They were found to be missing following a break-in on Wednesday June 24.

The specimens stolen comprise a number of brightly-coloured tropical birds, some of which are uncommon in collections and, therefore, of special scientific concern. The Museum is working with the police and the Wildlife Crime Unit on the matter.

Professor Richard Lane, Director of Science at the Natural History Museum, commented 'The birds that were stolen formed part of the nation's natural history collection, painstakingly assembled over the last 350 years. The 70 million specimens looked after by the Natural History Museum are a resource of international importance in the development of scientific knowledge. Our ornithological collections are amongst our most heavily used and are consulted by researchers throughout the world, who either visit Tring or request loans from us. The knowledge gleaned from these collections can help protect endangered species and answer questions about the biodiversity of the world around us.

'It is very distressing that we should have been deliberately targeted in this manner. We take the security of our collections extremely seriously and are working closely with our internal security team and the police in thoroughly investigating this incident. Our utmost priority is working with the police to recover these specimens to the national collections so that they can be used by future generations of scientists'.

Detective Inspector Fraser Wylie, investigating from Hertfordshire Constabulary, said: 'This is a very unusual crime and we are keen to recover the bird skins, which are part of a national heritage, as well as of course apprehend those responsible for their disappearance. We are appealing for anyone who may have seen any suspicious activity around the museum in the time around when the break-in was, before it or subsequently. Also, we would ask any collectors of such specimens to keep a watchful eye out in case they are offered anything resembling them.'

The ornithological collections of the Natural History Museum are among the largest and most comprehensive in the world.

Anyone with any information on this crime should ring DI Wylie on 0845 33 00 222, citing crime reference number D3/09/450. Alternatively, call Crimestoppers anonymously on 0800 555111.