluminum phosphide tablets and gas cartridges (1). However, fumigants are not generally recommended for large numbers of prairie dogs. They are 5 - 10 times more expensive to apply, and tend to be more hazardous to non-target species and humans than toxic bating techniques (1,2,5). Fumigants are generally used as a follow-up after toxic bating. Best results are obtained when the soil is moist and the temperature is greater than 60 F. If applied correctly, 85% to 95% success rates can be expected when fumigants are used as follow-up treatments (1,5). It is very important to check for signs of non-target species, particularly endangered species before applying fumigants, as it is illegal to use fumigants when endangered species such as black footed ferrets are present (5,8).
Aluminum Phosphide: Aluminum phosphide is a Restricted Use Pesticide (6). It is registered as a fumigant for the control of burrowing rodents and must be applied by a licensed applicator. It is also flammable, and when used commercially must be transported in compliance with the Department of Transportation. Aluminum phosphide emits phosphine (hydrogen phosphide) when exposed to moisture in the soil (2,7, 9). Phosphine gas is absorbed through the respiratory passages of the prairie dog. It enters the bloodstream and blocks physiological processes in cells and alters hemoglobin (2.3).
Gas Cartridges: Individuals need not be certified to use gas cartridges. These cartridges contain sodium nitrate and charcoal. It is ignited and then placed in the burrow, and the burrow is sealed. Since sodium nitrate is an oxidizer, it continues to produce oxygen in the sealed burrow, and the charcoal continues to burn. Carbon monoxide produced in the reaction results in suffocation of the prairie dog. Moisture in the soil is necessary for good results. Gas cartridges are considered to be a humane means of euthanasia (2,3). Gas cartridges are fairly easy to use. One need only punch five or six holes in one end of the cartridge with a nail or ice pick, push the sharp point part way into the burrow and rotate the cartridge to loosen the contents. This will facilitate burning. The fuse can then be inserted and lit. Once it is burning well, it can be rolled into the burrow as far as possible. The opening is then plugged with soil or sod (grass sod down) to form an air tight seal (4).
Acrolein: Acrolein is a very volatile liquid that causes lacrimation (tearing of the eyes) and respiratory failure (3). As with the other fumigants, Acrolein is very effective (90%) against ground squirrels , but only 55% effective against prairie dogs (3). Check with your state for licensing requirements.
Rodenator: One of the latest prairie dog and gopher controls to "explode" onto the market is the rodenator. This device not only kills the prairie dogs, but also flattens their tunnels. This helps to prevent injuries to horses and human athletes, and removes the blemishes to the land left by prairie dog colonies. Oxygen is mixed with propane and injected into the prairie dog burrows. Propane is heavier than air, so the mix sinks into the tunnels and dens. It is ignited and produces an expanding force that reportedly travels 5,000 feet per second. The concussion flattens the tunnels and kills 90% of the prairie dogs. The remaining animals can be trapped and removed from the area. Many people view this technique as "the most inhumane technique of all." The benefits, however, are that there is no poisonous residue remaining to threaten the environment or health of humans (10, 11).
There are many alternatives to lethal removal of prairie dogs. One alternative, being proactive, is often the least used, and sometimes the most successful technique of all. If the rangeland is managed properly from the start, and not over farmed or over grazed, the prairie dogs are not as likely to take over. In the last article of this series we will discuss prairie dogs as a keystone species, and the pros and cons of restoration ecology on the prairie.
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