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Sep
12
2009
Invasive species need to be removed in the right order
In the mid-1990s, conservationists were faced with a conundrum. Feral pigs had attracted golden eagles to the northern California Channel Islands, and the eagles were preying on island foxes. To keep the foxes from going extinct, managers had to remove both the pigs and the eagles. But in which order?
Trapping eagles wasn’t easy, and killing them outright was controversial. But removing the pigs first might encourage the eagles to eat more foxes. In the end, managers decided to start with the eagles. They captured 44 golden eagles from 1999 to 2006, only removing the pigs during the last two years.
The managers made the right decision, a team concludes in a new PLoS ONE study. The authors studied the prey remains of one golden eagle pair that had escaped capture and found that the birds did eat more foxes after the pigs were removed. Foxes rose from 17.5 to 51.5 percent of the eagles’ diet, they report, suggesting that the foxes might have gone extinct more easily on a pig-free island.
But conservationists can’t pat themselves on the back quite yet. Around the same time, 61 bald eagles also were introduced to one of the islands, with the thought that they might nudge out some golden eagles. Alas, the bald eagles now appear to be eating the foxes. Sometimes you just can’t win. – Roberta Kwok
Source: Collins, P., Latta, B., & Roemer, G. (2009). Does the Order of Invasive Species Removal Matter? The Case of the Eagle and the Pig PLoS ONE, 4 (9) DOI: 10.1371/journal.pone.0007005
Image © nickfree, iStockPhoto.com
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