Mallard x Pacific Black Duck hybrids commonly occur on Lord Howe Island in areas of high public use in fresh, estuarine and saline water, particularly where there is abundant mown or grazed grass and where feeding occurs.
Observations of phenotype characteristics suggests that introduced Mallards are dominant and suppressing the native Pacific Black Duck, with 81% of birds classified as Mallards or Mallard-like hybrids, 17% as intermediate hybrids and only 2% as Pacific black-like hybrids. No pure Pacific Black Duck were observed. The existing population is also likely to continue to suppress new arrivals of Pacific Black Duck.
These hybrid species pose obvious direct and indirect economic, social and environmental impacts to Lord Howe Island. Impacts include the suppression of native Pacific Black Duck and unquantified negative social and economic impacts to aesthetics, natural values and tourism. They also play an unquantified role in the maintenance of avian influenza and other viruses potentially important for the wellbeing of endemic fauna and human health. Ducks are a known reservoir of influenza viruses, are more likely to carry these viruses than any other species on the island, and have a high degree of contact with humans.
A management program using trapping, shooting and opportunistic capture by hand was conducted for five days in October 2007. Standardised indices of duck abundance before and after management indicates that the duck population was reduced by 71.7% during this time, and that 28 (SE=3.3) remained after management. The majority of ducks were removed by shooting. Hand capture was most efficient but was opportunistic and limited to juveniles and chicks. Trapping was the next most efficient technique but had difficulties with disturbance by the public.
Eradication is feasible and a program of monitoring, shooting and targeted poisoning using alpha-chloralose is recommended. Reintroductions following eradication are likely to occur and ongoing management will be necessary to prevent re-establishment.
|Author||John Tracey, Brian Lukins and Chris Haselden|
|Secondary Author||Kerryn Molloy|
|Secondary title||A report to the World Heritage Unit, Lord Howe Island Board|
|Publisher||Invasive Animals CRC|
|Institution||Invasive Animals Cooperative Research Centre|
|ISBN/ISSN||ISBN: 978-0-9804999-0-2 (online)|
|Documents||Lord Howe Island Ducks report