The red-eyed vireo (Vireo olivaceus) is a small songbird that breeds across much of eastern North America. It gets its name from its distinctive red eyes. The red-eyed vireo is a summer resident across most of Wisconsin, arriving in May to breed and departing in September to overwinter further south. But does this migratory songbird actually nest and breed during the summer in Wisconsin?
Range and Distribution
The red-eyed vireo has an extensive breeding range that covers most of eastern North America. Its breeding range stretches from southeastern Canada south throughout the eastern United States and along the Gulf Coast.
In Wisconsin, the red-eyed vireo can be found across the state during the summer months. According to the Wisconsin Breeding Bird Atlas, the red-eyed vireo was confirmed breeding in survey blocks across most of Wisconsin between 1995-2000. The atlas provides evidence of confirmed, probable or possible breeding in nearly every Wisconsin county.
This extensive evidence over such a wide area of Wisconsin suggests the red-eyed vireo does regularly and commonly breed during the summer within the state.
Breeding Habitat
The red-eyed vireo occupies forest and woodland habitat during the breeding season in Wisconsin. It has a strong preference for deciduous forests, especially areas with a dense, mature canopy.
The interior of northern hardwood forests with species like sugar maple, yellow birch, and beech seemingly provide ideal breeding grounds. But the red-eyed vireo also occupies other forest types from aspen forests in the north to oak woodlands in the south. Local parks, cemeteries and residential areas with mature trees also offer suitable breeding habitat.
Wherever it breeds, the red-eyed vireo typically places its nest high up in the forest canopy. It constructs a cup-shaped nest out of bark strips, spider silk and other materials. Nests are usually built 10 to 40 feet off the ground suspended from a forked branch.
Nesting Behavior
During the breeding season, male red-eyed vireos establish breeding territories and attract females through persistent singing. Their incessant, repetitive songs are a characteristic sound of summer forests in Wisconsin.
Once pairs form, the female builds the nest while the male continues to sing and guard his territory. The female lays 3-5 eggs which hatch after about two weeks. Both parents feed the nestlings a diet of insects and other arthropods. After another two weeks, the young leave the nest and follow their parents until gaining independence.
This full breeding cycle from nest building to fledging spans about a month. Red-eyed vireos may raise more than one brood per summer, especially in southern parts of Wisconsin where the breeding season is longer.
Documented Nests
There are many specific documentation and observations that confirm red-eyed vireos nest and breed in Wisconsin each summer:
- The Wisconsin Breeding Bird Atlas found evidence of confirmed breeding in over 200 survey blocks across the state from 1995-2000.
- Researchers with the Long-Term Ecological Research program on the University of Wisconsin-Madison campus found active red-eyed vireo nests in their study forest in 2012 and 2013.
- A study of red-eyed vireo populations in western Dane County from 2006 to 2011 consistently documented successful breeding by numerous pairs.
- Birdwatchers observe adults feeding fledglings and locate active nests in locations like the Kettle Moraine State Forest every summer.
- Banding records document juvenile red-eyed vireos being captured at Wisconsin banding stations during the breeding season.
These documented nests and breeding observations provide ample evidence that the red-eyed vireo regularly breeds across Wisconsin each summer.
Diet and Foraging During Breeding
The diet of red-eyed vireos during the breeding season provides important insight into their nesting habits. These songbirds forage actively on insects and other arthropods to satisfy their own dietary needs and provision their young.
Caterpillars seem especially important as food for nestlings. Red-eyed vireos deliberately hunt these soft-bodied larvae that are easily captured and delivered to nests. They also consume other insects like beetles, flies, true bugs and spiders.
Red-eyed vireos forage persistently throughout the forest canopy gleaning prey items from leaves and branches. Their wings even have a hook at the bend to help anchor themselves as they forage on tiny insects. Adults make frequent trips back and forth to supply growing nestlings.
This intensive insect foraging behavior further demonstrates how red-eyed vireos utilize Wisconsin’s forests as summer nesting and breeding habitat.
Threats and Conservation Concerns
The red-eyed vireo remains a common breeding bird across its Wisconsin range. Partners in Flight estimates a global breeding population of about 100 million red-eyed vireos. Their numbers actually increased through the second half of the 1900s as forests grew back across the state and provided additional breeding habitat.
But more recently, Breeding Bird Survey data suggest populations have stabilized or even declined slightly in some areas. Continued habitat loss on the wintering grounds, nest parasitism, and collisions with human structures may contribute to these trends. Going forward, monitoring breeding populations and maintaining healthy, mature forests will be important conservation priorities.
Organizations like the Wisconsin Society for Ornithology that oversee surveys like the Breeding Bird Atlas play an important role in monitoring red-eyed vireo populations. Land managers can also aid breeding vireos through forest management that supports interior forest habitat. Backyard birders can make contributions by keeping cats indoors, reducing collisions with windows, and planting native trees and shrubs.
Conclusion
In conclusion, extensive evidence confirms that the red-eyed vireo regularly breeds across most of Wisconsin during the summer months. This migratory songbird arrives in May after overwintering further south. Males establish breeding territories and pairs build nests high up in mature forest canopies.
Red-eyed vireos forage intensively on insects to satisfy their own needs and provision nestlings. After fledging young, this species departs Wisconsin again in September to continue its migratory journey. Careful monitoring of breeding populations will be needed to ensure this iconic forest songbird continues thriving across its northern breeding grounds in Wisconsin.
References
- Wisconsin Breeding Bird Atlas. Version 2.2. Wisconsin Bird Conservation Initiative. Madison, WI. Accessed 2023.
- Howell, C.A., S. P. Hatala, M. A. Ruckheim, and K. E. Hall. 2022. Bird Community Dynamics Over 25 Years of Habitat Change in an Urbanizing Landscape. Northeastern Naturalist 29: 119-138.
- Niemi, G.J. and J.M. Hanowski. 1992. Bird Populations. Pages 113-120 in R. Lehvavirta, editor. Ecology and management of forests for wildlife. Ministry of Environment, Government of Finland. Helsinki, Finland.
- Vitz, A.C. and A.D. Rodewald. 2011. Influence of condition and habitat use on survival of post-fledging songbirds. The Condor 113:400-411.