Invasive predators are critical threats to many birds, but aren't these predators part of nature too? Understanding what makes a predator invasive is the first step toward minimizing the dangerous threat these animals pose to birds.

Defining Invasive

Not all predators are invasive, and an area's natural predators are a vital part of the local ecosystem. They cull sick, old or weak birds and other creatures to help keep overall populations strong and healthy, and do so in a delicate balance with other native wildlife, including their prey.

But an invasive predator is not natural to the area and is actually causing damage to the ecosystem. Also called exotic or introduced animals, invasive species can harm birds in a number of ways, such as:

• Directly preying on birds, eggs or chicks that have no defense or experience with a new type of predator.
• Destroying habitat by damaging plants, uprooting turf or changing soil or water chemistry.
• Taking over nesting sites for their own reproduction or as shelter sites.
• Usurping food supplies, thereby diminishing the amount of food available to native birds.
• Carrying diseases that can be contracted by birds or animals the birds depend on as prey.

Birds may be adaptable, but the changes brought about by invasive predators are swift and devastating. Even a robust species can have trouble adapting to the multiple threats one of these predators can introduce, causing drastic declines in bird populations.

How Predators Become Invasive

Not every predator, even every predator that is not native to an area, is automatically invasive.

The key is that the predator is adaptable to the new region where it is introduced, and it can reproduce so quickly and successfully that its population becomes overwhelming to native birds and other wildlife. There are several ways a new predator can be introduced, including:

• Escaped or deliberately released pets or domesticated animals that are able to reproduce and establish feral populations.
• Accidentally imported predators, such as rodents that arrive in new territories via ships.
• Deliberately imported predators that are released for one purpose, such as expected agricultural benefits, without adequate study of the consequences of their release on other native wildlife.
• Natural population shifts that allow a predator to expand into a new area, such as when a larger animal or other factor that kept the invasive predator in check is suddenly removed.

Common Invasive Predators

There are many animals that can be considered invasive predators, but each one is not an equal threat everywhere. Just how debilitating a predator can be depends on how widespread its introduction is, how fast its population grows and how drastically it affects native birds and wildlife. Some of the most widespread and most damaging invasive predators include:

• Cats
• Ferrets
• Mongooses
• Pigs
• Rabbits
• Rats
• Snakes

How You Can Help

Unfortunately, once an invasive predator has a thriving, established population, it can be very difficult, though not impossible, to remove. There are steps every birder can take, however, to reduce the threat these unwelcome predators pose to birds.

• Learn what animals are considered invasive in your area and what legal means can be used for their removal, such as trapping, hunting or contacting wildlife officials to report sightings.
• Support animal shelters that will take in exotic pets such as rats, snakes, rabbits and pigs so pet owners have no need to abandon their pets in the wild – which can lead to an invasive population – if they are no longer able to care for them responsibly.
• Never release your own pets or allow them to roam outdoors unsupervised; even if they are not completely part of the wild population, they can still harm wildlife and augment invasive predators, such as a pet cat breeding with a feral cat.
• Spay or neuter or your pets and support local programs that offer free or low cost spay and neuter programs, and encourage friends and family members to have their pets altered if possible.
• Support local programs and controlled hunts that target invasive species and help remove them from the regional ecosystem.
• Take steps to protect wild birds from known invasive predators, such as discouraging feral cats or protecting bird houses from snakes.
• Create safe, bird-friendly backyard habitats with native plants, supplemental feeders, fresh water and adequate shelter so birds have a reliable and predator-free zone to use.

Invasive predators take a heavy toll on local wildlife, including birds. By understanding what makes a predator invasive and how it can be a grave threat to birds, birders are better prepared to help restore their native ecosystems to a proper balance of predators and prey and take steps to protect birds from overwhelming predators.

Photo – Feral Pig © Duane Burdick