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Exotic Birds in Urban Environments: Part 3

November 27, 2007

Parts 1 and 2.

When we left off we had looked at an example of an attempt to control an invasive species and means in which such a species distributes. Can such experiences prepare us for future invasions?

Perhaps what we learn about distribution and expansion of invasive bird species can be put to the test in the case of a very recent arrival to North America, the Common Myna (Acridotheres tristis). The Common Myna or Indian Myna, native to southern Asia, is in the starling family and is similar in size and habits to the familiar European Starling. The bird has a long history of rapid expansion following introduction into exotic environments in Australia and several subtropical islands. They share several key properties with invasive birds in North America, namely their aggressive nature, high breeding success, and ability to nest near human settlements. Because of these characteristics, it was not long before they became a nuisance. In fact, native species in Australia and Hawaii, have had significantly lower breeding success since the introduction of the Common Myna in those places.

The Common Myna was first discovered in North America in 1983, when a population of six birds was found in the Miami area on a Christmas Bird Count. In the years since, the spread has been rapid, but not as rapid as originally suspected and remains small and widely scattered. While a thorough life history study of the species in North America has not yet been undertaken, it is suspected that the spread has been staunched somewhat by the establishment of the similar European Starling, with whom the Common Myna may compete directly for nesting sites and food. Like the European Starling, the Myna is a cavity nester and a generalist feeder able to adjust quickly to disturbed sites and appears to no disinclination to nest in close proximity to humans and other members of its own species.

Perhaps the best indication of what we may expect with these birds comes from Australia, where initiatives to control the population of Common Mynas have delivered mixed results. Because of concerns of the effects on native species, poison and destruction of roost site are not feasible. Traps have proven to be effective only on the short term. The birds are highly social and seem to be able to adjust to traps and danger areas, particularly if the trapped bird emits distress calls. Trials with Myna-specific traps that emphasize the comfort of the bird are inconclusive, as it is not known if these traps can be implemented on a large enough scale to affect the population of the Common Myna in any real way. Hopefully, the Common Myna’s impact on the avifauna in the United States will not be as severe as it appears to be in other areas. But without in-depth study on the Florida population, now becoming more self-sufficient by the year, the future of the bird in this country is unclear.

Upwards of 97 species of exotic birds can currently be found in North America, yet so far, only three, the European Starling, the House Sparrow, and the Rock Pigeon, and arguably a fourth in the House Finch, have population that can be considered to have affected native ecosystems on a continent wide scale. The common thread among the four species listed above seems to be an aggressive nature that allows these birds to survive in areas outside of the urban environment’s simplified ecosystem, as it seems that the majority of exotic species are unable to compete as well in rural areas. While exotics reach high levels of abundance and diversity in many cities across the continent, they have not yet expanded in the way starlings, sparrows and pigeons have. There could be a several reasons for this. First, the exotics are taking advantage of an ecosystem very different from those outside the urban/rural interface. Birds are certainly not alone in breaking into new territories. Exotic plants are an important food source for exotic birds. In fact, studies in Florida have shown that most non-native birds in the area feed primarily on non-native plants. Both exotic birds and plants may just be filling what niches are available and have been vacated by native species driven out by development. Such species seem to have difficulty expanding into ranges where native species have more than a foothold. This means that mitigating the effects of invasive bird species may be as simple as discouraging the use of invasive plant species.

A second reason for success of non-native species is elapsed time since introduction. This factor is critical for predicting success of exotic bird species. Those that have integrated themselves into our native avifauna are those that have simply had the most time to be here. This is a problem primarily because it may only be a matter of time before species such as the Monk Parakeet and Common Myna inevitably expand their current range in North America. This is especially concerning for species as historically destructive as Common Myna. Therefore, it is crucial for areas where exotic species are commonly found (e.g., southern Florida and California) to work with the United States Department of Agriculture to actively manage these species to prevent rapid range expansion.

There are many factors impacting populations of North America’s native bird species in a negative way. We certainly are not doing those species any favors by ignoring the effect of invasive birds from other continents. The avifauna of this country may never be free from European Starlings, House Sparrows, and Rock Pigeons. It is likely that we have to accept those species, but additional exotics should, and likely can be, prevented from getting out of hand.


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