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Invasive birds — some welcome, others not

Some species had been deliberately introduced to the country, while others came on their own

Alien invaders in your backyard? I recently saw three from my kitchen window, and I was pleased to see them, as they weren’t from outer space. These invaders were Eurasian collared-doves, which are spreading across the southern part of Manitoba.

The Eurasian collared-dove first arrived in the New World in the 1970s. Some were brought as pets to the Bahamas and escaped from a pet store, while others were deliberately set free. By the 1980s they had reached south Florida, and from there began their spread in a northwesterly direction across the U.S. They became the fastest-spreading invasive avian species known so far, and have now been sighted all the way to Alaska, although they are still relatively rare in Manitoba.

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The collared-dove is larger than our native mourning dove, greyish beige in colour, with a narrow, black half-collar edged with white around the back of the neck, but lacking the black spots common on the wings and sides of the mourning dove. Their call is a three-syllable “coo-COO-coo.” They are ground feeders and, unlike our native doves, do not migrate seasonally, so in winter they frequent yards with bird feeders or farmyards.

Bird-lovers fear this species might have a negative impact on mourning doves, but so far research indicates that the native population actually seems to be greater when they coexist with collared-doves. For more information and pictures go the The Cornell Lab of Ornithology website.

Although the collared-dove has been welcomed by most, other invading species have had negative impacts, such as the house sparrow (a.k.a. English sparrow). A few of these, probably less than 50, were introduced in Brooklyn, N.Y. in the early 1850s, because they were considered attractive and might help to control insect pests. They spread rapidly across the U.S. and into Canada in only 50 years — some considering them pests, others admiring them for being able to withstand our winters. By 1917, the house sparrow was already being blamed for the decline of songbirds, as it competes for food and nesting sites. Local birders with lines of bluebird nest boxes often discover them taken over by sparrows.

A third common invading species, which was also deliberately introduced, is the European starling. A group called “The American Acclimatization Society,” decided to bring to the U.S. every bird species mentioned in the plays of William Shakespeare. Many species failed, but the starling took hold. Over two years (1890-91) about 100 of them were released in New York City. These quickly spread across the continent except the Far North, negatively affecting many native birds, as well as damaging crops and eating grain set out for cattle. Estimates today put their number at 200 million, despite efforts to control them. One program in California in the 1960s resulted in nine million slaughtered, but enough remained to continue reproducing. Damage caused by starlings can be particularly bad because they often congregate in enormous flocks, which have occasionally caused airplane crashes. They are also carriers of both human and livestock diseases, and impact many songbirds by bullying them from their nests and food.

Another of our birds (introduced in the 1600s) is the rock pigeon, said to have been brought by settlers to Nova Scotia in1606, and later to Virginia and Massachusetts, and now common in cities and towns across the world.

A non-native bird that rural residents might recognize is the grey partridge, introduced as a game bird in the early 1900s. It has spread across prairie areas of southern Canada/northern U.S., and is most often seen in small flocks.

Some birds have invaded the Americas on their own, such as the Old World cattle egret. Around 1880 it reached the northern coast of South America, and by 1940 spread to Florida and across the U.S. In southern Manitoba this egret is now found near wetland areas such as Whitewater Lake, near Boissevain, frequently around cattle herds.

How introduced species affect the ecosystem varies from species to species. Often, the negatives — competition for nesting sites and food, consumption of crops, transmission of diseases, and disruption of the predator/prey balance — outweigh the positives. This has led the World Conservation Union to label invasive species as “the second most significant threat to biodiversity, after habitat loss.”

Even so, I’ll still gladly welcome the Eurasian collared-doves at my feeders.

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