Author: Lynn Braband, NYS IPM Program of Cornell University
Tree-dwelling squirrels are among the most familiar, enjoyable, yet frustrating wild animals in our immediate surroundings. While adding a touch of nature to even the most urban environments, they can be a headache to gardeners, rob bird feeders, and damage buildings. They can cause power outages by climbing into electrical transformers and substations.
There are several species of tree squirrels in North America, and the particular mix varies from region to region. Nationwide, they include the gray squirrel (Scirus carolinensis), fox squirrel (S. niger), red squirrel (Tamiascirus hudsonicus), and flying squirrels (Glaucomys sabrinus and G. volans). While there are important behavioral differences among these species that affect their management, I will discuss a general framework for controlling squirrel problems in buildings.
The laws regarding squirrel removal vary from state to state. For example, in New York State, where I live, gray and fox squirrels are classified as protected game animals, while red and flying squirrels are unprotected. Check with the local office of your state wildlife agency for the important details.
As with all pests, preventing problems before they occur is preferable to reacting to a well-established headache. For squirrels, this includes regular inspections of building exteriors, especially if the structure has a history of problems. In much of the nation, important times for inspections are in the late winter/early spring (females seeking sites for raising young) and early- to mid-fall (squirrels setting up winter dens). Since tree squirrels are climbing animals, such inspections usually need to be done with a ladder since all possible entry sites can rarely be seen from the ground. If practical, reduce squirrel access to the building by keeping trees and tree branches at least 10 feet away from the structure and make sure all vents are made of animal-resistant materials.
If a possible entry hole is found, do not close the opening without first determining if it is active. An animal seeking to get out or chew it’s way back in can cause additional damage. Monitor the opening by sticking a “soft plug,” such as newspaper, in the hole. Tree squirrels do not hibernate and will remain active even in very cold weather. If the plug has not been disturbed for at least two days and there are no other signs of activity inside the structure, it is usually safe to close the hole. When doing squirrel exclusion, think “metal.”
If squirrels need to be removed from the building, your state’s wildlife regulations will prescribe the boundaries for the techniques and circumstances permitted. There are no rodenticides or other poisons legally registered for tree squirrel control in buildings. Although a variety of repellents and devices make marketing claims about driving squirrels from buildings, their efficacy is very questionable. The most common successful method of squirrel removal is by trapping. Both live traps and lethal devices are available. Another method is using one-way doors (also known as excluders) installed over the entry holes. These devices allow animals to leave but not re-enter the structure. To be successful, one-way doors often need to be combined with preventative exclusion on other vulnerable sites on the building.
For more details, consult the NYS IPM Program publication, Beasts Begone http://www.nysipm.cornell.edu/publications/beasts/default.asp and/or visit the Internet Center for Wildlife Damage Management http://icwdm.org/ .