Register      Login
Wildlife Research Wildlife Research Society
Ecology, management and conservation in natural and modified habitats
Shopping Cart: ( empty )
You are here: Home > Journals > WR > WR07037
RESEARCH ARTICLE
Contents Vol 34(6)

Detecting predation of a burrow-nesting seabird by two introduced predators, using stable isotopes, dietary analysis and experimental removals

Grant A. Harper
+ Author Affiliations
- Author Affiliations

University of Otago, PO Box 56, Dunedin, New Zealand. Present address: Department of Conservation, PO Box 743, Invercargill, New Zealand. Email: gharper@doc.govt.nz

Wildlife Research 34(6) 443-453 https://doi.org/10.1071/WR07037
Submitted: 23 March 2007  Accepted: 20 September 2007   Published: 2 November 2007

Abstract

Burrowing seabirds are vulnerable to extirpation by introduced predators such as rats, but much evidence of predation is circumstantial. On Taukihepa, an island off southern New Zealand, two possible predators exist with sooty shearwaters (Puffinus griseus): the weka (Gallirallus australis), a large rail, and the ship rat (Rattus rattus), both introduced to the island. It was expected that chick predation would be principally by weka, the much larger of the two predators. To measure losses of sooty shearwater chicks to weka or rats, nests were monitored with burrow-scopes at six sites in the summers of 2003–04 and 2004–05. In three of the sites rats were removed on 4-ha grids by trapping. In the other three sites rats were not trapped. In addition, weka were removed from all six sites in 2005. Concurrent diet analysis of weka and rat stomachs was undertaken as well as stable isotopic analysis (δ13C, δ15N) of samples from rats and weka. These were compared with possible prey items including sooty shearwaters. Additional stable isotope samples were taken from Pacific rats (Rattus exulans), a small rat species present with weka and sooty shearwaters on nearby Moginui Island. Weka diet comprised ~40% of bird remains by volume and calculations using Isosource, an isotopic source portioning model, estimated sooty shearwaters contributed 59% (range: 15–71%) of weka diet during the sooty shearwater chick-raising period. Ship rats, in contrast, had very depleted δ13C isotope signatures compared with sooty shearwaters and bird remains contributed <9% of diet by volume, with Isosource calculations suggesting that ship rats consumed more passerine birds (mean: 30%; range 5–51%) than sooty shearwaters (mean 24%; range: 0–44%). In both summers, more chicks were lost on sites from which rats had been removed than on control sites. When weka were removed in 2005, fewer chicks were lost than in 2004 and significantly fewer weka-killed chicks were found on weka-removal sites than on non-removal sites. Weka were the principal predator of sooty shearwater chicks, depredating an estimated 9.9% of nests. Combining several techniques quantified the loss and identified the principal predator of a seabird in decline.


Acknowledgements

This work is a contribution from the Kia Mau Te Titi Mo Ake Tonu (Keep the Titi Forever) Research Project, funded by a Foundation of Research Science and Technology Post-Doctoral Fellowship (UOOX0232), the Command Oil Damage Restoration Fund, through Oikonos (USA) and Ka Mate Nga Kiore Committee. The Rakiura Titi Island Committee and Rakiura Titi Island Administering Body provided permission and guidance during the research. Many thanks to the volunteers from the Rakiura mutton-birding community and elsewhere who assisted and to the many island manu owners who permitted access and often assistance. Ron Bull deserves special thanks for allowing us to use his whare. South West Helicopters assisted with transport. The staff of the Kia Mau Te Titi Mo Ake Tonu (Keep the Titi Forever) Research Project were particularly helpful and great company. Many staff of the Zoology Department, University of Otago, also assisted. This research was carried out under the University of Otago Ethics approvals 102/02 and 85/04. Keith Hobson, Richard Holdaway and Mark Drever made useful comments on the manuscript.


References

Anonymous  (1934). Few muttonbirds. In ‘Western Star’, 13 April. Riverton, N.Z.

Atkinson I. A. E. (1985). The spread of commensal species of Rattus to oceanic islands and their effects on island avifaunas. In ‘Conservation of Island Birds’. (Ed. P. J. Moors.) pp. 35–38. ICBP Technical Publication No. 3. (ICBP: Cambridge, UK.)

Bell B. D. (1978). The Big South Cape Islands rat irruption. In ‘The Ecology and Control of Rodents on New Zealand Nature Reserves’. (Eds P. R Dingwall, I. A. E. Atkinson, and C. Hay.) pp. 33–45. (Department of Lands and Survey, Wellington, NZ.)

Bried, J. , and Jouventin, P. (1999). Influence of breeding success on fidelity in long-lived birds: an experimental study. Journal of Avian Biology 30, 392–398.
| Crossref | GoogleScholarGoogle Scholar | Burger J., and Gochfeld M. (1994). Predation and effects of humans on island-nesting seabirds. In ‘Seabirds on Islands: Threats, Case Studies and Action Plans’. BirdLife Conservation Series No. 1 (Eds D. N. Nettleship, J. Burger, and M. Gochfeld.) pp. 39–67. (BirdLife International: Cambridge, UK.)

Carroll, A. L. K. (1963). Food habits of the North Island weka. Notornis 10, 289–302.
Cunningham D. M., and Moors P. J. (1996). ‘Guide to the Identification and Collection of New Zealand Rodents’. 3rd edn. (Department of Conservation: Wellington.)

Cunninghame H. F. (2006). The comparative ecology of Stewart Island weka (Gallirallus australis scotti) on islands with and without seabirds. M.Sc. Thesis, University of Otago, Dunedin.

Dalerum, F. , and Angerbjörn, A. (2005). Resolving temporal variation in vertebrate diets using naturally occurring stable isotopes. Oecologia 144, 647–658.
| Crossref | GoogleScholarGoogle Scholar | Drummond J. (1910). The Mutton-birders. ‘Otago Witness’, 10 May. Dunedin, NZ.

Gales, R. P. (1982). Age- and sex-related differences in diet selection by Rattus rattus on Stewart Island, New Zealand. New Zealand Journal of Zoology 9, 463–466.
Heather B. D., and Robertson H. A. (1996). ‘The Field Guide to the Birds of New Zealand’. (Viking: Auckland, NZ).

Hobson, K. A. , Drever, M. C. , and Kaiser, G. W. (1999). Norway rats as predators of burrow-nesting seabirds: insights from stable isotope analyses. Journal of Wildlife Management 63, 14–25.
| Crossref | GoogleScholarGoogle Scholar | Innes J. G. (2005). Ship rat. In ‘The Handbook of New Zealand Mammals’ 2nd edn. (Ed. C. M. King.) (Oxford University Press: Melbourne.)

Johnston, P. N. (1982). Botanical notes on some southern New Zealand islands. New Zealand Journal of Botany 20, 121–130.
Lyver P. O., Hamilton S., McKenzie M., Dickson I., Dooher T., Broad T., and Moller H. (1998). burrowscope for examining petrel nests in burrows. Conservation Advisory Science Notes 209. Department of Conservation, Wellington.

Lyver, P. , Moller, H. , and Thompson, C. (1999). Changes in sooty shearwater (Puffinus griseus) chick production and harvest precede ENSO events. Marine Ecology Progress Series 188, 237–248.
| Crossref | GoogleScholarGoogle Scholar | Moors P. J., and Atkinson I. A. E. (1984). Predation on seabirds by introduced animals, and factors affecting its severity. In ‘Status and Conservation of the World’s Seabirds’. (Eds J. P. Croxall, P. G. H. Evans, and R. W. Schrieber.) pp. 667–690. ICBP Technical Publication No. 2. (ICBP: Cambridge.)

Newman, J. (2006). Peter and Joyce Topi. Titi Times 17, 12–13.
Norman F. I. (1985). Localised declines in colonies of the short-tailed shearwater: an explanation. Papers and Proceedings of the Royal Society of Tasmania 119, 103–107.

Ogden, L. J. E. , Hobson, K. A. , and Lank, D. B. (2004). Blood isotopic (δ13C and δ15N) turnover and diet-tissue fractionation values in captive dunlin (Calidris alpine pacifica). Auk 121, 170–177.
| Crossref | GoogleScholarGoogle Scholar | Sansom J. (1984). The climate and weather of Southland. New Zealand Meteorological Service Miscellaneous Publication No. 115. New Zealand Meteorological Service, Wellington.

Scofield, R. P. , and Christie, D. (2002). Beach patrol records indicate a substantial decline in sooty shearwater (Puffinus griseus) numbers. Notornis 49, 158–165.
Warham J. (1996). ‘The Behaviour, Population Biology and Physiology of the Petrels.’ (Academic Press: London.)

Warham, R. D. , Wilson, G. J. , and Keeley, B. R. (1982). The annual cycle of the sooty shearwater Puffinus griseus at the Snares Islands, New Zealand. Notornis 29, 269–292.


Ylönen, H. , Jacob, J. , Davies, M. J. , and Singleton, G. R. (2002). Predation risk and habitat selection of Australian house mice Mus domesticus during an incipient plague: desperate behaviour due to food depletion. Oikos 99, 284–289.
| Crossref | GoogleScholarGoogle Scholar |