NestWatch | Dealing with Predators

What to do about Predators

Although nest boxes provide nesting opportunities for many native birds, they also can make easy targets for predators. Common predators of nests in nest boxes include raccoons, cats, snakes, and squirrels. Here are some tips to help you thwart these common nest box predators.

The most passive way to prevent predation is to avoid placing nest boxes in areas where predators are prevalent. But, because some predators are prevalent everywhere, you should consider protecting your nest boxes with predator guards. Recent research using NestWatch data suggests that, on average, nests in boxes with predator guards had success rates 6.7% higher than nests in boxes without guards. And while all types of guards were correlated with improved nesting success, birds nesting in boxes with cone-type baffles, stovepipe baffles, or entrance hole extenders (also called “wooden block hole guards”) were most likely to result in successful nesting (Bailey and Bonter 2017).

Raccoons and Domestic Cats

Raccoons and cats are abundant in both rural and suburban areas. Raccoons are especially difficult to deter because they are very intelligent. Once they learn that nest boxes are good sources of food, these nocturnal creatures have been known to destroy nests in entire groups of boxes. Similarly, cats can quickly learn that nest boxes can be the source of an easy meal. When raiding nest boxes, both raccoons and cats will leap to the top of a box, sit on the roof, and “dip” into the entrance hole with their front paws to grab the eggs or young birds inside.

Ways to prevent raccoons and cats from raiding your boxes:

• Installing a roof that extends five inches beyond the front of the box will prevent these animals from easily reaching into the entrance hole from above.
• Mount your box high enough and away from trees so cats cannot spring to the top of the box in a single leap.
• Attach predator guards to your boxes to prevent these animals from climbing up from below. Three commonly used guards are shown below.
• Keep pet cats indoors.
• Do not feed feral cats. This will encourage them to stay in the area.
• Avoid leaving out pet food or bird seed that can attract predators to an area.

Snakes

Snakes are an occasional predator of eggs and nestlings, especially in southern states. A conical metal collar mounted below the box will prevent most snakes from climbing up from below, but very large snakes can occasionally circumvent these barriers. In this case, it is helpful to have a Noel predator guard installed as a backup. Pole-mounted nest boxes should be placed away from trees to prevent snakes from accessing them from overhead branches. If your box is mounted to a tree or utility pole, you can use an acetate sheet wrapped around the trunk to prevent snakes.

Squirrels

In some regions, squirrels do great damage to nest boxes. By chewing at entrance holes to enlarge them, they make it easier for themselves and other predators to enter. If squirrels are common in your area, simply cut a hole the same size as the nest box entrance hole in a rectangular piece of sheet metal and attach it to the front of the nest box so that both holes line up.

Fire Ants

Fire ants, common in the Southeast, can be attracted to active nests. To prevent them, add a baffle (see below) to your freestanding pole. Then, caulk the area between the baffle and the pole to prevent the ants from getting in between them and add petroleum jelly to the pole just below the caulk. The baffle keeps the petroleum jelly from washing away in the rain and the petroleum jelly prevents the ants from getting a good grip on the pole. If you don’t have a box on a freestanding pole (like on the side of a house or on a tree), you might not be able to fully prevent the ants from accessing the box. If you decide to move the nest box, make sure you wait until breeding season is over.

A Note About Predator Removal

It’s important to remember that native predators can also benefit birds; for example, a ratsnake may consume only a few birds’ nests a year but will also consume many more rodents, which play a large role in nest predation. Some birds even selectively nest near predators because it affords them some protection against other smaller predators (this is called a protective nesting association). Additionally, state laws typically protect native mammals and snakes, and permits are needed to cull them (translocating wildlife is generally not recommended due to the risk of spreading disease).

Plans for Predator Guards

Stovepipe baffle
This device is made from a piece of stovepipe or PVC pipe that encircles the nest-box pole. It is held in place by hardware cloth and straps.

Noel predator guard
The Noel guard is a rectangular tube of hardware cloth stapled to the front of the nest box. This will make it difficult for predators to reach into the box entrance hole; however, the nest-box occupants can easily come and go.

Conical metal predator guard or collar
This guard works well for boxes that are attached to free-standing poles. The collar is a made from a circular piece of galvanized sheet metal that is placed around the pole underneath the nest box.