The Birders’ Dozen Profile 6: Wood Thrush
Welcome to the Birders’ Dozen! We’ve reached the halfway mark of the series, and in this and the next six issues we are going to continue introducing the bird species from Forestry for the Birds. The Birders’ Dozen are forest birds that can benefit from targeted management practices, as most are declining due to habitat loss. We’ve curated this list to cover a wide range of habitat types, from young to mature forest, open to closed canopy, or dense to non-existent shrub layers. Our goal is to engage landowners and foresters in the process of managing forests for wildlife, or “forests for the birds.”
Susceptible to habitat fragmentation and loss across both its breeding and wintering grounds, the Wood Thrush is a secretive migratory species with a big voice, and has become a poster child for forest management tools. The Wood Thrush is an interior forest resident, particularly of diverse habitats with a shady, open forest floor and decaying leaf litter for invertebrate foraging. Mature forest landscapes, rather than small isolated fragments, provide optimal protection from edge-specializing nest parasites such as Brown-headed Cowbirds. For landowners who don’t have large woods, improvement of small stands and edge-dominant habitats can also benefit Wood Thrush, especially during the migratory period.
Natural History
Wood Thrushes are mature forest specialists. More specifically, mature forests with moist floors and understory cover are consistently used by Wood Thrushes, as well as areas with large trees like beeches and maples for singing perches and production of leaf litter for foraging microhabitat. Thrushes eat primarily insects and fruits, so habitats that provide resources for insects and fruit-bearing shrubs are important. Nesting success is often determined by protection from predators, and larger forest areas (250 acres or more) have lower risk from predators like snakes, raccoons, and domestic cats.
Wood Thrushes nest in shrubs or young trees, usually in areas with denser shrubs than the surrounding forest. These small, brown birds are generally monogamous during the breeding season, though males and females often engage in mating outside their pair. Females are the primary nest-builder, though males can help. Nests are built in small trees or shrubs in clumps of vegetation to provide camouflage from predators. Thrushes will lay 3-4 small turquoise-green eggs, which the female incubates around 12-13 days before they hatch. Both parents feed invertebrates or fruit to the young, which fledge around two weeks after hatching.
Peak fall migration for Wood Thrushes in Indiana is generally around late August, while peak spring migration is generally mid-May. During migration, thrushes increase their consumption of high-fat fruits, since fat is the main energy source used to make the long flights necessary to reach wintering habitats. Like many birds in the Birders’ Dozen, the Wood Thrush spends the winter in Central America after flying non-stop across the Gulf of Mexico. These trans-Gulf flights are taxing on birds, requiring them to significantly increase their body mass through eating fatty fruits like spicebush and elderberry fruits.
Habitat Management
Despite dependence on large, mature forest patches, Wood Thrushes also use edge habitats during migration seasons, where high-fat fruit such as dogwood and elderberry are more abundant. Smaller patches that may be used less in the breeding season may still be used in other seasons or as overflow habitat from larger patches, and their management can still benefit Wood Thrush. In addition, habitat loss in wintering habitats in Central America has been identified as a possible reason for declining numbers of Wood Thrushes; support of conservation in Central America and agroforestry systems such as shade-grown coffee can further benefit both birds and people.
Wood Thrushes, like mentioned before, are mature forest specialists. They are best able to thrive in large areas of forest, and breeding in smaller patches is more difficult and less successful. One reason for this difficulty in reproduction is a bird we met last issue, the Brown-headed Cowbird. When Wood Thrushes are forced to breed in smaller patches and areas with more edge habitats, especially adjacent to lawns and pastures, they are more susceptible to cowbird parasitism. Cowbirds lay their eggs in a thrush’s nest and force the thrush to raise cowbird young as their own. Management strategies that encourage growth of large areas of mature forest can mitigate this problem to some degree.
Another aspect of management that can greatly benefit the Wood Thrush is a targeted invasive species removal plan. As mentioned earlier, Wood Thrushes need high-fat fruits, particularly during migration. Though invasive plants like bush honeysuckle produce fruits, these fruits are high in sugars and low in fats, making their nutritional value very low. Management plans that incorporate invasive species removal and encourage growth of native shrub patches can provide better sources of fuel for Wood Thrushes and many other migratory species, as well as providing areas for shelter and nesting.
Agroforestry—the intersection of crop production and forestry—can also provide a useful framework for Wood Thrush conservation. In the breeding range, bird-friendly maple syrup production can benefit Wood Thrushes, and shade-grown coffee crops in the wintering range, which leave the tropical forest canopy intact, can provide habitat as well. Audubon Vermont, the original inspiration for Forestry for the Birds, has produced a series of resources for bird-friendly maple forest management (cited under References), and Purdue Extension is also producing resources to help landowners improve their maple syrup production. In addition, consumers may be able to choose bird-friendly or shade-grown coffee, which encourages habitat for migratory birds as well as sustainable livelihoods for farmers.
Conclusion
This beautiful and vocal bird, adding its wood flute song to the forest symphony, is a favorite for many, and mature forest management can greatly benefit their declining populations. Encouraging growth of native shrubs in large forest tracts, leaving the forest canopy intact, and allowing a well-developed leaf litter layer to thrive can all encourage Wood Thrush breeding areas. In addition, some agroforestry techniques like shade-grown coffee in Central America and maple syrup production in the Midwest can also provide habitat for these charismatic birds, helping both birds and people to thrive.
Special thanks to the Alcoa Foundation, the Indiana Forestry Educational Foundation, and The Nature Conservancy for their support and leadership of Forestry for the Birds.
Jessica Outcalt was an independent consulting biologist who worked with The Nature Conservancy to develop the “Birders’ Dozen Profiles.” She is now an Agriculture and Natural Resources educator with Purdue Extension in Grant County. She completed her BS in biology at Taylor University, her PhD in wildlife ecology at Purdue University, and is passionate about birds and getting people involved in conservation and scientific processes.
References
Audubon Vermont. 2022. “Bird-friendly Maple Resources.” Accessed March 2022. https://vt.audubon.org/conservation/bird-friendly-maple-resources.
Bailey, Brett A., and David I. King. 2019. “Habitat Selection and Habitat Quality for Wintering Wood Thrushes in a Coffee Growing Region in Honduras.” Global Ecology and Conservation 20 (October): e00728. https://doi.org/10.1016/j.gecco.2019.e00728.
Bertin, Robert I. 1977. “Breeding Habitats of the Wood Thrush and Veery.” The Condor 79 (3): 303–11. https://doi.org/10.2307/1368007.
Brock, Kenneth J. Brock’s Birds of Indiana – Wood Thrush. Amos W. Butler Audubon Society, 2006.
Ellison, Jillian. Purdue University College of Agriculture. “Grant Aims to Bring Indiana Maple Syrup Industry Back to Its Former Glory.” News & Stories. Accessed March 2022. https://ag.purdue.edu/stories/indiana-maple-industry/.
Evans, Melissa, Elizabeth Gow, R. R. Roth, M. S. Johnson, and T. J. Underwood. 2020. “Wood Thrush (Hylocichla Mustelina).” Birds of the World, Accessed March 2020. https://birdsoftheworld.org/bow/species/woothr/cur/introduction.
Hoover, Jeffrey P., Margaret C. Brittingham, Laurie J. Goodrich, Effects of Forest Patch Size on Nesting Success of Wood Thrushes, The Auk, Volume 112, Issue 1, 1 January 1995, Pages 146–155, https://doi.org/10.2307/4088774