The Semper's Warbler (Leucopeza semperi) is an extremely rare or possibly extinct New World Warbler which is endemic to Saint Lucia.
It is about 14,5 centimetres. The plumage of the adults is dark gray at the upperparts and greyish white at the underparts. The immatures are brownish-grey above and have buffish underparts. The long legs are pale yellow. It lives in the undergrowth of montane and elfin forests. The call consists of tuck-tick-tick-tuck noises. Nothing is known about its ecology but it is probably a ground-nesting bird.
It was rather abundant in the 19th century but there are only a few reports of this species in the 20th century. According to West Indian birdlife expert James Bond it was last collected on the summnit of Piton Flores in 1934, another report was from March 1947 where it was sighted between the Piton Lacombe and the Piton Canaries. The last reliable sighting was in 1961. Though unconfirmated sightings were in 1965, 1972, 1989, 1995 and 2003 there is a weak hope for a rediscovery because suitable habitat is still remain. Causes for its decline were probably introduced mongooses. Due to its possibly ground-nesting habits it was an easy prey for the mongooses. Another cause might be habitat destruction.