Quick Answers
The Vaux’s swift and chimney swift are two very similar bird species found in North America. The main differences between them are:
- Range – Vaux’s swifts are found along the western coast of North America, while chimney swifts are found in central and eastern North America.
- Size – Vaux’s swifts are slightly larger than chimney swifts.
- Color – Vaux’s swifts are a more uniform dark color, while chimney swifts have a contrasting pale throat.
- Habitat – Vaux’s swifts nest in hollow trees, chimney swifts nest in chimneys and other man-made structures.
- Taxonomy – Vaux’s swifts and chimney swifts are in different genus groups within the swift family.
Vaux’s swifts (Chaetura vauxi) and chimney swifts (Chaetura pelagica) are two similar bird species found in North America. Both are in the swift family Apodidae, known for their speedy flight and ability to spent most of their lives airborne. Swifts as a group are aerial insectivores, catching insects on the wing.
Vaux’s swifts and chimney swifts overlap in range during migration and wintering, but they breed in distinct areas of North America. Vaux’s swifts nest along the western coast from Alaska south to California, while chimney swifts are found widely in the central and eastern parts of the continent.
Though they were once considered the same species, Vaux’s and chimney swifts are now classified as different genus groups based on physical, behavioral, and genetic differences. However, as aerial foragers that utilize man-made structures for nesting, their lifestyles and adaptations are very comparable.
Range and Distribution
The ranges of Vaux’s and chimney swifts differ, which is a key distinction between these two species. Vaux’s swifts breed along the western coast of North America, from southeastern Alaska south through western Canada to northern California. They migrate through the western interior of the continent to wintering grounds in central Mexico and even as far as northwestern South America.
In contrast, chimney swifts breed primarily in central and eastern parts of North America. Their breeding range extends from Nova Scotia west to the Rocky Mountains and south to Florida and Texas. Chimney swifts migrate through the eastern half of the continent to winter in northwestern South America.
During migration periods, Vaux’s swifts and chimney swifts overlap considerably along the Mississippi River valley. Both species also overlap to some degree in their wintering grounds in South America, though Vaux’s swifts tend to winter mostly on the Pacific side while chimney swifts are concentrated on the Atlantic side.
Vaux’s Swift Breeding Range
The core breeding range of the Vaux’s swift includes:
- Western British Columbia in Canada
- Western Washington, Oregon, and California in the United States
- Small parts of western Montana, Idaho, and northern Nevada
Chimney Swift Breeding Range
The breeding range of the chimney swift includes:
- Southern Canada from British Columbia to Nova Scotia
- Most of the eastern and central United States, from the Atlantic coast to the Rocky Mountains
- Ranging as far south as Florida and Texas
Physical Differences
Though Vaux’s and chimney swifts appear very similar on the wing, there are some subtle physical differences between these two species. These include size, proportions, and coloration.
Size
Vaux’s swifts are slightly larger than chimney swifts, with the following average measurements:
| Species | Length (inches) | Wingspan (inches) |
|---|---|---|
| Vaux’s Swift | 5.1 – 5.5 | 12.2 |
| Chimney Swift | 4.7 – 5.1 | 11.8 |
As these averages show, Vaux’s swifts are about half an inch longer than chimney swifts. They also have a slightly broader wingspan on average.
Proportions
Vaux’s swifts have proportionally longer wings and tails than chimney swifts. Their wings are also more pointed. These adaptations suit the Vaux’s swift’s lifestyle of nesting and roosting in tall hollow trees. The chimney swift has proportionally shorter, more rounded wings for maneuvering in confined spaces like chimneys.
Color
Both swifts are dark colored birds, but the Vaux’s swift has a more uniform sooty gray-brown appearance compared to the chimney swift. Chimney swifts have a slightly paler gray throat and belly, creating more contrast in their coloration.
Behavioral Differences
Beyond physical differences, Vaux’s and chimney swifts show some subtle variations in their behavior tied to their separate nesting habitats.
Nest Sites
One of the main behavioral differences between these species is nest site selection. Vaux’s swifts nest exclusively in large hollow trees, especially tall, aging evergreens. In contrast, as their name implies, chimney swifts nest mainly in chimneys, as well as other man-made structures like air vents and wells.
Roosting
When not nesting, swifts roost communally in large groups. Vaux’s swifts generally prefer roosting in hollow trees, though some may use man-made structures. Chimney swifts are more flexible in roost site selection but strongly prefer urban environments. Both species migrate and roost together in mixed groups in certain areas.
Foraging
Vaux’s and chimney swifts forage aerially in continuous flight, catching insects on the wing. Their foraging behaviors appear almost identical. However, chimney swifts may be better adapted to foraging around human structures in urban areas.
Vocalizations
Both swifts utilize very high-pitched vocalizations for communicating while in flight. However, their vocalizations differ and researchers can distinguish between the species audibly. This may help the birds identify their own species within mixed migrating and wintering flocks.
Taxonomy and Genetics
Vaux’s swifts and chimney swifts were considered the same species until the late 19th century. Based on differences in morphology, behavior, and geographic range, ornithologists determined they warranted separation into two different species groups. Today, these differences are reinforced by genetic evidence.
Genus
Vaux’s swifts are placed in the genus Chaetura. The chimney swift is placed in Chaetura as well but in its own subgenus Chaetura (Chaetura) based on physical and genetic markers. So while they are still closely related, chimney swifts sit in their own evolutionary branch within the broader Chaetura genus.
Genetic analysis
Recent genetic studies have looked at the degree of molecular divergence between Vaux’s and chimney swifts. Analyses of mitochondrial DNA sequences have estimated the two species diverged from each other approximately 2 million years ago. This supports the classification of the birds as separate swift species within their own subgenera.
Similarity in Threats and Declines
Despite the differences between Vaux’s and chimney swifts, both species face similar conservation threats today. Due to habitat loss and other factors, both swifts have declined significantly in numbers in recent decades.
Major threats contributing to reductions in swift populations include:
- Loss of nesting and roosting sites
- Reduced availability of aerial insect prey
- Climate change disrupting migration and breeding
- Pesticide use reducing insect food sources
Vaux’s swifts rely on the availability of large, old hollow trees for nesting. Due to logging and development, loss of these crucial nest sites has contributed to population declines. Similarly, chimney swifts have lost nesting habitat as fewer suitable chimneys are available in modern buildings.
Though still numerous, both Vaux’s and chimney swift populations have declined by around 2.5% per year in recent decades. Ongoing conservation efforts for both species focus on preserving and providing artificial nesting sites, reducing pesticide use, and keeping critical habitat intact across their ranges.
Conclusion
Vaux’s swifts and chimney swifts exhibit key differences that distinguish them as separate swift species endemic to North America. Vaux’s swifts are larger and slimmer, with more uniformly dark plumage. They nest exclusively in hollow trees along the western coastal regions. Chimney swifts are smaller with paler throats, adapted for maneuvering in confined spaces where they nest in chimneys and other structures in central and eastern parts of the continent.
Despite being in different genus groups, Vaux’s swifts and chimney swifts still share common traits and challenges as aerial insectivores dependent on specific nesting habitats. Ongoing conservation efforts for both these unique North American swifts are aimed at better understanding and protecting the ecosystems that sustain their populations across the continent.
