Black Swifts are primarily a mountainous species in its continental range (Chantler and Driessens 1995) and are difficult to discern from other swifts in flight. The species forages far and wide from its breeding site and its flight patterns include sudden turns, steep downward plunges and hurried upward flights. There is no documentation of this species resting or perching except at nest sites. It nests at waterfalls on cold, damp, dark ledges. The species arrives late to the breeding grounds (Hirschman et al. 2007) after traveling >7,000 km back up from its wintering areas in South America (Beason et al. 2012), returning with great fidelity to its colony and even to its own nest (Collins and Foerster 1995). Once its single chick has reached the ability to self-regulate its body temperature, the adults may forage all day long leaving the young to be fed only intermittently all night long (Collins 1998). The species has a very prolonged breeding period and young have been documented to fledge as late as mid-October (Hirschman et al. 2007).
Black Swift does not appear to exhibit territorial behavior in nesting, roosting or foraging activities and defensive behavior has not been documented. This species demonstrates strong fidelity to the colony site and even to particular nests (Collins and Foerster 1995; Lowther and Collins 2002; Levad et al. 2008). Nests may be closely spaced as at Fulton Resurgence Cave in Colorado, where 12 nests are located within 21 linear m (K. M. Potter personal observation). After over 12 years of almost daily observations of Black Swifts in Colorado, three swifts roosting at a nest, especially at night, have been observed (S.E. Hirshman personal communication). During a camera surveillance study of Black Swift nesting behavior, Gunn (2010) photo-documented five occasions when three adult birds were in the vicinity of the nest, either on the nest, perching at the edge of it, perching on rocks very near it, or flying into or away from it. Four of these occasions were at night. Levad et al. (2008) suggests that nest placement within a colony appears to be driven by the availability of niches or shelves for the nests within suitable nesting habitat rather than by territorial behaviors, as nesting habitat may be the limiting factor for Black Swift populations. Because of their unique nest site preferences, Black Swifts have few known competitors for nest sites (Wiggins 2004).
The species appears not to defend foraging habitat as it is widely documented to forage regularly in large flocks of thousands in British Columbia in both breeding season and migration (Udvardy 1954) and with other swifts and swallows (Joblin 1955; Lowther and Collins 2002). During fall migration about 15 Black Swifts were found with ca 150 White-collared Swifts (Streptoprocne zonaris) gathered in a compact group, roosting each night for about a week in Cañón de Julumito on the Rio Cauca ca 6 km southwest of Popayan, Columbia, in Central America (Stiles and Negret 1994).
No information on territorial behavior on their winter grounds.
Nothing is known about sexual behavior on the wintering grounds. Copulation at the nest was not documented by Gunn (2010) during an entire breeding season of photos collected by a motion-activated camera. Copulation has not been documented by Hirshman (Hirshman et al. 2007, S.E. Hirshman pers. comm.) over an observation period of 11 years. Foerster (1987) observed two swifts flying in unison in early June that locked bodies, copulated and tumbled downward for 3-4 seconds before breaking off. Behaviors associated with pair formation and maintenance include pair chase and group chase which involves swifts engaging in high-speed dives and erratic maneuvers during middle and early breeding season (Marín 1997). The species is thought to be monogamous (Lowther and Collins 2002).
Social and interspecific behavior
Discussion in Territoriality suggested the species does not engage in interspecific aggression while foraging for food; this may be due to the species evolved aerodynamic ability to forage at greater distances and at greater heights. Collins (1998) noted the species has an expanded capacity to carry more insects than competing species. There is no evidence of interspecific aggression with other nesting species near Black Swift colonies. The very specialized nature of Black Swift nest locations may preclude direct competition with other species for nesting niches. A single pair of Cordilleran Flycatcher (Empidonax occidentalis), Townsend’s Solitaire (Myadestes townsendi), and of American Dipper (Cinclus mexicanus) often is found in close proximity to many Black Swift colonies but these species have already begun nesting when most swifts are just returning to their colonies (K.M. Potter personal observations).
Adult Black Swifts have few natural enemies due to their extreme flight speeds and aerial habits. The few instances of documented predation available name Peregrine Falcon (Hunter and Hazard 1998) and Merlin (Swarth 1924a; Laing 1938) as aerial predators. The strategic placement of nests at waterfalls and other wet locations by Black Swifts prevents ground access from typical terrestrial predation. The placement of nests in rock niches provides overhead cover and when combined with the dark skin and downy feathers of the camouflaged chicks typically provides protection from aerial predation, but Black Swift egg shells and corvid feathers were found on two consecutive years where a nest was predated (C. Gunn personal observations) In some cases nests at heavily visited tourist locations which are easy to see have been vandalized by humans in California, Colorado and Idaho, as noted by Foerster 1987; S.E. Hirshman personal communication; G. M. Worden personal communication.)
The vast majority of documented predation on Black Swifts involves egg, nest, and specimen collecting by humans before the 21st century.
Black Swift is more prone to mortality due to harsh environmental conditions. Typical nest placement at waterfalls and at wet locations provide inherent potential dangers to a chick if it should fall out of the nest or fledge prematurely before being capable of sustained flight or they may be washed away or their feathers become saturated and weighted with water (S.E. Hirshman personal observations). At some locations nests are lost to flash floods. Because of their dependence on aerial insects, they may be susceptible to starvation due to prolonged events of cold and wet weather as described by Donnelly (1974).