The warbler parents do not recognize that a cowbird chick in its nest is not its own, and so will naively care for the cowbirds. Cowbird chicks hatch a day before any warbler eggs, and are much larger than warbler chicks. Consequently, they get most of the food brought to the nest by warbler parents. Biologists believed that Kirtland's warbler was likely to become extinct if that rate of parasitism was allowed to continue. Events occurring during migration or at the bird's winter habitat also may be harmful.
Biologists know little about the warbler's Caribbean home.
Droughts and logging on the islands may have contributed to the decline of the warbler. Recent publications discuss possible correlations between heavy logging in the Northern Bahamas during the 1960s and 1970s and the warbler population decline between 1961 and 1971. Recovery of the Caribbean pine forest now coincides with improvements in the warbler population. The warbler migrates south during the hurricane season, storms may kill some of the birds. The warbler's diet of insects and vegetation may expose the birds to pesticides.