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Wildlife Damage Management and Invasive Species

The best method for dealing with invasive species is to prevent introductions. Although global traffic volume increases continuously, many nations have no invasive species policies. In the United States, no comprehensive law addresses imports of nonnative species, so regulatory agencies have often assumed a species will pose no problems unless proven otherwise.

It is more expensive to deal with introduced species once they are established than to prevent their introduction. Eradication is often the most cost-effective and ecologically sound solution, but can be difficult and sometimes controversial, and is most feasible in the early stages of invasion or on small islands. Rats have been eradicated using rodenticides on a number of areas, including the Aleutian Islands, Caribbean islands, and islands off of New Zealand. Eradication of goats has been successful on 37 islands (up to 46,000 ha) throughout the world, primarily in New Zealand, Australia, and the Galapagos.

Where eradication is impossible, invasive species can often be managed to reduce their economic and/or ecological damage. Hunting can limit populations of feral pigs, and feral goats. Exclusion by fencing is successful but expensive. Trapping is used successfully to manage some invasive species. Brown treesnakes are trapped around airfields and ports on Guam to prevent their dispersal to other islands. Trapping and snaring are used to reduce pig and goat populations in Hawaii and in the Great Smoky Mountains National Park in the southeastern United States.

Toxicants can provide a rapid initial reduction of invasive populations. Various rodenticides have been used effectively to manage rat populations throughout the world. Compound 1080 is used in Australia and New Zealand for controlling rabbit populations, in New Zealand for controlling brushtail possoms, and on Aleutian and Pribolof Islands for eradicating arctic fox. A variety of toxicants have been used to control pigs, deer and goats. Acetaminophen (a human pain relief medicine) is being used to control brown treesnakes on Guam, and caffeine sprays are being developed for controlling introduced frogs on Hawaii.

Research is being conducted on reproductive controls which could eventually reduce invasive species populations. Reproductive control will be most effective in managing species like rats with high reproductive and low survival rates, and least effective for species such as deer with low reproductive and high survival rates.