Predation by rats are a particular problem, on Pitcairn and Henderson. Modelling indicates that petrel numbers have dropped from a possible 5 million pairs before rats were introduced to just 40,000 pairs today, and the Henderson petrel is threatened with global extinction. Other species are also being affected seriously, with rats predating on - and competing with - Henderson's endemic land-bird species, snails, insects and flora, as well as on the hatchlings of the nesting green turtle population. A successful rat eradication programme exterminated rats on Oeno and Ducie, resulting in healthy breeding bird populations on these atolls.