YET more evidence has emerged of researchers inadvertently harming the animals they study in the wild.
The results suggest that radio-collars used to track water voles have had a drastic effect on the sex ratio of their offspring, skewing it towards males. Previous studies have found that tagging penguin wings and clipping amphibians鈥� toes to identify individuals harm the animals鈥� survival chances (快猫短视频, 7 August 2004, p 15).
Tom Moorhouse and David MacDonald at the University of Oxford made the latest discovery by accident, while studying two populations of water vole (Arvicola terrestris). In the first two years they laid traps for the animals, but in the third they switched to radio tracking at one of their sites. This involves attaching a 4.5-gram collar with a 10-centimetre antenna to the animals.
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Females fitted with the collar produced nearly five times as many male offspring as female, they found. By contrast, the sex ratio of offspring in trapped animals was even (Journal of Applied Ecology, vol 42, p 91).
Because the study was not designed to look at this effect, the pair say they can only speculate about how the collars might cause the change. But a rise in the proportion of male offspring is associated with stress in breeding female water voles. 鈥淩esearchers must actively look for such effects in any studies we do,鈥� says Moorhouse.
