SummaryEstimates of the breeding status of the Wedge-tailed ShearwaterPuffinus pacificuson the Capricorn Group of islands in the southern Great Barrier Reef indicate that the size of the breeding population is much lower than previously thought (500 000 pairs). For the 1989–90 season 43% and 56% of burrows, on Heron and Erskine Islands respectively, supported breeding birds. Most occupied burrows featured lined nesting chambers. Burrow lengths ranged from 0.1 m to 2.35 m with a mean of 0.91 m. There was no relationship between burrow length and breeding activity.