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Chernobyl-based birds avoid radioactive nests

Birds in Chernobyl choose to nest in sites with lower levels of background radioactivity, researchers discover, but how they can tell remains a mystery.

Anders Mшller at Pierre and Marie Curie University in Paris, France, and Tim Mousseau at the University of South Carolina in Columbia, US, erected more than 200 nest boxes in the Red Forest, about 3 kilometres away from the nuclear reactor that exploded in 1986.

Using these artificial nests, they studied at the nesting habits of two species of birds – the great tit Parus major and the pied flycatcher Ficedula hypoleuca – between 2002 and 2003.

Moller and Mousseau wanted to see if either species would differentiate between nesting sites that had high and low levels of background radioactivity. The patchy distribution of background radioactivity in the area (due to the fact that radioactive material from the explosion did not settle uniformly) meant the nest boxes could be in very similar locations, with similar food supplies, but have widely varying levels of background radioactivity. Levels at some nest sites were as much as 2000 times natural levels elsewhere in the world.

Deformed sperm

The researchers found that both species had a definite preference for nest boxes with low radioactivity, with the pied flycatcher seemingly more sensitive than the great tit (see chart, bottom right).

Previous research done by Mousseau and colleagues (Trends in Ecology and Evolution, DOI: 10.1016/j.tree.2006.01.008) showed that higher radioactivity results in lower levels of antioxidants and also deformed sperm in barn swallows around Chernobyl. It therefore makes sense for birds to avoid more radioactive sites.

"It is not entirely clear exactly how the birds are able to tell which boxes are most contaminated", says Mousseau, adding that determining this will be very difficult without experimental manipulations.

Wildlife boom

A spokesperson for the Royal Society for the Protection of Birds told New Scientist that the study is interesting, but points out the unexpected benefits of the Chernobyl explosion. Reports show that the large human exclusion zone around the site has led to a boom in animal populations, including eagles, wolves and bears.

"Whatever effect the radioactivity is having, it seems to be less of a threat than human activities, such as agriculture," said the spokesperson.

"There have been few rigorous scientific analyses of background radiation and the natural abundance of species," responds Mousseau. "But every rock we turn over, every survey we do, we find some previously unreported effect of background radiation."

Immigrant influx

Mousseau believes that the reports of sustained animal populations around Chernobyl mask fluctuations within the populations.

He says studies he has carried out looking at where the barn swallow populations in Chernobyl come from suggest that "the populations are mostly sustained by immigrant birds", rather than birds returning to their nesting sites as they normally would.

So an overall picture showing constant population size could hide the fact that the local population is dwindling but being constantly replenished by neighbouring ones.

Journal reference: Proceedings of the Royal Society: B (DOI: 10.1098/rspb.2007.0005)

Автор: 
environment.newscientist.com

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