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Exotic Birds in Urban Environments: Part 2

November 20, 2007
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Part 1 is here.

When we left off I was discussing the respective fortunes of the “classic” exotic species in North America. While starlings, House Sparrows, and pigeons have achieved nationwide dispersal, are there any others out there with the potential for the same?One such exotic species is the Monk Parakeet (Myiopsitta monachus), now widely established in several urban centers across the country. The Monk Parakeet is native to the pampas of South America, where its giant communal stick nests adorn what few trees stand on the plains of Argentina and Brazil. These nests are unique to the species, as all other parrots nest in cavities. Additionally, they serve as a limiting factor for the colony, with birds rarely ranging too far from them. There is evidence from studies in the bird’s native range, that the parakeets are cooperative nesters as well as colonial, with fledglings from previous broods helping raise the current group of young birds. 

The Monk Parakeet’s introduction to North America is an interesting story. With the development of a vaccine for psittacosis in the late 1960’s, the market for imported parrots as pets in the United States boomed. According to records from the US Fish and Wildlife Service, in 1971, over a million birds were imported, of which only around 27,000 were Monk Parakeets. It was not long , though, before fears of Newcastle disease prompted the shutdown of the industry. Soon after, parrots were seen regularly outdoors, released by uninterested owners or having escaped from faulty cages. Monk Parakeets, native to the temperate zone, fared better than their tropical cousins. They seemed to take to their new environs, establishing colonies in not only warm weather locales like Los Angeles and Miami, but also Chicago and New York City. The birds did so well that the Fish and Wildlife Service, wary of repeating the same attitude that lead to nationwide invasions of Starlings and House Sparrows, initiated a “retrieval” plan. The massive nests were easy targets, and hunters either knocked the nest down or shot the birds on their nightly return. Despite these measures, or perhaps because they failed to finish the job sufficiently, the Monk Parakeets survived and still can be found in colonies larger than those that were considered to be potential vectors for disease.

Research on the Monk Parakeets impact on native species is inconclusive. Anecdotal evidence suggests that the birds have little effect. The main problem with the birds appears to be their affinity for nesting atop power structures, presumably for the warmth. The nests eventually reach a size that causes damage to the facility and subsequent power outages. In Florida, it has been estimated that the birds cause nearly three power outages per day throughout the state, causing upwards of half a million dollars per year in maintenance. Attempts to disrupt the colony using owl decoys and traps were ineffective. The only successful way to stop the birds was to completely remove them along with the nest. Otherwise, what birds were left would immediately attempt to rebuild. Extermination of the parakeets is made even more difficult by citizens who see such exotics as desirable, and efforts to remove them often become so contentious that they are simply abandoned.

Although it has been nearly 40 years since the parakeets first arrived in North America, the populations have yet to expand in any real way beyond the cities in which they were originally established. This is interesting since North America was once home to a native psittacid, the Carolina Parakeet (Conuropsis carolinensis), which was found across the southeast and as far north as where the Monk Parakeets are established today. The Carolina Parakeet was seen as an agricultural nuisance as it destroyed seed crops across its range, eventually leading to the widespread hunting that caused its extermination in 1918. Worries that the Monk Parakeet might fill this niche and become a nuisance itself have proven somewhat unfounded. The Monk is much more of a generalist feeder than the Carolina was and therefore finds all it needs in the urban environment it has made its own. While the Monk Parakeet does appear to have established self-sufficient populations in many US states, their slow dispersal does not seem to place them as a threat in the manner of the three classic exotics mentioned earlier. However, if the bird’s populations grow to exceed carrying capacity in urban environments, we may begin to see Monk Parakeets in the urban-rural interface, where such fears of agricultural impact may well be realized.
Introduced species are often easy to distinguish from native species and while we are familiar with starlings, sparrows, and pigeons, invasive species can also be more subtle. Such is the case with the expansion of the House Finch (Carpodacus mexicanus) in eastern North America. The House Finch presents an interesting case in that the bird is native to North America. Prior to 1940, it was exclusively a bird of the western United States. Following the release of several individuals illegally destined for the pet trade in New York, the bird became established in the area and was seen regularly thereafter. Christmas Bird Count records from subsequent years chronicle the birds rapid expansion until the eastern population met the western population as recently as 1990 and the bird had true continent-wide distribution. This is probably due to the fact that its nesting and foraging requirements complement human-altered habitat conditions remarkably well. The spread of the House Finch was remarkably similar in scope to that achieved by the European Starling and House Sparrow a generation before.
At the time, the House Finch was seen as a native species and seemed to have little interspecific impact. As the population expanded however, evidence mounted that the House Finch, itself an aggressive feeder and disperser had negatively affected populations of Purple Finches (Carpodacus purpureus) on their winter grounds in the eastern United States. It even seemed to have a negative effect on populations of another introduced species, the House Sparrow. As it turns out, House Finches share many of the characteristics that made the classic exotics such efficient invaders, despite the fact that they were not, and still are not, considered to be exotics in the same sense. House Finch fledglings in eastern North America have a extremely high survival rate, upwards of 75%. The birds disperse widely using the “jump” method, in which populations of widely dispersing individuals become established ahead of the regular diffusion dispersal of the general population. It is suspected that this type of dispersal is common to invasive species in general, and because the rapid distribution of the House Finch occurred in recent time, we are able to observe the means of dispersal in a way we were unable to do with previous invasions.
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8 Comments
  1. John permalink
    November 20, 2007 11:26 am

    If power companies buried their cables instead of making them look like trees with central heating, power outages would not be a problem.

  2. slybird permalink
    November 20, 2007 11:32 am

    Excellent work! You write really well.

    I knew there was an impact between House Finches and Sparrows, but not between HOFIs and PUFIs. Do you elaborate later on in the essay?

    Regarding Monk Parakeets… do you know references to research on the limits to dispersal or carrying capacity?

    Cheers,
    Nick

  3. slybird permalink
    November 20, 2007 11:32 am

    Oh and you misspelled the name of Purple Finch

  4. November 20, 2007 5:30 pm

    Oops, thanks Nick.

    The correlation between House Finch increase and Purple Finch decline admittedly may not be completely proven. There’s a paper on the subject from 1991 by Beltoff called Aggression and Dominance in House Finches published in The Condor that suggests that House Finches played some role but decline of Purple Finches may be better attributed to habitat disturbance (which tends to favor House Finch) and seasonal ebbs in population which seem to be characteristic of all the boreal finches.

    For Monk Parakeets, Eberhard’s Breding Biology of the Monk Parakeet from 1998 in the Wilson Bulletin looks to be the bible on the bird, though it focuses mostly on the wild population. I think the jury’s still out on the feral pops in the US.

  5. November 20, 2007 5:35 pm

    My mistake, the Beltoff paper is more about intraspecific competition. The Purple Finch this is more alluded too than actually addressed.

  6. Greg permalink
    November 20, 2007 6:03 pm

    Really interesting read….

  7. Larry permalink
    November 20, 2007 7:27 pm

    Very informative article, and well written. I’ve seen Monk Parakeets in Connnecticut.Funny how people dislike certain birds but when they’re gone people want them back.

  8. Harrison J. Vega Silva permalink
    May 1, 2008 11:22 pm

    nice blogs, you like soo much the birds, that nice I has soo much birds in Puerto Rico. check my blogs vegatones.blogspot.com

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