New realms of research into the habits of birds of prey have been opened up by scientists using the latest developments in DNA fingerprinting.

"Micro-satellite DNA fingerprinting" is enabling scientists to check DNA using such a small sample of tissue that it can be found in a human's used coffee cup - or a bird's feather. Nottingham University geneticists are exploring using it to track birds by removing and analysing feathers from their nests rather than having to catch them.

"It's very difficult to catch a peregrine falcon that's nesting up a cliff face," said David Parkin, reader in avian genetics at Nottingham University. "You can climb up to the nest if you know what you are doing, but hanging around to catch it is another matter." By removing a feather and testing the DNA, however, progress can now be made in answering questions such as whether the same birds return to the nest every year; what their mating patterns are and how many offspring they have.

The technique will also help to prevent the international illegal trade in rare birds. All such birds that are kept captive must be registered. The scientists hope to catch people who illegally steal eggs from the nests of birds of prey and register the birds as offspring of their own, captive ones.

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Normal DNA fingerprinting compares two stretches of chromosome to see how similar they are. Dr Parkin and his colleagues have already helped convict six illegal bird-keepers using this method, by taking blood samples and comparing them with the blood of the birds whom the keeper claims are the parents. But the method requires a registered vet to take the blood sample.

Micro-satellite DNA fingerprinting is a version of the conventional method. It works by slicing out a much smaller "satellite" of the chromosome, perhaps a piece of only two bases which are repeated three times. "If one of a father's chromosomes carried three repeats and the other carried ten repeats then half the children would have three, and half would have ten repeats," said Dr Parkin.

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Micro-sequencing is useful because of a paradox. Scientists are looking at such small satellites that they cannot be analysed themselves. Instead they are amplified using the "polymerise chain reaction". But this reaction can only be done on very small sequences.

So previously, when larger satellites were studied, the amplification reaction could not be used and scientists had to collect enough of the sample to study it in the raw without the benefit of magnifying reaction.

Dr Parkin believes that the blood sample technique has already resulted in a drop in illegal trade.