Black swifts (Cypseloides niger) are fascinating migratory birds found throughout western North America. As their name suggests, these swift-flying birds are entirely coal black with long, curved wings designed for speed and agility in flight. Unlike many other bird species, black swifts spend an incredible amount of time flying, only coming to land for breeding purposes. But when winter approaches, do these aerial acrobats migrate and if so, where do they go?
Overview of black swifts
Here are some quick facts about black swifts:
– Species: Cypseloides niger
– Average length: 18-22 cm
– Average weight: 55 grams
– Diet: Flying insects like flies, beetles, ants, mosquitoes, more
– Breeding habitat: Rocky cliffs near waterfalls and sea coasts
– Nonbreeding range: Western North America from Alaska to Central America
– Migration: Suspected to migrate but exact routes unknown
As their scientific name suggests, black swifts are closely related to other swifts and swalllows belonging to the families Apodidae and Hirundinidae. There are four species of swifts that occur in North America including the chimney swift, Vaux’s swift, and white-throated swift.
Breeding and nesting habits
During spring and summer breeding months, black swifts are most frequently found along coastal areas or near waterfalls and steep, inaccessible cliffsides. Their nests consist of mats of algae, moss, and pine needles glued together with saliva and attached to vertical rock surfaces protected by overhangs.
Female black swifts lay 1-4 eggs which are incubated for 18-25 days until hatching. Nestlings fledge in another 6-7 weeks and remain dependent on their parents for an additional 2-3 weeks while they learn to hunt flying insects and refine their aerial skills.
Do black swifts migrate?
Unlike many of their relatives, black swifts are uniquely adapted to be in continuous flight throughout the year. As a result, determining their migratory movements has been challenging for ornithologists. Here’s an overview of what we know so far:
Limited banding data
Banding data provides some of the best insights into migratory connectivity but there have been relatively few black swifts banded to date. Those that have been tracked seem to migrate south to Mexico and Central America after breeding. However, more data is needed to confirm migration routes.
Anecdotal winter sightings
There have been sporadic winter sightings of black swifts along the Pacific Coast and American Southwest which suggests that some individuals may remain resident year-round. However, the size and origins of any non-migratory population are unclear.
Reduced winter range
Most records indicate a substantial reduction in the winter range of black swifts suggesting a likely migratory movement out of more northern breeding territories even if their ultimate destination is unknown. Their winter range concentrates along the southern Pacific coast into Central America.
| Season | Range |
|---|---|
| Breeding (May-Aug) | Western North America from Alaska to Southern California |
| Nonbreeding (Sep-Apr) | Along Pacific Coast from Northern California to Central America |
Lack of winter nesting records
If black swifts were resident year-round, we would expect winter nesting records from across their breeding range in the US and Canada. However, all nesting data comes from spring and summer months which indicates birds vacate breeding sites in winter.
Changes in flock sizes
Breeding black swifts gather in small flocks near cliffside habitats. In migration and winter, black swifts assemble in much larger flocks sometimes numbering in the thousands. This flocking behavior may facilitate migratory movements.
Migration theories
Without direct tracking data, the migration habits of black swifts remain speculative. Here are two leading theories:
Nomadic migration
Black swifts may not follow strict migratory pathways and fixed wintering sites. Instead, they may disperse more nomadically in search of adequate flying insect prey as cold temperatures force them to move south. This would explain the lack of well-defined migratory routes between breeding and wintering grounds.
Transoceanic migration
Some experts speculate that black swifts may undergo a transoceanic migration to South America similar to many shorebirds. This would allow them to take advantage of plentiful rainforest flying insects. However, actually documenting transoceanic crossings has not yet been achieved.
Future research directions
Expanding black swift banding studies and deploying new tracking technologies could provide more conclusive data on migratory movements. Here are some promising research approaches:
Geolocators and satellite tags
Light-level geolocators and GPS satellite transmitters can map detailed migratory routes over multiple seasons. But given black swifts’ small size, tags must continue to shrink for improved deployment.
Night flight call monitoring
Recording and triangulating night flight calls during migration could reveal more about migratory stopovers, directions, and endpoints. This has been useful in studying other avian migrants.
Stable isotope analysis
Analyzing stable hydrogen isotopes in feathers and claws can help determine the geographic origin of birds during molting periods. This could reveal origins of wintering birds.
Citizen science reporting
Expanding citizen science data collection through online reporting tools like eBird may improve documentation of winter occurrences and their associated flock sizes.
Conclusion
In summary, the migration patterns of black swifts remain one of the great unsolved mysteries of North American avian biology. While circumstantial evidence points to likely seasonal movements out of northern and high elevation breeding sites, more research is needed to conclusively determine migratory routes, end points, and behaviors. Solving the mystery of black swift migration will require an array of high-tech tracking tools along with rigorous analysis of historical and citizen science records. Unlocking the migration secrets of these aerial masters will be an exciting achievement for future ornithologists. While we don’t yet have all the answers about black swift migratory habits, the journey to solving this mystery promises to reveal fascinating new details about the biology of swifts and their incredible adaptations for life in flight.
