Chaetura pelagica (Linnaeus, 1758)

Species Introduction

This description covers the species Chaetura pelagica, commonly known as the chimney swift, a medium-sized swift.

Size Measurements

It measures 12 to 15 cm (4.7 to 5.9 in) in length, with a 27 to 30 cm (11 to 12 in) wingspan, and weighs 17 to 30 g (0.60 to 1.06 oz).

Sexual Dimorphism

Males and females have identical plumage, though males on average are slightly heavier than females.

Adult Plumage

Adult plumage is dark sooty olive on the upperparts and grayish brown on the underparts, with a slightly paler rump and uppertail covert feathers, and a noticeably paler throat.

Upperpart Coloration Distinction

Among all Chaetura swifts, this species has the most uniformly colored upperparts, with very little contrast between the back and rump.

Soft Part Coloration

Its beak, feet, and legs are all black, and its iris is dark brown.

Juvenile Plumage

Juvenile plumage, which young birds keep for their first few months after fledging, is very similar to adult plumage, differing only by having whitish tips on the outer webs of the secondaries and tertials.

Wing Structure

The chimney swift has long, slender, curved wings that extend up to 1.5 in (3.8 cm) past the bird's tail when folded.

Wing Aerodynamics

Its pointed wingtips reduce air turbulence and thus drag during flight.

Wing Bone Structure

The humerus (the inner wing bone) is quite short, while the more distal bones further along the wing are elongated; this combination lets the bird flap very quickly.

Flight Movement

In flight, the chimney swift holds its wings stiffly, alternating between rapid, quivering flaps and longer glides.

Flight Shape Description

Its flight shape is widely described as "a cigar with wings," a description first coined by Roger Tory Peterson.

Wing Beat Synchrony

While the bird often looks like it beats its wings asynchronously during flight, photographic and stroboscopic studies have confirmed it beats them in unison.

Asynchronous Wing Beat Illusion

The illusion of asynchronous beating comes from its very fast, highly erratic flight that includes many rapid direction changes.

Leg Characteristics

Like all swifts, the chimney swift has very short legs.

Foot Structure

Its feet are small but strong, with very short toes tipped with sharp, curved claws.

Toe Adaptation

Its toes are anisodactyl (three facing forward, one facing back) like most birds, but the chimney swift can swivel its back toe (the hallux) forward to get a better grip.

Leg Skin Structure

Unlike the legs and feet of most birds, the chimney swift's legs and feet have no scales and are instead covered in smooth skin.

Tail Size

Its tail is short and square, measuring only 4.8 to 5.5 cm (1.90 to 2.15 in) in length.

Tail Adaptations

All ten of its tail feathers have shafts that extend up to 1.3 cm (0.5 in) beyond the feather vanes, ending in sharp, stiff points that help the bird prop itself against vertical surfaces.

Eye Bristles

The chimney swift has large, deep-set eyes, each protected by a small patch of coarse, black, bristly feathers in front of the eye.

Bristle Function

The swift can adjust the angle of these feathers, which may help reduce glare.

Visual Acuity Adaptations

It is far-sighted, and like some birds of prey, it is bifoveal: each eye has both a temporal and a central fovea.

Fovea Function

These small retinal depressions are where visual acuity is highest, and they make the chimney swift's vision especially sharp.

Focus Ability

Like most vertebrates, it can focus both eyes at the same time, but it can also focus a single eye independently.

Bill Size

Its bill is very small, with a culmen that measures only 5 mm (0.20 in) long.

Gape Adaptation

However, its gape is very large, extending back below its eyes and allowing the bird to open its mouth very widely.

Beak Structure Difference

Unlike many insectivorous birds, it lacks rictal bristles at the base of the beak.

Breeding Range

The chimney swift is a widespread breeding visitor to most of the eastern half of the United States and the southern portions of eastern Canada.

Migration Pattern

It migrates to South America to spend the winter.

Vagrant Records

It is a rare summer visitor to the western United States, and has been recorded as a vagrant in Anguilla, Barbados, Greenland, Jamaica, Portugal, the United Kingdom, and the U.S. Virgin Islands.

Habitat

It can be found over open country, savanna, wooded slopes, and humid forests.

Wintering Ground Discovery

The chimney swift's wintering grounds were not discovered until 1944, when bands from North American banded (ringed) birds were recovered in Peru.

Band Recovery Context

An indigenous Peruvian person had been wearing the bands as a necklace.