Threats to Wood Thrush survival and nesting success increase considerably when roads, energy development, and urbanization fragment large patches of forest. On the edges of fragmented habitat, acid precipitation has a greater impact on this species by depleting invertebrate prey compared to individuals nesting in the forest interior. Similarly, Brown-headed Cowbird (Molothrus ater) nest parasitism significantly lowers nesting success in edge habitats. Female cowbirds lay their eggs in the nests of other songbirds, including the Wood Thrush. Cowbird eggs typically hatch sooner and the faster-growing cowbird nestling will often push other nestlings out of the nest and demand more food. The loss of large tracts of mature forests has lead Wood Thrush to more frequently inhabit secondary forest, where understory is not as dense, leading to higher predation rates from small mammals. Changes in forest structure and composition, owing to forest management and species interactions (e.g., overbrowsing by white-tailed deer), are frequently implicated in Wood Thrush Declines.
Furthermore, the population declines experienced in their breeding range is coupled with destruction of habitat in Central American wintering grounds. Loss of primary forests in the tropics may force birds into secondary habitats where they may have higher winter mortality rates and lowered fitness, which could weaken their ability to migrate and breed successfully. The secondary effects of forest loss on the wintering grounds are less clear, but it seems likely that rapid conversion of forest to agriculture is creating great habitat loss, which likely increases mortality and decreases overall fitness.