Does the presence of burrowing seabirds increase local invertebrate abundance?

Abstract

International studies have shown that the marine nutrients introduced by seabirds can increase the abundance of terrestrial invertebrates, but to date there have been few studies on this aspect of invertebrate ecology in New Zealand. This paper reports on a study conducted on Motuora Island (Hauraki Gulf), a modifi ed island that retains a remnant breeding population of grey-faced petrels (Pterodroma macroptera gouldi). The aim of the study was to assess whether petrels have positive localised impacts on the abundance of ground invertebrates in general and on beetles in particular. Pitfall trapping was carried out at sites with seabird burrows and at sites without burrows. Invertebrates were sorted into broad taxonomic groups while beetles were sorted to species level. Beetle species were also extracted from burrow litter. The results indicate that petrels on Motuora do not have a large consistent effect on the overall abundance or biomass of ground invertebrates. However two beetle species were found to be more abundant in areas with burrows than in areas without burrows; Mesocolon sp. (Coleoptera: Leiodidae) and Eupines sp. (Coleoptera: Staphylinidae). Several other nidicolous beetle species were found in litter from grey-faced petrel burrows. Results suggest a number of beetle species utilize resources provided by seabirds, but further research is required to determine if seabirds have wider impacts on local invertebrate abundance.