Biopedturbation by an island ecosystem engineer:: burrowing volumes and litter deposition by sooty shearwaters (Puffinus griseus)

Seabirds can influence entire island ecosystems through the effects of their burrowing and of their underground deposition of vegetation on biotic and abiotic island processes. This study quantifies the extent of these effects at three sooty shearwater breeding islands in southern New Zealand, with the aim of assessing the importance of this species as an ecosystem engineer. Mean burrow volumes ranged between 158.2 and 528.1 m(3) ha(-1). Between 18 and 34% of the ground surface was undermined by burrow space on the three islands. This extent of burrowing is comparable to that of fossorial mammals, widely recognised as ecosystem engineers. Mean vegetation inputs (dry weight), transported underground by birds and incorporated into nests, varied between 33 and 96 g m(-2). The implications of the biopedturbation caused by sooty shearwater burrowing to the extent measured in this study may be profound for some ecosystem processes, and certainly warrants further research.