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| Mute Swan (Cygnus olor), N. Pt. Marina, Lake Co, IL 1/14/2014 |
This pair of Mute Swans are part of an increasing population in the Great Lakes region, the result of earlier introductions of this Eurasian species. (This population increase is probably supplemented by the continuing use of this species in ornamental duck ponds.) Most of the increase in Illinois happened in the 1990s, although the first records appear to occur in the early 1960s. In contrast, our native Trumpeter Swans (Cygnus buccinator) were nearly wiped out by the 1900s, except for a few birds in Yellowstone National Park and an unsuspected Alaskan breeding population -- they were completely extirpated from the Great Lakes region. Reintroductions in Michigan and Minnesota, and later in Iowa and Wisconsin, have built up a fairly healthy population again, but the first Christmas Bird Count records in Illinois only occurred in the early 1990s, and they didn't approach Mute Swan numbers until 2010. (1)
One potential issue with the Trumpeter Swan recovery is that they can compete for habitat with Mute Swans; indeed, the USFWS and several state agencies have called for measures to control Mute Swan populations to avoid this problem. Needless to say, the idea of killing big, pretty white birds is not viewed favorably in some quarters. Those opposed to the idea have argued that ecologically there isn't much difference between the species. This may well be true, although it seems to me that every time we learn something new about ecology, it drives home how much more there is for us to learn. But either way, it ignores an important point: if Mute Swans are extirpated in North America, the species as a whole is still in good shape; they're still quite common in much of their native Eurasian range. (Although there were serious declines in the 1980's, believed to be caused by extensive use of lead shot by waterfowl hunters, causing lead poisoning in birds that swallowed spent pellets for gizzard stones. This has been a common problem in the US as well, leading to a ban on lead shot for waterfowl hunting in both Europe and the US.)
But what if an exotic species, one that conservationists would normally dislike because of the potential effects on native critters, were no longer found in their native range? Then what is the appropriate response? Should we intentionally cause the extinction of one species to avoid potential problems with other, more preferred species?
I don't have an answer for these questions, but the idea isn't as far-fetched as it seems. I don't know of any common exotic species that is endangered in it's native home, but there are some that appear to be headed that way. Brush-tailed Rock Wallabies (Petrogale penicillata) are listed as Near-threatened by the IUCN, for example, and have experienced declines over much of their Australian range. Which makes the populations on several of New Zealand's offshore islands, where they're now seen as pests, potentially important for conservation. (2) Likewise, the small population in the mountains above Waikiki, Hawaii may prove to be important. (Those animals are few and secretive enough that we don't know what impacts they've had, and the Islands have enough other situations for wildlife managers to deal with.)
Here's another example:
Mandarin Duck (Aix galericulata), Omaha Zoo, 12/30/11
These guys are native to eastern Asia, and while they're still doing well in Japan, they're listed as endangered in China. The world's second largest population is in Great Britain. How should we view them, as potential ecological threats or as a valuable reserve in what could become a fight to preserve the species as a whole?
I'll repeat that I don't have an answer -- but I'll also point out that whether we come up with an answer or not, time doesn't give the luxury of remaining undecided. Sooner or later we will answer the question with our actions, even if we do so without realizing that there was even a question to be asked.
(1) National Audubon Society (2010). The Christmas Bird Count Historical Results [Online]. Available http://www.christmasbirdcount.org [2014]
(2) Shaw, W.B.; Pierce, R.J. 2002: Management of North Island weka and wallabies on Kawau Island. Department of Conservation Science Internal Series 54. Department of Conservation, Wellington. ISBN 0-478-22272-6.
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