Thor was created by artificially inseminating his mother with frozen sperm. What is more, the chick was not the product of some laboratory experiment; he was created on a sheep farm in South Lanarkshire by falconer and eagle breeder Andrew Knowles-Brown, with the help of Graham Wishart, a biologist at the University of Abertay, Dundee, and a bird reproduction expert.

Sperm from Tallin, a golden eagle, was slowly frozen by placing the samples in an insulated box that could be kept in a domestic freezer. It was then immersed in liquid nitrogen. Meg, a female Steppe eagle, came into season in March, and Mr Knowles-Brown defrosted the sperm and inseminated her with a syringe. Because of foot and mouth precautions, Mr Knowles-Brown and Mr Wishart were unable to meet on the farm, so they arranged a rendezvous at a motorway service station where Mr Wishart handed over the chemicals, simplified slow-freeze equipment and detailed protocols.

Thor’s hatching showed that sophisticated techniques could be mastered by non scientists to preserve rare birds of prey; Mr Knowles-Brown hopes that artificial insemination using frozen sperm might help to build up populations of other endangered birds. As the techniques are refined and adaptd, advocates of modern reproductive science are considering more radical strategies, following in the footsteps of Dolly, the cloned sheep.

A few months ago, a rare type of Asian ox called a gaur was born at a farm in the United States. Noah lived a few days before falling victim to a common, deadly infection. The experiment was judged a breakthrough, however, as the gaur was a clone, created by putting the nucleus of a single skin cell from a male gaur that had died eight years earlier into the egg of an ordinary cow, which acted as a surrogate mother. Now the scientists involved are planning an even more ambitious project: to bring an extinct animal back from beyond the grave. The last known bucardo, a Pyrenean mountain goat, died last year after being hit by a falling tree, but its DNA was recovered and has been frozen awaiting a cloning operation.

In India, scientists want to clone the rapidly declining Asiatic cheetah, using a leopard as a surrogate mother. Chinese experts are trying to do the same with the panda, but are being hampered by the lack of an appropriate close relative. And Korean teams want to bring back the Amur tiger.

Yet such animals might be doomed to a miserable existence as exotic exhibits in zoos. Many are extinct or have become endangered because man destroyed their habitats. Perhaps it might be smarter to preserve, even restore, these before bringing back their former inhabitants.

Weblinks cloned gaurs and bucardoswww.somafound.org San Diego Frozen Zoo www.sandiegozoo.comconservationfrozen.html

Photograph by Alan Richardson