for National Geographic News
Invasive rats on ocean islands are threatening the survival of many of the world's seabirds, according to a new report.
The global analysis found that non-native rats have been observed preying on roughly a quarter of all seabird species, often with disastrous consequences. (See photos of rat-seabird conflict.)
The voracious rodents attack bird nesting colonies, eating eggs, chicks, and sometimes even adult birds.
Now 102 of 328 recognized seabird species are considered threatened or endangered by the World Conservation Union, with predation by invasive species ranking among the top dangers.
"Seabirds are important ecological actors in the oceans and on islands, but 30 percent of all seabirds are at risk of extinction," said study co-author Bernie Tershy of the University of California, Santa Cruz.
"Invasive rats are likely the single largest threat to seabirds," said Tershy, also a former grantee of the National Geographic Conservation Trust. (The National Geographic Society owns National Geographic News.)
Smaller seabird species and those that nest in burrows or rock crevices are particularly at risk, the study said.
That group includes storm-petrels, auklets, murrelets, and shearwaters, according to lead author Holly Jones of Yale University in New Haven, Connecticut.
"Rats can have a larger impact on entire seabird populations in species with adults that are small enough to prey on," Jones said.
"Burrow- and crevice-nesting seabirds share the same underground habitat [as rats], which makes a predation encounter more likely."
Traveling with humans as ship stowaways, three rats species native to Europe and Asia have become established on about 90 percent of the world's major islands and island chains, experts say. In many cases the original invasions occurred centuries ago.
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