Population estimatesPopulation estimates

Population estimates

There are no estimates before 1967, but it is known the global range had been severely reduced by the early 1900s. By 1967, the breeding population was limited to Christmas Island and estimated at 2300-3000 pairs (Nelson 1971). Mining in the northwest sector of the island commenced in 1970, consequently scores of chicks, adults and their nest trees were destroyed by clearing (Powell in Yorkston and Green 1997). In 1979/80 and 1982, Powell and Tranter (1981) resurveyed the population and, although they did not estimate total numbers, found that the distribution of nests had not changed significantly from 1967, despite large areas of further clearance. The total breeding population in 1983 was estimated at 1900 pairs (Reville et al. 1990a), after an estimated loss of 400 breeding pairs since mining commenced in 1970. Mining ceased in 1987. In 1991, the most recent survey, the population was estimated at 2500 pairs (Yorkston and Green 1997). The difference between the two most recent published estimates was due to discovery of further nesting areas on the northern side of the island, and also among the southern and southwestern areas of distribution, but was not thought to indicate an increase in population size (Yorkston and Green 1997). Preliminary results from a 2002 helicopter survey suggest that the population is not showing signs of change.