Burrowing seabirds are returning to Macquarie Island following the eradication of cats and a blitz on mice, rats and rabbits.

Wildlife ranger Bree Hunter of the Tasmanian Parks and Wildlife Service says the island’s burrowing petrels appear to be making a comeback, although the numbers and breeding success of all species returning to their sub-Antarctic nesting ground have yet to be quantified. An annual, island-wide census of northern and southern giant petrels began in 2011.

The Australian and Tasmanian governments have provided almost $25 million to eradicate rabbits, rats and mice from Macquarie Island. Are the benefits of such programs possible to predict?

According to Chris Wilcox of CSIRO and Leader of the CERF Marine Biodiversity Hub Management Options theme, studies of how birds respond to predator control programs are essential to guide and prioritise conservation efforts, and to predict the costs and benefits.

Dr Wilcox worked with Jennifer Lavers of the Tasmanian Museum and Art Gallery (formerly a CERF postdoctoral student at the University of Tasmania), and Josh Donlan of Advanced Conservation Strategies and Cornell University, to review studies of predator control programs, and efforts to predict their success. This research found that the direct benefit to birds was quantified in only 20 per cent of more than 800 successful invasive mammal eradications worldwide.

For the majority of bird species studied, predator removal resulted in increased productivity and survival. The productivity increase was 25 per cent on average. Overall, both the characteristics of the predator and the characteristics of the bird influenced the benefit from eradication.

Eradications of mammal predators, such as rats and stoats, had the best results, and birds nesting on or near the ground or in burrows were especially vulnerable to predation. Seabirds and other surface nesting birds would therefore benefit more from predator removal than tree-dwelling species. Smaller birds and birds with larger eggs also benefited more from eradications.

The best model for predicting the change in productivity from predator removal incorporated bird body mass, egg mass, predator type, nest type (and an interaction between body mass and nest type).

Obstacles to predictive ability included availability, quality and bias in reporting (null effect can be difficult to publish), and idiosyncratic circumstances (such as co-existence of the tiny Thin-billed Prion, Pachyptila belcheri, with mice, cats, and black rats on the Falkland Islands).

The predicted increase in productivity resulting from predator removal alone was adequate to reverse population decline for between a third and two thirds of the bird species considered. This indicates that while eradications have substantial benefits for biodiversity conservation, in some cases additional actions are needed.
 

Photo:  Heading out to hunt, Macquarie Island.  Copyright:  Chris Crerar, http://chriscrerar.com.au/

Related information:

CERF Marine Biodiversity Hub

Jennifer L Lavers, Chris Wilcox and C Josh Donlan (2010). Bird demographic responses to predator removal programs, Biological Invasions Vol 12, No 11, 3839–3859.

Macquarie Island Pest Eradication Project http://www.parks.tas.gov.au/?base=13166
Project manager, Keith Springer