Warblers are small songbirds that belong to the family Parulidae. There are around 115-130 species of warblers, depending on how they are classified. Warblers are found throughout North America, particularly during their spring and fall migrations. These tiny birds eat a variety of different foods depending on the species, time of year, and local habitat. Their diets consist mainly of insects and spiders during the spring and summer breeding season, shifting to fruits and berries during fall migration and overwintering. Nectar, sap, and seeds round out their diverse diets.
Insectivores During Breeding Season
Most warblers are primarily insectivores, meaning they eat insects and other small invertebrates. They glean insects and spiders from leaves, twigs, branches, and the bark of trees. Some species like the Black-and-white Warbler creep along trunks and branches, probing into crevices of bark to find hidden insects. Others like the American Redstart and Northern Parula sally out from perches to snatch insects like flies and beetles from the air.
Caterpillars make up a substantial part of warbler diets during spring and summer. For nestlings, caterpillars are an excellent source of protein for growth and development. Some common ones eaten include inchworms, gypsy moth caterpillars, tent caterpillars, and fall webworms.
Adult warblers also eat other insects like leafhoppers, true bugs, flying ants, wasps, and bees. They consume a wide variety of beetles such as weevils, leaf beetles, and longhorn beetles. Dragonflies, damselflies, mayflies, caddisflies, stoneflies, and other aquatic insects are snatched by species foraging near water.
Spiders and Other Prey
Spiders are another important prey item for many warblers. Small spiders are snatched from webs and vegetation. Some warblers like the Worm-eating Warbler probe into leaf litter and dead leaves searching for spiders. Others steal spiders from webs, often destroying the web in the process.
Warblers supplement their insectivorous diets with other small invertebrates. Moths, millipedes, centipedes, snails, and worms are all eaten. The Blackpoll and Cerulean Warblers occasionally eat small tree frogs and lizards. A few species like the Connecticut Warbler are known to consume leeches.
Overall the protein-rich insects and spiders consumed by warblers during spring and summer provide energy for breeding and allow adults to continually produce crop milk to feed their nestlings. The abundance of caterpillars is especially important for raising young.
Fruits and Berries During Fall Migration
In fall, as warblers migrate south to their wintering grounds, they shift to eating more fruits and berries. Insects are still part of their diet, but fruits rich in carbohydrates provide excellent energy for their long journeys. Some common fruits eaten by warblers include dogwood, juniper, sumac, Virginia creeper, and more.
Here are some of the berries that different warbler species are known to eat in fall:
Bayberry
Bayberry fruits are waxy blue-gray berries eaten by Yellow-rumped, Magnolia, Cape May, and Blackpoll Warblers. These birds can digest the waxy coating.
Blueberry
Blueberries are softer fruits eaten by many warblers like the Prairie, Black-throated Blue, and Palm Warblers. They provide important carbohydrates.
Cranberry
Cranberries are too big for many warblers to swallow, but some like Palm and Yellow-rumped Warblers can manage them. Their sharp bills can pierce the firm skin.
Grapes
Small native grapes are consumed by a wide variety of warblers including Chestnut-sided, Black-throated Blue, and Orange-crowned Warblers. They offer needed sugars.
Huckleberry
Huckleberries, close relatives of blueberries, are readily eaten by Magnolia, Yellow, and Blackpoll Warblers migrating along the coasts.
Warbler Species | Types of Fruit Eaten |
---|---|
Bay-breasted Warbler | Dogwood, juniper, sumac, blueberry |
Black-throated Blue Warbler | Grapes, blueberry, dogwood, spicebush |
Chestnut-sided Warbler | Grapes, bayberry, cherry, blueberry |
Poison Ivy
Some warblers like the Hooded, Cape May, and Prairie Warbler eat the berries of poison ivy plants. They are apparently immune to the toxic irritants in the plant.
Spicebush
Spicebush fruits are eaten by the Worm-eating, Hooded, Cape May, and other warblers. These red berries provide carotenoids, protein, and fat.
Viburnum
Ripe viburnum fruits are readily eaten by migrants like the Black-throated Blue, Black-and-white, and Blackpoll Warblers. Their high fat content makes them excellent fuel.
Switching to sugary fruits allows warblers to accumulate fat reserves needed for migration. The variety of fruits they eat provides many needed nutrients and energy. Successful foraging during fall is essential for birds to continue their southern journeys.
Nectar, Sap, and Seeds
While not the bulk of their diet, warblers also supplement their insect and fruit eating by consuming nectar, plant sap, and seeds. A few species like the Yellow-breasted Chat and Painted Redstart regularly visit flowers for nectar, acting somewhat like hummingbirds. Sapsucker drillings offer warblers nutritious sap that some occasionally drink.
Small seeds can provide fat and protein. Warblers may eat seeds from plants like thistle, amaranth, knotweed, dock, millet, and various grasses and sedges. Ground foraging species like the Ovenbird, Northern Waterthrush, and Connecticut Warbler probably consume the most seeds. Certain warblers like the Prairie Warbler and Painted Bunting may eat significant amounts of grass and sedge seeds in winter.
These additions to their insectivorous or frugivorous eating habits provide extra nutrition. While less significant overall, nectar, sap, and seeds are still important complementary foods.
Warbler Species | Foods Eaten |
---|---|
Yellow-breasted Chat | Insects, berries, nectar |
American Redstart | Insects, fruit, seeds |
Prothonotary Warbler | Insects, berries |
Foraging Behaviors and Locations
Different warbler species utilize various foraging techniques and behaviors to find their insect and fruit foods. Some of the main ways they search for prey include:
Gleaning
Gleaning insects, spiders, and fruits from leaves, twigs, and bark is the most common foraging strategy. Ovenbirds are consummate gleaners, picking through leaf litter on forest floors.
Hawking
Flycatching warblers like the American Redstart snap passing insects from the air. They sally out to pluck prey and return to a perch.
Hover Gleaning
The Black-throated Green Warbler and Golden-winged Warbler hover briefly next to foliage to grab hidden prey. Their rapid wingbeats allow them to gingerly probe clusters of leaves.
Probing
Warblers like the Orange-crowned search into bark crevices and holes probing with their bills to feel for concealed insects and spiders. The Black-and-white Warbler creeps along trunks probing into grooves.
Skimming
Palm Warblers often forage by skimming low vegetation. They glean insects from the top of grasses, sedges, and other vegetation near wetlands.
Warblers search for food in diverse habitats including:
– Treetops and upper canopy – search for insects and spiders
– Shrubs and understory – pick caterpillars and fruits
– Trunk and branches – probe bark crevices
– Leaf litter – overturned leaves hide insects
– Wetlands – hunt bugs along marshy edges
– Fields – grass seeds supplement diet in winter
Their flexibility in utilizing various microhabitats and food resources allows warblers to flourish across North America.
Differences Between Species
The diverse family Parulidae contains species with some differing foraging behaviors and food preferences:
Ovenbirds
As forest floor specialists, Ovenbirds consume more spiders, beetles, ants, and seeds than arboreal warblers. They also occasionally eat small salamanders.
Waterthrushes
Waterthrushes probe along stream edges eating aquatic insects like mayflies, stoneflies, and caddisflies. They also consume winged ants and beetles.
Yellow-breasted Chat
An oddball warbler, the Yellow-breasted Chat acts somewhat like a flycatcher. It hawks insects from exposed perches and also eats berries and drinks nectar regularly. Chats are more omnivorous than most warblers.
Painted Redstart
Another unorthodox species, the Painted Redstart is highly attracted to army ants. It follows ant swarms to prey on insects and other arthropods flushed by their movement, more so than most warblers.
Yellow-throated Warbler
With a longer, sturdier bill, the Yellow-throated Warbler hammers into bark crevices to pry out insects and spiders, a behavior called bark probing. Other warblers cannot hammer into wood like this species can.
Warbler Species | Unique Foraging |
---|---|
Ovenbird | Consumes many leaf litter insects |
Northern Waterthrush | Probes stream edges |
Golden-winged Warbler | Hover gleans from foliage |
These variations in foraging behavior and prey selection allow different warbler species to divide resources and coexist by reducing competition. Their diverse feeding habits complement each other.
Conclusion
Warblers consume a varied diet primarily consisting of insects like caterpillars, spiders, fruits, and berries. Different species utilize diverse foraging techniques and behaviors to find food. Their dietary flexibility allows warblers to nest successfully across North America and undertake long annual migrations. By switching from eating insects to fruits seasonally, warblers can breed and raise young efficiently then fuel their long journeys to the tropics. The variety of foods eaten provides complete nutrition to sustain warbler populations. Their diverse foraging strategies and food types are key adaptations allowing warblers to flourish.