Invasive birds can be problematic for wildlife, agriculture and even human health, but many birders don’t understand exactly what an invasive bird species is. By knowing how a species can be classified as invasive, better wildlife control measures can be taken to protect native birds.
While the exact classification of a species as invasive or non-native can be delicate, an invasive species is typically defined as one that is not native to the area and is threatening to the local ecosystem, local economy or human health. Not all non-native birds are therefore naturally invasive: many of them can adapt to new niches in different ecosystems without harmful effects. When a species has a drastic impact in a new area, however, it is considered invasive. Furthermore, the same species that may be considered invasive in one region may not be harmful in a different region, and would thus simply be considered non-native.
Some of the most familiar bird species widely (though not universally) considered invasive include:
Each of these birds is regularly considered invasive in North America, and many of them are also invasive in other parts of the world.
How Introduction Happens
There are several ways that a non-native bird species can “invade” different regions, both naturally and with human assistance.
- Geographic Expansion: Birds that rapidly expand their ranges and crowd out resident species may be considered invasive, particularly if the expansion is damaging to other species or ecosystems or if there is an artificial reason behind the range shift, such as habitat loss.
- Deliberate Import: Some bird species have been deliberately imported to new areas for various reasons. This happened in North America with the house sparrow when European settlers wished to introduce familiar birds from their homelands to their new country, without regard for the long-term consequences. Other bird species may be deliberately imported in attempts to control insect populations or for other well-meaning purposes with disastrous consequences.
- Escape: Species popular as pets may regularly escape confinement or be released from unscrupulous retailers and subsequently establish wild populations. Other bird species may escape from farms or contained breeding grounds and grow populations in the wild that can impact resident birds.
- Accidental Import: Some bird species may be inadvertently introduced to new areas through accidental imports. This can happen when a bird stows away on a plane or ship and escapes in a distant region, though many times the birds are not able to establish a wild population because of a lack of breeding partners.
Invasive birds can cause a wide range of problems, not only for native species but also for the ecosystem altogether. Common problems with invasive birds include:
- Competition for nesting sites
- Competition for food sources
- Consumption of agricultural crops
- Transmission of diseases
- Disruption of ecological predator/prey balance
In the case of invasive birds, these negative effects outweigh the potentially positive gains from new species, such as biological diversity and the aesthetics of enjoying new birds.
Many government agencies and wildlife conservation groups seek to manage non-native bird species as appropriately and humanely as possible. Tactics may include disrupting or destroying nests, targeted poisoning, trapping, hunting and other ways to reduce invasive populations. In many areas, species classified as invasive are not protected under wildlife conservation measures or migratory bird treaties, but individual birders and homeowners should contact their local wildlife management office for details before attempting any control techniques on their own.
Invasive birds can be controversial among birders for several reasons. Birders who relish the plaintive chirps of bluebird nestlings, for example, may feel very negatively about invasive house sparrows after watching a house sparrow viciously attack and kill young birds and adult bluebirds. Birders who also enjoy hunting, however, may approve of carefully cultivated invasive species that allow waterfowl hunting to continue. Some birders simply enjoy all birds, native or not, and are dismayed when aggressive tactics are taken to control any species.
Whatever your personal opinion on invasive birds, understanding what “invasive” means and how an invasive species can harm local ecosystems can help you appreciate the diversity of birds in your region. For good or bad, many invasive species are here to stay.