The scarlet tanager ( Piranga olivacea ) is a striking medium-sized songbird, a Neotropical migrant that breeds across eastern North America and winters in northwestern South America. The species is known for its vibrant plumage and preference for mature deciduous forests. This article delves into the intricate details of the scarlet tanager's diet and foraging behavior, exploring its adaptations, seasonal variations, and ecological significance.
Identification and Habitat
Male scarlet tanagers in breeding plumage are easily recognizable with their bright red bodies and contrasting black wings and tail. Females, immature birds, and males during the non-breeding season exhibit a duller appearance, with olive-green upperparts and yellowish underparts. While females have greenish-gray wings, males retain their black wings throughout the year. Their song is often described as similar to a robin with a sore throat, accompanied by a distinct “chip-burrr” call note.
Scarlet tanagers inhabit a variety of forest types, but they are primarily found in large tracts of mature deciduous or mixed forests, particularly those dominated by oaks, maples, and beeches. These area-sensitive birds require extensive forest cover for nesting. However, after breeding, they may venture into early successional habitats to take advantage of increased foraging opportunities.
General Foraging Behavior
Scarlet tanagers are primarily insectivorous, foraging mostly in the tall trees, especially oaks, seeking insects among the foliage. They move deliberately through the canopy, often hovering momentarily while capturing prey from leaves, bark, and flowers. They also exhibit flycatching behavior, darting out to catch insects in mid-air before returning to their perch, a hunting style known as "sallying". In colder weather, they may forage in low shrubs or on the ground.
Diet Composition
Insects
During the summer breeding season, insects constitute the major portion of the scarlet tanager's diet. They consume a wide variety of insects, including:
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- Caterpillars
- Moths
- Beetles
- Wasps
- Bees
- Aphids
- Cicadas
- Leafhoppers
- Spittlebugs
- Treehoppers
- Plant lice
- Scale insects
- Termites
- Grasshoppers
- Locusts
- Dragonflies
- Dobsonflies
- Ants
- Sawflies
They also consume spiders, snails, worms, and millipedes. They have been observed to rub stinging insects, such as bees and wasps, against a branch to remove the stinger before consumption. Small prey items are swallowed whole, while larger prey is killed by beating it against a branch.
Fruits and Berries
In addition to insects, scarlet tanagers also consume wild fruits and berries, especially during migration and in the fall and winter when insects become less available. They are known to eat a variety of berries, including:
- Mulberry
- Elder
- Sumac
- Blackberries
- Raspberries
- Huckleberries
- Juneberries
- Serviceberries
- Strawberries
- Chokeberries
Berries provide essential nutrients like sugars, fats, vitamins, and antioxidants, which are particularly important for maintaining energy during migration and periods of food scarcity.
Foraging Strategies
Scarlet tanagers exhibit a variety of foraging strategies depending on the type of prey and the environment. Some of these strategies include:
- Gleaning: Walking along branches high in the canopy or vertically on tree trunks to probe the bark for insects.
- Hovering: Hovering with fast wingbeats to grab insects from leaves, bark, and flowers.
- Flycatching (Sallying): Catching flying insects in mid-air.
- Ground Foraging: Capturing prey on the forest floor, especially in cold weather.
Seasonal Variation in Diet
The diet of the scarlet tanager varies seasonally, reflecting the availability of different food sources. During the summer breeding season, insects are the primary food source, providing the necessary protein for growth and reproduction. As the breeding season ends and fall approaches, the diet shifts to include more fruits and berries. This shift helps the birds build up energy reserves for migration. The winter diet of scarlet tanagers is not well known.
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Impact of Habitat Fragmentation
Scarlet tanagers are sensitive to habitat fragmentation, which can negatively impact their foraging success and overall survival. Habitat fragmentation occurs when large, continuous forests are broken up into smaller, isolated patches, often due to human activities. This fragmentation can lead to:
- Reduced foraging opportunities: Smaller forest patches may not provide sufficient food resources to support scarlet tanager populations.
- Increased nest predation and brood parasitism: Fragmented habitats are more accessible to predators and brood parasites like cowbirds, which can reduce reproductive success.
- Population declines: As a result of reduced foraging success and increased predation and parasitism, scarlet tanager populations may decline in fragmented habitats.
Conservation Strategies
To protect scarlet tanager populations, conservation efforts should focus on:
- Protecting and maintaining large, contiguous tracts of mature deciduous and mixed forests: This will ensure that breeding populations have sufficient territory and foraging resources.
- Managing young forests with a mix of fruiting trees and shrubs: This can enhance post-breeding foraging areas.
- Minimizing forest fragmentation: Conservation easements and land acquisitions can help prevent further habitat fragmentation.
- Promoting responsible pet ownership: Keeping cats indoors can reduce predation on birds.
- Reducing bird collisions with buildings: Making glass more visible to birds can minimize collision mortalities.
Vocalizations and Territoriality
Scarlet tanagers are known to be monogamous and highly territorial. Males arrive at their summer breeding grounds before females and establish territories through singing. These "singing wars" involve males singing from exposed perches to defend their territories from neighboring males. To maintain his territory, male scarlet tanagers use a combination of singing, displaying aggressive behaviors like chasing, and physically confronting other males. Both male and female scarlet tanagers sing during the breeding season, although the female's song is a shorter and softer version of the male's. She typically sings in answer to the male’s song and while she is gathering nesting material.
Nesting and Reproduction
Scarlet tanagers typically nest in a large, unbroken, wooded tract and high in a deciduous tree-often, but not always-an oak. The nest is situated well out from the trunk on a horizontal limb. The nest is a shallow open cup made of twigs, rootlets, and weed stems and lined with fine grasses or pine needles. Females lay 3-5 eggs, which they incubate for about two weeks. Both parents participate in feeding nestlings that fledge after approximately 9-15 days. After breeding, adult males molt their vibrant red and develop female-like olive green plumage. However, keen-eyed birders can still spot the difference between the two sexes: males retain their black wings and tail feathers.
Read also: Tanager's Feeding Habits