Further to Bills mention of potential negative interactions between the
introduced Mallard and Pacific Black Ducks. I offer some interseting
information for the list.
Hybridisation by the introduced Mallard was nominated for listing as a
threatening process under the Flora and Fauna Guarantee Act in 1990. The
Scientific Advisory Comittee (SAC) assessed the nomination but rejected it
at the time. In its Final Recommendation Report on this item the Committee
had the following (in part) to say:
'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.'
Background Information:
- 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.
- Hybridisation between the Chestnut Teal and the Mallard is well known in
captivity but there are few records in the wild. 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 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.
~~~~~~~~~
Copies of the short Recommendation Report are available to interested
parties. Provide me with a Australia Post address and I can forward them.
cheers
Martin O'Brien
Executive Scientific Officer, Scientific Advisory Committee
Department of Sustainability and Environment
4/250 Victoria Pde., East Melbourne 3002
Tel: 9412 4567 Fax: 9412 4586
(prefixes: Interstate 03 International 613)
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