Acid rain threatening songbirds

Acid rain is contributing to declining songbird populations, say scientists.

A study of the breeding patterns of North American wood thrushes since 1966 in the eastern United States has found that its decline over the past 30 years can be closely correlated with levels of the atmospheric pollution acid rain.

The scientists, led by Ralph Hames of Cornell University in Ithaca, New York, said that acid rain might affect calcium levels in the soil and so weaken the ability of birds to make strong shells for their eggs.

Low calcium might also affect the populations of soil-dwelling animals that birds live on, or increase the risk of poisoning through the uptake of other substances that can replace calcium in the diet.

There has been a similar decline in songbirds in Britain, mostly linked to changes in farming practices. The latest findings, published in the Proceedings of the National Academy of Sciences, suggest acid rain could also be a factor.