From: Martin on 26/06/2001 12:21 PM
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cc:
Subject: Mallard impacts (Vic.)
Michael M asks about the threat of the introduced Mallard on our native
waterfowl.
In Victoria this same item was nominated as a potentially threatening process
under the Flora and Fauna Guarantee Act in late 1990. At that time the
Scientific Advisory Committee (Vic.) assessed the nomination and decided that
the argument was not proven. The specific wording used in the Committee's Final
Recommendation Report is as follows:
'The nomination argues that the Pacific Black Duck Anas superciliosa and the
Chestnut Teal A. castanea are threatened with genetic swamping from
interbreeding and competition with the introduced Mallard Duck Anas
platyrhynchos.
The SAC is of the opinion that hybridisation with the Mallard is not a threat to
the Chestnut Teal. It may be a threat to Black Ducks in New Zealand, but there
is no clear evidence that the survival or evolutionary development of the Black
Duck is threatened in Victoria.
There may be more Mallard x Black Duck hybrids in existence than is realised, as
the morphological difference in the F1 generation can be subtle, especially if
the Mallard parent is of the domestic variety rather than the classic wild type
(additional expert opinion). Hybridisation between the Chestnut Teal and the
Mallard is well known in captivity but there are few records in the wild
(additional expert opinion). Very little work has been done on this issue.
Braithwaite & Miller (1975) believe that Mallard hybridisation is a not a threat
per se, but large numbers of Mallards in one area could pose a problem by
swamping the native species.
Evidence from Mexico and New Zealand (provided by the SAC) indicated that the
process is a problem only when there is a great population imbalance i.e. many
more Mallards than native species. In Victoria, native species outnumber the
introduced mallard, and have a wider range. There is evidence from New Zealand
that there is reduced egg hatch and infertile eggs from hybrid matings, and
there is reduced reproductive success in the first generation.'
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Note that the above conclusion does not mean a 'new' nomination for the
threatening process would not succeed in being listed in Victoria. It does,
however, acknowledge that there is a problem overseas.
I personally encourage caravan park owners and councils wherever I visit to
remove these birds like any other introduced avian pest. I have observed first
hand Mallards using their size and aggression against native waterfowl eg. Lake
Anderson at Chiltern in ne Victoria.
For anyone interested I am happy to send out a copy of the short SAC
Recommendation Report mentioned above. Please contact me directly with your
snail mail address.
cheers, Martin
Martin O'Brien
Executive Scientific Officer - Scientific Advisory Committee
Parks Flora and Fauna Division
Department of Natural Resources and Environment
4/250 Victoria Pde.,
East Melbourne 3002
AUSTRALIA
Tel: 9412 4567
Fax: 9412 4586
(prefixes: Interstate 03 International 613)
email:
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