Flight Vocalizations and Displays of Adult Chimney Swifts (Chaetura Pelagica): Description and Function

The vocalizations of many songbirds have been well documented and analyzed, but less is known about the vocal behavior of many non-passerines, including swifts. While flying alone as well as during aerial displays with conspecifics, Chimney Swifts (Chaetura pelagica) often utter a twitter call consisting of a series of high-frequency chip notes. However, little is known about the possible function(s) of swift flight displays and their twitter call. My objectives were to record, analyze, and document the aerial behaviors and associated vocalizations of adult Chimney Swifts. I studied swifts at the Blue Grass Army Depot in Madison County, Kentucky, where they used abandoned, concrete shelters for roosting and nesting. Camcorders were used to record swift behavior and vocalizations during the 2008 and 2009 breeding seasons (April – September). I examined possible variation in the characteristics of swift vocalizations and the frequency of different aerial behaviors among breeding stages and behavioral contexts. Chimney Swifts engaged in more interactive pair flights during the nest-building/egg-laying stage, when females are likely fertile, than any other stage, and significantly more than during the pre-building and nestling stages. This indicates importance of pair flights in courtship, pair bonding, pair synchronization, and possible mate-guarding. This study also supports the physiological synchronization and pair bond maintenance hypothesis of V-ing (a raised wing display) because the display occurred more frequently during close chases involving two birds. Interactive group flights were more common during the post-fledging stage, indicative of the presence of newly fledged young that may fly in familial groups during the day. I separated the typical swift twitter into two bouts: “steady” bouts and “quick” bouts. Mean chip rates were higher for the quick portion of the call; however, there was no biological difference in the use of steady and quick bouts among nesting stages or detailed behavioral context. Mean chip rates for quick bouts were highest for single birds and lowest for two and three birds. This supports the hypothesis that twitter calls function to provide information about a bird’s location; to help coordinate movements while flying near others (e.g. when foraging and during chases), Chimney Swifts may slow down their calls to increase the likelihood that they are heard, therefore reducing the possibility of overlapping calls with other swifts. This apparent coordination of non-overlapping notes is similar to duetting that occurs in other swifts and may be important for reproductive synchronization, pair-bond consolidation, and territory defense. I was unable to identify individual swifts; such identification would facilitate the investigation of variations in call characteristics of different birds (e.g. chip rate, steady/quick bout rate) as well as relationships between and among swifts engaging in different activities and flight displays