Tailing dirt

two of Europe's most attractive birds -- the blue tits and the great tits -- could play an important role in assessing the menace of air pollution. Tom Dauwe and his colleagues from the Belgium-based University of Antwerp have found that levels of heavy metals in the tail feathers of these birds provide a good picture of the levels of pollution around areas where they nest.

Dauwe and his colleagues analysed tail feathers of 32 great tits and eight blue tits caught from an area polluted by emissions of lead, cadmium, copper and zinc. During their analysis the researchers found that the birds' feathers had picked up much higher concentrations of the metals than feathers from 50 great tits and 10 blue tits caught from unpolluted areas. Lead concentrations, for example, were four times higher in the feathers from great tits caught from the polluted site. The researchers also studied some dead birds. They found a direct correlation between the amount of metals found in their feathers and the levels in their liver, kidney and muscle tissues.

According to Dauwe, the birds can be used by common people to keep tab on pollution -- a process which otherwise is very costly. The birds are easy to catch. Their feathers come out easily and the birds are not stressed by it. Moreover, using the birds' feathers is better than taking their blood sample. "Metal concentrations in feathers can be higher and hence easier to detect and quantify, than the metals in blood or tissue samples," explains Dauwe. Furthermore, tits seldom stray far from their nest, therefore, they can produce a reliable measure of pollution levels, especially for small areas.

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