American redstart

Did You Know?

• The American redstart was described by Carl Linnaeus in 1758 under the binomial name Motacilla ruticilla.
• The genus name Setophaga means 'moth eater' from Ancient Greek.
• The specific name ruticilla is Neo-Latin for 'redstart', from Latin rutilus 'red' and the diminutive -cilla.

Description

The American redstart is a smallish warbler with a relatively long tail, making it one of the lightest birds in its family. Weight varies seasonally: males average 8.6 g in summer and 7.2 g in winter, while females drop from 8.7 g to 6.9 g. Standard measurements include a wing chord of 5.5 to 6.9 cm, a tail of 4.9 to 5.8 cm, a bill of 0.7 to 0.9 cm, and a tarsus of 1.5 to 1.9 cm. Breeding males are unmistakable, jet black above with large orange-red patches on wings and tail, and orange breast sides contrasting with white underparts. Other plumages show green upperparts, black central tails, and grey heads. Females and young birds replace the orange with yellow. The orange coloration results from a mix of the red carotenoid canthaxanthin and the yellow carotenoids canary xanthophyll A and B; females possess only the yellow carotenoids. Research indicates age and sex effects on hue, brightness, and saturation, except saturation shows only an age effect. The song consists of musical see notes, and the call is a soft chip.

Distribution and habitat

The American redstart breeds across southern Canada and the eastern United States, wintering in Central America, the West Indies, and northern South America. It is a very rare vagrant to western Europe. During breeding, it inhabits open-canopy, mostly deciduous forests, second growth, and forest edges, feeding in mid to lower tree or shrub levels. On migration, it uses many shrubby areas. On wintering grounds, it occupies nearly all woody habitats but avoids non-forested agricultural areas, often found in shade-grown coffee plantations. Elevations range up to 3000 m in South America but only 1500 m in Jamaica. The species remains stable and abundant, though its numbers are exceeded by the common yellowthroat, yellow warbler, and yellow-rumped warbler due to their wider breeding ranges.

Behavior

American redstarts breed in open woodlands or scrub, often near water, nesting in the lower part of a bush. The female incubates a clutch of 2–5 eggs for 10 to 13 days; young fledge after 9 days and may stay with one parent for up to 3 weeks. First-year males can reproduce but retain female-like plumage, leading to low reproductive success (less than 50%) until year 2, whereas most first-year females breed successfully. A skewed sex ratio produces a surplus of unmated males. The species displays a mixed mating strategy: predominantly monogamous, but about 25% of males are polygynous, maintaining multiple territories. Even in monogamous pairs, up to 40% of offspring are not fathered by the pair male. Male coloration intensity predicts winter territory success, polygyny probability, and paternity proportion. Males are territorial, with superior males occupying moist mangroves and inferior males using dry scrub forests. They feed almost exclusively on insects, caught by flycatching or gleaning from leaves. The tail is often fanned, and birds flash orange or yellow to startle prey. Diet includes caterpillars, moths, flies, leafhoppers, planthoppers, small wasps, beetles, aphids, stoneflies, and spiders, with few berries from barberry, serviceberry, and magnolia.

Mortality

The oldest banded American redstart lived over 10 years, though other adults reach about 5 years. Few survive early life due to vulnerability to terrestrial and aerial predators. Predation peaks during breeding, when eggs and nestlings are abundant. Females brooding often fall prey. Terrestrial predators include red squirrels, fishers, eastern chipmunks, American black bears, flying squirrels, fox snakes, and domestic cats. Aerial predators include jaegers, blue jays, common ravens, northern saw-whet owls, common grackles, northern goshawks, sharp-shinned hawks, and Cooper's hawks.