Zoologists test fidelity of Albert Park swans
[ Research Review 0307 : ]
By Rebecca Scott
The mating habits of Albert Park’s black swans have been under high-tech scrutiny from researchers at the University of Melbourne.
A research team led by Dr Raoul Mulder from the University’s Department of Zoology has been capturing and tagging the swans that live around the lake as part of a long-term study investigating the iconic birds.
“Swans have long been renowned as symbols of lifelong fidelity and devotion, but our recent work has shown that infidelity is rife among black swans,” said Dr Mulder.
DNA paternity analysis has revealed that about one in six cygnets are ‘illegitimate’, resulting from covert matings between a female swan and a male other than her own partner.
“In this study we want to try to understand why the birds are sometimes unfaithful to their partners, and what tactics are used by males and females to influence the outcome of paternity,” said Dr Mulder.
Studies have shown that the chances of a male gaining paternity depend on a complex range of factors, including the frequency, timing and order of matings. But the often secretive mating habits of birds have proven difficult or impossible to monitor in the wild. This is where the project’s innovative technology comes in.
Dr Mulder said each swan has been captured, measured and fitted with a uniquely numbered leg band before being released back onto the lake. This is a routine procedure employed in bird studies, which enables researchers to identify individual birds, track their movements and determine their eventual fate.
“However, each of the males at Albert Park will also have a tiny microchip attached to one of its tail feathers,” said Dr Mulder.
“The microchips are identical to those implanted in domestic pets for identification, but their purpose in this study will be to record the mating behaviour of the birds.”
During the breeding season, females will be temporarily fitted with a miniature state-of-the-art electronic tracking device, or ‘decoder’. The devices look like small backpacks and are placed on the bird’s lower back. They are usually undetectable under the folded wings, and have been extensively trialed to ensure that they have no harmful effects on the birds.
Dr Mulder explained that “When a male and female copulate, the female’s decoder unit detects the microchip implanted in the male’s tail feathers, registering the male’s identity, as well as the time of copulation.
“All mating events are logged onto the decoder unit, so that a complete record of her mating behaviour over several weeks can be downloaded onto a computer when the swan is recaptured,” Dr Mulder said. “This information can then be related to the outcome of paternity of the cygnets, which we determine using DNA markers.”
The earlier findings about mating fidelity came from a study that Dr Mulder and his colleagues have conducted at Lake Wendouree in Ballarat since 1999 with the help of local field naturalists. More than 800 swans have been individually tagged and monitored.
The new study at Albert Park Lake is funded by a grant from the Australian Research Council, and with permission from Parks Victoria, the Department of Sustainability and Environment, the Australian Bird and Bat Banding Scheme and the University of Melbourne’s Animal Experimentation Ethics Committee.
Researchers commenced their work in May last year. Although initially the grant will provide funding for three years, the researchers hope to monitor the swan population over a longer term.
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