sean
Downsizer Moderator
Joined: 28 Oct 2004
Posts: 42219
Location: North Devon
|
 Posted: Mon Mar 21, 05 1:06 pm Post subject: Water voles |
 
|
Scientists investigating demise of the water vole are to blame for its decline
By Steve Connor, Science Editor
21 March 2005
Scientists studying the demise of the water vole have discovered that their own research technique is unwittingly contributing to the decline.
A study has found that tiny radio transmitters used by zoologists to monitor the movements of water voles in the wild appear to skew the sex ratio in favour of males to the disadvantage of females.
The findings will cause consternation among field biologists who have been taught that the radio tracking of wild animals has little or no effect on the survival of those individuals carrying the transmitters.
The research results also come at an important moment because the water vole, immortalised as "Ratty" in Kenneth Grahame's novel The Wind in the Willows, is on the verge of being officially listed as a protected species. A review of the Wildlife and Countryside Act 1981 by the Joint Nature Conservation Council has proposed that the water vole should be added to the list of protected species, which would make killing it in the wild illegal.
Water voles - often mistaken for brown rats - live along river banks and, although their habitat is protected, they are not. Their numbers have fallen from an estimated seven million in 1989 to fewer than 900,000 in 1996.
Habitat loss and the rise of the predatory American mink, which escaped from fur farms to establish a thriving wild population, are believed to be the main causes of the rapid decline. Nevertheless, the zoologists Tom Moorhouse and David MacDonald of Oxford University have found radio-tracking - used ubiquitously in the study of wild animals - can also have an impact if not used with care.
They compared two populations of water voles at two sites, one in Norfolk and another in Wiltshire, to see if radio transmitters attached to collars fixed around the necks of the animals had any effect on the wild population. In their study, which has been published in the current issue of the Journal of Applied Ecology, they found that females suffered a catastrophic decline when subjected to radio tracking.
"Several studies of rodent populations, including water voles, have reported no direct impacts of radio-collaring," Dr Moorhouse said. "In our study, however, we observed a rapid decline in the number of females present in one of our populations. This led us to consider the possibility that radio-tracking influenced the number of females at this site, potentially by affecting sex ratios of juveniles entering the breeding population."
Radio collars weigh only 4.5g, less than 2.5 per cent of a vole's typical body weight. They have deliberately smooth surfaces and the collars are designed not to tighten around the animal's neck, restrict its head movements or restrain it from using its riverbank burrows.
Dr Moorhouse said that radio transmitters played a critical role in understanding the natural behaviour of water voles, which can help their conservation. "We're not saying that radio tracking is a bad thing, but this is a timely reminder that we must be aware of, and monitor for, any potentially adverse effects of any monitoring technique," he said.
Females with radio collars show no physical signs of ill health. However, the scientists suggest that they may come under some kind of unexplained stress, causing them to produce a greater proportion of male offspring than females.
When the scientists compared a population of tagged voles with one that was untagged, they found that over three years there were nearly five times as many young males as females in the tagged group, whereas the sex ratio of youngsters remained constant at about 50:50 in the untagged.
"Our analysis revealed that the most likely cause for the female decline was a shift in the sex ratio of young raised by radio-collared females. This has implications for conservation research," Dr Moorhouse said. |
|
View Latest Posts