Abstract for presentation at Biodiversity Extinction Crisis Conference - A Pacific Response

Nutrient inputs from seabirds affect the population dynamics of mammals on islands in Western Australia

  • Annabelle Stewart, School of Animal Biology, The University of Western Australia, Australia
  • Dr Roberta Bencini, School of Animal Biology, The University of Western Australia, Australia
  • Dr Tony Friend, Department of Environment and Conservation, Western Australia, Australia

    • By increasing concentrations of soil nutrients, burrowing seabirds can increase the primary productivity of islands, which can have flow on effects to other levels in the trophic system. Colonisation by wedge-tailed shearwaters (Puffinus pacificus) was found to affect the population dynamics of an endangered marsupial, the dibbler (Parantechinus apicalis), and house mice (Mus domesticus) on the Jurien islands. Animals were trapped for a period of 30 months, and their population structure, body condition, longevity and diet were examined.

    Densities of seabirds and soil nutrient concentrations were highest on Whitlock Island, intermediate on Escape Island, and lowest on Boullanger Island. Peak densities of dibblers were highest on Whitlock Island (36.2ha-1), intermediate on Escape Island (18.6-1), and lowest on Boullanger Island (8.2ha-1). Peak densities of mice were higher on Whitlock Island (582.0ha-1) than on Boullanger Island (180.8ha-1), and the mice on Whitlock Island had better body condition and longer life spans than those on Boullanger Island.

    For dibblers, body condition was best and life spans were longest on Whitlock Island, intermediate on Escape Island, and lowest on Boullanger Island. Dibblers exhibit facultative die-off, where males die after an intense breeding season. Whitlock Island supported greater numbers of male dibblers that survived to an older age compared to those on Boullanger or Escape islands, suggesting a link between resource availability and male die-off in dibblers.

    The densities, body condition and life span of mammals on the islands may be attributed to the densities of seabirds and their influence on productivity, including food availability. Pitfall trapping studies showed that there were greater numbers of invertebrates on Whitlock Island (26 invertebrates/pitfall), followed by Escape Island (23 invertebrates/pitfall), then Boullanger Island (20 invertebrates/pitfall).

    This study highlights the positive impact that burrowing seabirds can have on their nesting environments.

    Conference Organiser - ICMS Pty Ltd