Brown Thrasher

Scientific Name	Toxostoma rufum
Survival Strategy	Short-distance migrant
Arrival in Upper Midwest	Mid-April to Mid-May
Departure	Early September to early October
Destination	Lower Ohio River Valley, Gulf Coast
Conservation Status	Least Concern

Phenology

Spring
Brown thrashers return to the upper Midwest in late April with pair formation and nest construction starting soon after. By early May, the female lays 3 to 4 eggs followed by 10 to 14 days of incubation, a task shared by both parents. Thrasher chicks remain in the nest until they fledge in 11 to 12 days.

Summer
Parents continue feeding their brood for 17 days after fledging.

Fall
The brown thrashers that breed in the Upper Midwest begin their journey to their winter range in early September to early October.

Winter
Most brown thrashers spend the winter along the Gulf Coast or in the Lower Ohio River Valley. A few individuals will attempt to over-winter in the upper Midwest, but survival is unlikely.

Behavior

Feeding Behavior
Thrashers forage on the ground by “thrashing” the grass and leaf litter with their beaks, then quickly seizing anything that looks edible before it can get away. Their strong beaks can pound open acorns and occasionally turn treefrogs, small snakes, and in one reported case, a hummingbird into a meal.

Territorial Behavior
A male thrasher will claim its territory by singing loudly to warn other thrashers to stay away. This aggressive bird will chase away any brown thrashers that ignore the melodious warning in both its summer and winter ranges. Any perceived predator will likely feel the wrath of the thrasher’s dagger-like bill, which has drawn blood from dogs, cats, and humans who have gotten too close to the thrasher’s nest.

Physiology

Piloerection
The weather in the winter range of the brown thrasher will occasionally mimic that of the Upper Midwest. Although the duration is shorter, the colder temperatures can become lethal. By fluffing their contour feathers (piloerection), the bird traps air, increasing the insulation value of its down feathers and reducing the number of calories needed to survive the cold.

Diet

Brown thrashers are omnivores, preferring insects for their summer diet and adding fruits, seeds, and acorns in their winter range. Not willing to pass up an easy meal, brown thrashers will eat an occasional lizard, small snake, or treefrog.

Lifespan and Mortality

The average life expectancy of a brown thrasher is about three years. By using banding data, researchers found that several thrashers reached at least 12 years. Only 35% of brown thrasher nestlings survive their first or second year of life. Thrashers surviving the perils of youth have a 75% survival rate as adults.

Predators
Nest predators include gray catbirds and many species of snakes. Brown thrashers will sometimes build their nest on the ground, which increases the potential for predation from skunks and domestic cats. Adult thrashers are prey for peregrine falcons.

Agricultural insecticide application has a lethal impact on insectivores like the brown thrasher. Disease, parasites, and cold temperatures can also be fatal. In January 1977, arctic weather in southern Illinois dropped temperatures to -28°C (-18°F) and reduced the population of brown thrashers by more than 80%.

Climate Vulnerability

The brown thrasher’s range would shift north and become significantly smaller in a warming climate, and the state bird of Georgia would no longer be found in Georgia.

Never Stop Learning

Brown thrashers mimic the songs of other birds, typically singing each phrase twice. One study found that they could reproduce more than 1000 different song types.

References

Cavitt, J. F. and C. A. Haas (2020). Brown Thrasher (Toxostoma rufum), version 1.0. In Birds of the World (A. F. Poole, Editor). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bow.brnthr.01

Cutright, Harriman, B. R., & Howe, R. W. (2006). Atlas of the breeding birds of Wisconsin / editors, Noel J. Cutright, Bettie R. Harriman, Robert W. Howe. Wisconsin Society for Ornithology, Inc.

How Climate Change Will Reshape the Range of the Brown Thrasher https://www.audubon.org/field-guide/bird/brown-thrasherCutright, Harriman, B. R., & Howe, R. W. (2006). Atlas of the breeding birds of Wisconsin / editors, Noel J. Cutright, Bettie R. Harriman, Robert W. Howe. Wisconsin Society for Ornithology, Inc.

Gray, P. 2007. “Toxostoma rufum” (On-line), Animal Diversity Web. Accessed November 23, 2021 at https://animaldiversity.org/accounts/Toxostoma_rufum/

How Blizzards and Extreme Cold Impact Birds https://blog.nature.org/science/2017/02/13/how-blizzards-and-extreme-cold-impact-birds/

Kreitinger, K., Y. Steele and A. Paulios, editors. 2013. The Wisconsin All-bird Conservation Plan, Version 2.0. Wisconsin Bird Conservation Initiative. Wisconsin Department of Natural Resources. Madison, WI. http://www.wisconsinbirds.org/plan/species/brth.htm