Currently 102 of 328 recognized seabird species are considered threatened or endangered, with predation by invasive species ranking among the top reasons. A new study published in February's edition of the journal Conservation Biology suggest that rat invasions likely pose the single largest threat to this population of unassuming birds.
Since most seabirds breed on islands, many have evolved in the absence of any land-based predators, and have no adaptation to avoid predation by rats. The birds have a hard time switching their breeding locations to different islands to escape danger, since many are genetically programmed to return to their birthplace for breeding.
The global analysis indicates that non-native rats have been observed preying on ~25% of all seabird species. Smaller species and those that nest in rock crevices or burrows, such as storm-petrels, auklets, murrelets, and shearwaters, are especially at risk. The hungry rats attack bird nesting colonies, eating eggs, chicks, and sometimes even adult birds.
Experts say that 3 rat species native to Asia and Europe are now established on about 90% of the world's major islands and island chains. This has been achieved by traveling with humans as ship stowaways, and in many cases the original invasions occurred hundreds of years ago.