Somebody's been feathering their nest with an irreplaceable English archive of rare tropical birds.

Curators of the Natural History Museum at Tring, 30 miles northwest of London, said Thursday that thieves have stolen about 300 of their most gloriously hued specimens from a vast collection assembled over centuries.

They discovered the carefully researched thefts in June but couldn't be certain when the raid actualy happened.

The museum's science director, Richard Lane, said the specimens taken included particularly colorful species from South America and Papua New Guinea. The specimens had been "painstakingly assembled" and were impossible to replace, he said.

"It is very distressing that we should have been deliberately targeted in this manner," he said.

Detectives appealed to bird collectors to keep an eye out for anyone trying to sell unusual bird skins.

"This is a very unusual crime," said Det. Fraser Wylie of the Hertfordshire Constabulary. "We are keen to recover the bird skins, which are part of a national heritage."

He said the thieves could have been working on behalf of a collector or planning to use the birds' plumage to make fishing lures, dresses or costume jewelry.

Curators emphasized that the raiders didn't touch any of the museum's approximately 8,000 birds collected by Charles Darwin when the 19th century naturalist was developing his theory of evolution.