Honolulu Star-Advertiser © Susan Scott
July 28, 2018
When in 2004 I worked at Palmyra Atoll, about 1,000 miles south of Hawaii, rats were crawling out of the woodwork. Really. Gray whiskered faces peeked from wall cracks, waiting for us to leave so they could get to destroying peanut butter jar lids, backpacks bearing granola bar scents and my sweat-soaked sandals.
Once, as I squatted down to put out ant bait, a rat beneath a nearby bush locked eyes with me. This midday stare was unusual for the nocturnal rodent, but in the absence of predators or poison, the creatures had grown bold. And multiplied. At the time, it was estimated that 30,000 rats inhabited the 25 islands of Palmyra Atoll, a land mass totaling barely 2 square miles.
Atoll biologists Coral Wolf and Alex Wegmann
in emerging Pisonia trees at Palmyra Atoll.
Photo courtesy Island Conservation.
Scientists from the U.S. Fish and Wildlife Service, The Nature Conservancy and Island Conservation studied the rat problem at Palmyra for the next seven years, and in 2011 the group was ready to rid this biologically unique atoll of all rodents. A team of 41 people from five countries worked for 28 days spreading an anticoagulant bait throughout the atoll’s islands, including using slingshots to get to the tops of coconut trees, where rats hung out.
And then there were none. The eradication of the non-native rats succeeded, and now, seven years later, researchers are seeing the shoots of their labor.
Real shoots. In the past, as soon as mature Pisonia trees, a species unique to Pacific atolls, dropped their seeds, the rats ate them. No more. Today, Pisonia saplings thrive in Palmyra as they did years before human introductions upset the system.
You might not think restoring native tree growth would help the coral reefs that surround the atoll, but the systems are linked. As Pisonia once again grow throughout the islands, their branches offer places for tree-nesting seabirds such as white terns, red-footed boobies, noddies and frigate birds to raise their chicks. The birds’ droppings fertilize the ground below. But during the frequent bursts of rain there, guano washes into the ocean, providing the surrounding coral reefs with the nutrients they need to stay healthy.
Ground-nesting birds are also returning to the atoll, contributing even more fertilizer to the trees and reefs. In addition, biologists discovered two species of land crabs previously unknown in the atoll, making a total of nine land crabs native to Palmyra.
And another bonus: Without rats for blood meals, the mosquitoes that plagued human workers have died out.
Even with all this good news, island rat eradication has its critics. Some people protest the killing of mammals, and others argue against the anticoagulant used to poison them.
This wildlife management strategy, however, should not be controversial. The science behind it is sound (the poison doesn’t harm invertebrates or fish), and the remarkable results speak for themselves.
Palmyra’s crabs, by the way, were all for the eradication, viewing 30,000 rat carcasses as a free-for-all feast. In 48 hours the dead bodies were gone, fur and all — except for the teeth. No one likes rat teeth, even crabs.