Bachman’s Warbler – The world’s Rarest Warbler
The only Bachman’s warbler (Vermivora bachmanii) seen in 1986 was in Cuba and no more than six birds have been recorded anywhere since the 1950s. The former range was from southern Indiana and southern Missouri east to Virginia, south to northern Arkansas and Alabama. Nests have been found in just five states and the winter quarters are in Cuba and perhaps the Isla de Pinos, Bahamas.
Bachman’s Warbler Breeding and Habitat
The favored habitat of Bachman’s Warbler is mature swamp woodland, and breeding is in marginal thickets, mainly cane. Enough breeding habitat still exists to support a healthy population so the most likely cause of significant decline must be the destruction of the species’ winter habitat.
The main reason for the extinction of Warblers
Most of the world’s warblers are very numerous. For example, the autumn population of the willow warbler has been estimated at 1,000 million birds, making it the most abundant of the Palearctic passerines which winter in Africa.
However, a few island endemics are particularly vulnerable, including the Aldabran brush warbler (Nesillas aldabranus), which was down to 11 individuals in 1983.
Another American species which has entered a severe decline is Kirtland’s warbler (Dendroica kirtlandii). This larger bird has one of the most restricted breeding ranges of non-insular birds and nests only in an area of about 100 x 130 km (62 x 80 miles) in lower northern Michigan. Even within this small area it is confined to woods of jack pine 8—22 years old and m (3—19.5 ft) high. In winter it is confined to the Bahamas and adjacent Turks and Caicos Islands.
The main threat to the Kirtland’s warbler was, for once, a natural one — the sudden spread of the parasitic brown-headed cowbird (Molothus ater) against which it has no defenses. The cowbirds were trapped and removed and the threat receded, but the habitat requirements are still not secure and the Kirtland’s population is only 400—450 birds.