The American Redstart is a small songbird that is found throughout much of North America. Redstarts are insectivores, meaning they eat mostly insects. Their diet consists of a variety of small invertebrates including caterpillars, flies, beetles, spiders, and grasshoppers. Redstarts forage for insects while flitting through trees and shrubs. With their sleek bodies and pointed bills, they are well-adapted for picking insects off of leaves and branches. Read on to learn more about the diet and foraging habits of the American Redstart.
Typical Foods Eaten
The American Redstart’s diet is composed primarily of insects and other small invertebrates. Some of their favorite foods include:
- Caterpillars – Caterpillars make up a substantial part of the Redstart’s diet. They feast on a variety of caterpillar species including gypsy moths, spruce budworms, tent caterpillars, and more.
- Beetles – Beetles are another important source of food. Redstarts will eat beetles from many different families such as long-horned beetles, leaf beetles, and weevils.
- Flies – Flies are a key prey item for Redstarts during the summer months. They capture many types of flies including crane flies, horse flies, deer flies, and robber flies.
- Spiders – Redstarts glean small spiders off of vegetation. Orb-weaver spiders and crab spiders are among the types eaten.
- Grasshoppers – Grasshoppers are taken when available. Redstarts are agile hunters, able to grab even fast moving grasshoppers.
- Moths – Moths are also taken, often during evening hours when moths are active.
- Ants – At times Redstarts will supplement their diet with ants, especially tree-dwelling species like carpenter ants.
- Aphids – When aphid populations boom, Redstarts will gorge on these plant-sucking insects.
- Leafhoppers – Tiny insects like leafhoppers and treehoppers are preyed upon when other food sources are scarce.
These are the main components of the American Redstart’s insectivorous diet. They generally avoid eating seeds or fruit. By feeding on insects, Redstarts help control pest populations that can damage vegetation. Their choice of small invertebrates provides them with adequate nutrition and energy to sustain their active lifestyle.
Foraging Behavior
Redstarts have a very characteristic foraging style. They actively flutter and flit about through trees and shrubs in search of insect prey. They move quickly, fanning their colorful tails open and snapping them shut as they chase down insects. Redstarts often begin foraging low in a tree and work their way up into the canopy as they glean insects off of leaves, branches and trunks. They also readily hawk insects in mid-air, darting out from perches to grab flies and moths. Here are some more details on how Redstarts find and capture their prey:
- Glean insects from foliage – Their most common foraging technique is picking stationary or slow-moving insects off of leaves and branches as they move through the trees.
- Probe into crevices – They use their slender beaks to probe into crevices and under bark to find hiding insects.
- Hang upside down – Redstarts will hang upside down or sideways along branches to scout for food beneath them.
- Catch insects on the wing – Launching into swift mid-air flights to catch insects in flight. Especially useful for nabbing flying insects like flies and moths.
- Snatch prey from spiderwebs – They often snatch spiders and insects caught in webs to eat.
- Pump tail as visual flush signal – Their pumping tail is thought to startle insects into movement, revealing their location to the bird.
Redstarts forage actively throughout the day, with peaks often in the early morning and in the evening around dusk when certain insects are more active. They aggressively defend feeding territories from competitors during nesting season but may join loose foraging flocks after breeding season. Their energetic routine keeps them stocked up on nutritious insects to power their metabolism.
Adaptations for Eating Insects
American Redstarts have many physical and behavioral adaptations that allow them to thrive on an insectivorous diet:
- Pointed bill – Their bills are perfect for picking insects off vegetation, probing into crevices, and catching insects in mid-air.
- Wide gape – They can open their mouths very wide to snatch larger prey.
- Swift flight – Their flight abilities allow them to expertly chase insects on the wing.
- Maneuverable shape – Long tail and wings give them agility to dart through branches and grab prey.
- Enhanced color vision – See UV light reflected off of flowers used by foraging insects.
- Special digestive system – Short intestine and large gizzard to process insect exoskeletons.
- Fast metabolism – High metabolism powers their active foraging strategy.
Interestingly, the bright coloring of male Redstarts, with their black, orange and white plumage, also seems to play a role in their hunting strategy. Research indicates the conspicuous flashing of the colorful tail frightens insects into revealing their position. The combination of physical features, visual senses and energetic behavior equip Redstarts exceptionally well for seeking insect prey among trees and shrubs.
Amount of Food Consumed
Redstarts are voracious predators that consume a large quantity of insects each day. One study that examined stomach contents of collected specimens found that the average mass of food in a Redstart’s stomach was around 0.4-0.5 grams. However, their stomach empties quickly into the intestines so this likely represents just a snippet of what they eat during a full day of foraging.
Given their high activity level, it has been estimated that Redstarts may eat 80% or more of their body weight in insects every day during summer. The typical body mass of Redstarts ranges from 6-9 grams. So an 8 gram Redstart might eat around 6-7 grams of insects daily. With a diet composed primarily of small invertebrates like flies, beetles and spiders, that translates to devouring several hundred individual insects each day!
Their drive for eating huge quantities stems from the high demands of migration and breeding. Insects provide the perfect food for fueling their intensive lifestyle. By consuming such a large volume of insects, Redstarts also fill an important ecological role in regulating populations of harmful pest species.
Provisioning Young
Redstarts are devoted parents that work tirelessly to provide food for their chicks. The female builds the nest and incubates the eggs, but both parents share duties of caring for the hatchlings. Nestlings are completely dependent on their parents to supply meals. The adults make frequent trips to the nest with beakfuls of insects to feed the hungry young.
Nestling Redstarts require huge amounts of protein-rich food to sustain their rapid growth and development. Researchers have found that adults make between 5-17 feeding visits per hour to provide for nestlings. The amount of food brought increases dramatically as the chicks grow. For the first 5 days after hatching, each nestling is fed about 0.3 grams per hour. By days 9-11 that intake is up to 4 grams per hour!
Some of the insects commonly provisioned to nestlings include caterpillars, grasshoppers, beetles, crickets, ants and spiders. The adults often prioritize larger prey items when feeding young. Both parents work tirelessly from dawn to dusk, totaling hundreds of feeding trips daily to satisfy the appetite of their fast-growing brood.
Changes in Diet Over the Year
The diet of American Redstarts varies somewhat across seasons due to fluctuations in food availability as well as changing nutritional needs. Here are some of the shifts that occur:
- Spring migration – Seek calorie-dense foods to fuel migration including bees, beetles and ants.
- Breeding season – Favor caterpillars and other soft-bodied prey to provision young.
- Molting season – Target calcium and protein-rich insects to aid feather regrowth.
- Fall migration – Pack on fat by eating berry pulp and switching to more ants and wasps.
- Winter – Expand diet breadth to include plant material and seeds when insects are scarce.
The key driver of dietary changes across the annual cycle is the availability of different insects and other food resources. But Redstarts also exhibit flexibility to shift their diet to take advantage of certain prey when their nutritional demands change. This adaptability helps sustain them throughout the year.
Geographic Differences
Populations of Redstarts across North America utilize slightly different prey resources depending on the local habitat. Here are some geographic differences in diet:
- Eastern forests – Eat many moth and butterfly caterpillars that feed on deciduous trees.
- Boreal forests – Consume more spruce budworm caterpillars and spiders.
- Western mountains – Forage on pine caterpillars like pine beauty moths.
- Southwestern canyons – Prey on colorful ants, beetles and caterpillars.
- Mangrove forests – Feed on crabs and flies associated with coastal estuaries.
- Mexican highlands – Favor grasshoppers and other insects of high elevation meadows.
Regardless of location though, Redstarts fill the niche of a foliage-gleaning insectivore, feeding on a wide array of small invertebrates. They exhibit versatility in taking advantage of whatever prey is abundant in their particular habitat.
Hunting Strategies
Redstarts are intelligent hunters that utilize a variety of strategies and techniques to maximize their insect-foraging success. Some of their hunting strategies include:
Perch-hunting
Perch on a bare branch and swoop out to snatch passing insects.
Hover-gleaning
Hover briefly next to foliage to pluck insects off leaves and branches.
Fanning tail
Use tail as a flashing “flush signal” to startle concealed insects into moving.
Probing bark
Probe slender bill into cracks in bark to find hiding insects.
Hang-gleaning
Hang upside-down to scan for insects under branches and leaves.
Flycatching
Dart out aerially from perch to catch insects on the wing.
Their hunting success depends on using multiple techniques appropriate for the situation. This versatility and behavioral plasticity allows Redstarts to flourish across many habitat types.
Impact of Pesticides
American Redstarts face threats from pesticides in both their breeding and wintering habitats. Broad use of insecticides aimed at controlling crop pests or stinging insects can inadvertently impact Redstarts by reducing insect prey populations. Some types of insecticides are also directly toxic if consumed by birds.
Studies have revealed insectivorous bird species to be more susceptible to poisoning from pesticide accumulation. Agriculture-dominated landscapes where pesticides are heavily used show lower densities of Redstarts. Neonicotinoid insecticides are of particular concern for harming birds dependent on insects. Maintaining habitat heterogeneity with patches of pesticide-free native vegetation can provide refuge areas. More judicious use of pest control methods is needed to minimize harm to Redstarts and other insect-eating species.
Conclusion
American Redstarts are fascinating birds that are strongly tied to their insect prey. They are equipped with superb adaptations for hunting and consuming the many types of invertebrates that form their diet. Redstarts exhibit flexibility across seasons and regions in targeting whatever insects are most abundant. Their large consumption of insects provides an important ecosystem service. Conserving the health of Redstart populations requires protecting them from excessive pesticide exposure and preserving habitat heterogenetiy across forest landscapes. Redstarts serve as an indicator of ecosystem vitality through their reliance on thriving insect populations to sustain their energetic lifestyle centered on insects.