The Red-eyed Vireo (Vireo olivaceus) is a small songbird found throughout eastern North America. With its distinctive red eyes and monotonous song, the Red-eyed Vireo is a familiar sight in deciduous forests during the spring and summer months. But what does this little gray and white bird eat? Read on to learn about the diet and foraging behavior of the Red-eyed Vireo.
Insects
Insects make up the majority of the Red-eyed Vireo’s diet. This bird is an actively foraging, foliage-gleaning insectivore, searching leaves, branches, and bark for tasty bugs. Some key insects that the Red-eyed Vireo eats include:
- Caterpillars – The larvae of moths and butterflies are an important food source. Red-eyed Vireos eat caterpillars like gypsy moths, tent caterpillars, and fall webworms.
- Beetles – Beetles of many types are eaten, including weevils, leaf beetles, and long-horned beetles.
- Flies – Flies are a significant part of the Red-eyed Vireo’s diet. They eat craneflies, deer flies, horse flies, and other flying insects.
- Spiders – Although not insects, spiders are arthropods that Red-eyed Vireos readily consume.
- Cicadas
- Treehoppers
- Ants
- Aphids
- Leafhoppers
- Dragonflies
- Grasshoppers
- Crickets
- Midges
- Sawfly larvae
The Red-eyed Vireo uses its sharply pointed beak to pick insects off of leaves and branches. It can also catch flying insects on the wing. This vireo often hangs upside-down to probe for insects on the undersides of leaves.
Fruit and Berries
While insects make up the majority of its diet, the Red-eyed Vireo supplements its diet with fruit and berries, especially during fall migration. Some examples of fruits eaten include:
- Blueberries
- Huckleberries
- Grapes
- Cherries
- Elderberries
- Mulberries
- Raspberries
- Blackberries
- Dogwood berries
- Spicebush berries
- Pokeweed berries
- Virginia creeper berries
The Red-eyed Vireo may play a role in dispersing the seeds of these fruiting plants after eating the fruits.
Nuts and Seeds
In addition to fruit, the Red-eyed Vireo will sometimes eat small nuts and seeds, including:
- Acorns
- American beech nuts
- Maple samaras
- Sumac seeds
- Pine seeds
These foods can provide an important source of fat and protein. The vireo will hammer at seeds with its beak to break them open.
Sap and Tree Cambium
On occasion, the Red-eyed Vireo feeds on sap wells excavated by Yellow-bellied Sapsuckers. It will also peel back bark to eat the nutritious cambium layer of trees. However, these foods make up a very minor part of the vireo’s overall diet.
Foraging Behavior
The Red-eyed Vireo is an active and agile forager, using a variety of techniques to find insect prey:
- Foliage gleaning – This is the most commonly used foraging strategy. The vireo carefully searches leaves and branches for hidden insects.
- Hang-gleaning – It often hangs upside-down to scan the undersides of leaves.
- Hover-gleaning – The vireo will hover briefly to pluck insects off vegetation.
- Berry plucking – Fruit and berries are plucked directly off plants.
- Bark peeling – To access tree cambium, the vireo peels back bark with its sharp beak.
- Aerial flycatching – On occasion, flying insects are pursued and caught in midair.
- Probing – The vireo probes into crevices and holes in search of hidden arthropod prey.
This species often joins mixed-species foraging flocks during migration and in winter. It gleans insects disturbed by other birds in these roving flocks. Pairs may also forage closely together. Overall, the Red-eyed Vireo is a very active and adaptable forager.
Habitat
The Red-eyed Vireo is strongly associated with mature, deciduous forest habitat. It preferentially forages in the following habitats:
- Deciduous forests – especially oak-hickory, maple-beech
- Open woodlands
- Pine-oak barrens
- Old orchards
- Parks and suburban areas with large, scattered trees
Mature trees provide the ideal foraging substrates for foliage-gleaning. The Red-eyed Vireo primarily forages in the mid-canopy zone of forests, searching through leaves in the understory and mid-level branches. It occurs less often in the highest branches and lower shrub layer.
Seasonal Variation
The Red-eyed Vireo’s diet changes somewhat across seasons:
- Spring – Caterpillars and other soft-bodied insects make up a high percentage of the diet during spring breeding season when insect abundance is high and young vireos need protein-rich food.
- Summer – A wider variety of hardy adult insects are eaten, including beetles, ants, flies, leafhoppers, etc.
- Fall – Fruit consumption increases as birds prepare for migration. Berries and fruit supplement insects in the diet.
- Winter – Unknown. It likely eats a variety of insects in South American wintering grounds.
So in spring and summer, insects dominate the diet, while fruit increases in importance as an energy-rich food source before fall migration.
Water
Like most birds, the Red-eyed Vireo needs to drink water regularly. It gets much of its moisture from the foods it eats, but also drinks freely from small pools, puddles, creek edges, rain caught in tree hollows, and other shallow water sources. These songbirds do not wade into deeper water like some species.
Feeding Specialized Young
During the breeding season, adult Red-eyed Vireos feed protein-rich insects to their developing young. Nestlings hatch blind and helpless, entirely dependent on their parents. The female incubates the eggs and broods the altricial young. Both parents feed the nestlings caterpillars, spiders, flies, and other soft-bodied insects, which provide a high-protein diet.
As the nestlings grow, the adults gradually introduce more variety, including beetles, leafhoppers, and other harder-bodied prey. The young leave the nest 9-12 days after hatching, and follow the parents around begging for food for several more weeks, perfecting their insect-foraging skills during this post-fledging period. The young are independent after 4-6 weeks.
Predators and Threats
Young Red-eyed Vireos are vulnerable to predators like snakes, squirrels, chipmunks, raccoons, crows, jays, and cats that may raid nests. Sharp-shinned Hawks and Cooper’s Hawks prey on adults. Parasitic Brown-headed Cowbirds sometimes lay eggs in Red-eyed Vireo nests.
Habitat loss is a long-term threat, as this species depends on mature deciduous forest. Use of pesticides can reduce the insect populations that the vireo depends on. Collisions with towers and windows also cause mortality. However, Red-eyed Vireo populations remain stable overall.
Importance to the Ecosystem
The Red-eyed Vireo fills an important niche as an insect-eating songbird. It consumes vast numbers of caterpillars, beetles, flies, leafhoppers, and other arthropods that could become pests if unchecked. This helps maintain healthy forest ecosystems.
Scientists estimate the Red-eyed Vireo may consume 38% of its body weight in insects daily! With an estimated 84 million Red-eyed Vireos in North America, this represents billions of insect meals during the summer breeding season.
This vireo also contributes to seed dispersal when eating fruits. As a common and widespread songbird, it links disparate habitats together when moving between wintering and breeding grounds. Overall, the Red-eyed Vireo is an integral part of eastern forest food webs.
Summary
The Red-eyed Vireo is primarily an insectivorous songbird that gleans caterpillars, beetles, flies, leafhoppers, and other insects from leaves in forest canopies. It supplements its diet with fruit and berries in fall. The vireo is an agile and adaptable forager, using a variety of gleaning techniques.
Its sharp, pointed beak helps capture elusive prey. Habitat loss and collisions pose threats, but Red-eyed Vireo populations remain secure. This vireo fills an important ecological role consuming billions of insects annually and dispersing seeds. The Red-eyed Vireo’s voracious appetite for insects helps control potential pest species and maintain healthy eastern forests. So the next time you hear its repetitive song in the treetops, you can picture this little gray bird busily gobbling up insects!
