Monday, July 20, 2015

When Killing Rats Is Essential for Wildlife

From Environment 360
comes this story about why aggressive rat eradication on islands is critical to protecting endangered wildlife, especially island endemic birds:

Despite the fact that islands comprise only three percent of the planet’s landmass, 95 percent of all known bird extinctions occur on them. According to The Nature Conservancy, a world leader in rodent eradication, rats alone have been responsible for an estimated 40 to 60 percent of recorded extinctions of island birds and reptiles.

This blog has gone over the rats-and extinctions numbers before, and reported too on what poisons work well and why even a single pregnant rat can provide enough genetic drift and mutation to overcome inbreeding depression.  We have even noted some success in such locations as Lord Howe Island and Rat Island in Alaska.

Now comes rumor of success on South Georgia Island in the middle of the Atlantic, just south and about 1,000 miles west of Tierra del Fuego, thanks to helicopters dropping tons of poison bait (see picture at top) in otherwise inaccessible locations.

Before rats arrived on ships of 18th-century seal hunters, South Georgia Island had sustained 27 species of seabirds in the world’s greatest concentration. But the invaders feasted on eggs and hatchlings, eliminating an estimated 90 percent of all birds on this sub-Antarctic island. By the 21st century, the South Georgia pipit, a terrestrial species found nowhere else on earth, was headed for almost-certain extinction.

The Team Rat project [recently completed] dwarfed all rodent eradications previously attempted. The island’s 1,450-square-mile surface is strewn with jagged, ice-bound peaks, 11 of them over 6,500 feet. What’s more, Team Rat — put together by the South Georgia Heritage Trust — was racing global warming. Glaciers kept rats out of large sections, but these barriers were melting rapidly. Two glaciers had already been lost, allowing the infestation to spread. Without the remaining glaciers, the northern and southern coasts would be united, and surviving birds would be history.

It will be another two years before Team Rat can positively declare the island rodent-free, but the prognosis couldn’t look better. Surviving glaciers sealed off three sections that could be treated independently. Birds are already recovering in sections completed in 2011 and 2013; and careful monitoring has revealed no sign of rats. In January 2015 the first successful nest of the South Georgia pipit was discovered in the 2013 section. 

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