A model for the management of the invasive ruddy duck to reduce interbreeding pressure on the white-headed duck

Abstract

Non-native species are considered the second most important threat to global biodiversity after habitat loss and are a leading cause of animal extinctions. The North American ruddy duck Oxyura jamaicensis established a feral population in the UK over 40 years ago, and is now endangering the globally threatened white-headed duck Oxyura leucocephala through hybridisation. We utilised a simple Monte Carlo spreadsheet model, which includes uncertainty and can be used for any invasive species, to assess the time-frame for successful control. Data on changes in numbers of ruddy duck at the main UK wintering sites were collected during a regional control trial. A single model, which included density-dependent and density-independent population growth, was produced. Simulations run with different numbers of personnel, different levels of culling efficacy, and different population growth rates, predicted that the UK ruddy duck population would fall below 50 birds between 2008 and 2012. The novel spreadsheet model presented here can easily be applied to a range of eradication schemes where limited data are available on population size and culling efficacy. This would allow funding bodies to have a greater degree of certainty about the cost and outcome of an eradication programme.