Fire created habitat partitioning and isolation between hybridizing warblers

Abstract

Hybridization or the breakdown of reproductive barriers has perplexed conservationists for centuries. Hybridization between the golden‐winged warbler (Vermivora chrysoptera) and blue‐winged warbler (Vermivora cyanoptera) has received extensive study across North America for more than a century and indicates widespread, bi‐directional genetic introgression. We found evidence fire is creating habitat conditions leading to isolation between nesting golden‐winged warblers and blue‐winged warblers. This effect is likely the result of fire's ability to promote grass cover and suppress woody plants, leading to habitat use partitioning between golden‐winged warblers and blue‐winged warblers. In addition to minimizing contact between the species, fire is creating habitat conditions on mixed sites that greatly favors golden‐winged warblers over blue‐winged warblers. Fire provides a plausible explanation for the original split in these sister species and its near elimination from eastern North America provides at least a partial explanation for the golden‐winged warbler's extensive range‐wide decline. Fire also provides a potential conservation tool by isolating golden‐winged warbler and blue‐winged warbler nesting populations. If nesting populations can be isolated, relatively rapid phenotypic sorting can be achieved, which could lead to a clearer distinction between the taxa as well as species preservation.