A new method for calculating volume of excavated burrows: the geomorphic impact of Wedge-Tailed Shearwater burrows on Rottnest Island

1. Studies of ecosystem engineering may use burrow volume and soil displacement rate to quantify the impact of burrowing vertebrates. Calculations of burrow volume from morphometric measurements have previously treated burrows as rectangular or elliptical prisms. 2. Here we use burrows of the Wedge-Tailed Shearwater (Puffinus pacificus Gmelin, 1789) to demonstrate a new method for collecting morphometric data, and for mathematically modelling burrow shape used to calculate burrow volume. 3. Our method improves on previous estimates by better estimating the cross-sectional burrow shape, and by accounting for some of the variation in burrow width and height. 4. Wedge-Tailed Shearwater burrows were parabolic in cross-section, averaged 1.99 +/- 0.04SE m in length and had a mean volume of 0.06 +/- 0.00SE m(3). The shearwaters excavate at a rate of 7.75 m(3) ha(-1) year(-1) (10.51 t ha(-1) year(-1)) which ranks them above many geomorphic mammals. We suggest that this warrants further investigation into the role of burrowing seabirds as ecosystem engineers.