NEW GENUS AND SPECIES OF FURNARIID (AVES, FURNARIIDAE) FROM THE COCOA-GROWING REGION OF SOUTHEASTERN BAHIA, BRAZIL

We here describe Acrobatornis fonsecai, a new genus and species in the Furnariidae, from the Atlantic Forest of southeastern Bahia, Brazil. Among the outstanding features of this small, arboreal form are: black -and-gray definitive plumage lacking any rufous; juvenal plumage marke dly different from adult; stout, bright-pink legs and feet; and its ac robatic foraging behavior involving almost constant inverted hangs on foliage and scansorial creeping along the undersides of canopy limbs. Analysis of morphology, vocalizations, and behavior suggest to us a ph ylogenetic position close to Asthenes and Cranioleuca; in some respect s, it appears close to the equally obscure Xenerpestes and Metopothrix . New data on the morphology, vocalizations, and behavior of several f urnariids possibly related to Acrobatornis are presented in the contex t of intrafamilial relationships. We theorize that Acrobatornis could have colonized its current range during an ancient period of continent al semiaridity that promoted the expansion of stick-nesting prototypes from a southern, Chaco-Patagonian/Pantanal center, and today represen ts a relict that survived by adapting to build its stick-nest in the r elatively dry, open, canopy of leguminaceous trees of the contemporary humid forest in southeastern Bahia. Another theory of origin places e mphasis on the fact that the closest relatives of practically all (if not all) other birds syntopic with Acrobatornis are of primarily Amazo nian distribution. Acrobatornis fonsecai has a most unusual distributi on in a restricted region in which lowland Atlantic Forest has been co nverted virtually entirely to cocoa plantations. Until very recently a lucrative and vitally important source of income for Bahia, the econo mic base for cocoa production has suffered catastrophic, apparently ir recoverable, decline owing to ''witch's broom'' disease, which has pro ven resistant to all forms of control. The predictable wave to cut and sell the tall trees shading failing cocoa plantations has already beg un in earnest with the consequence that the remnant forest canopies in this region, upon which Acrobatornis fonsecai is totally dependent, a re being rapidly destroyed. This remarkable new furnariid and the secr ets it holds for elucidation of phylogeny, evolutionary history, speci ation patterns, and zoogeography, if not safeguarded immediately, when its habitat is still for sale, could disappear in the coming decade.