2005/01/01 by Andrew Farnsworth · 2 citations
Biochemistry, Genetics and Molecular Biology · Agricultural and Biological Sciences · #Animal Vocal Communication and Behavior #Plant and animal studies #Animal Behavior and Reproduction
paper · pdf · doi:10.1642/0004-8038(2005)122[0733:fcatvf]2.0.co;2
openalex publication_date 2005/01/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/29
Many passerine birds and their relatives utter flight calls, species-specific vocalizations given primarily during sustained flight, especially during migration. References to flight calls appeared in the ornithological literature as early as the 1890s, but some of the most basic features of these calls remain poorly known, including their functions, origins, ontogeny, distances over which they are used, and how much individual variation exists in the characters of the calls and their rates. With improved knowledge of these vocalizations, flight calls possibly will have a variety of applications. Identifying their function could illuminate how birds refine migration strategies during crucial decision-making periods. Because flight calls are relatively simple vocalizations, compared with many others that birds use, they provide useful characters for future evolutionary and comparative analyses. Monitoring flight calls can be a powerful method for studying nocturnal migration. However, such applications require more detailed knowledge of flight-calling behavior. Here, I summarize the available information on flight calls and high-light areas where future research may improve and expand this knowledge. Flight calls of passerines, as well as cuckoos and woodpeckers, among others, are defined as species-specific notes, either frequency-modulated or pure, of up to several syllables that generally are in the 1–9 kHz frequency band and 50–300 ms in duration. Spectrograms of representative passerine flight calls are shown in Figure 1. These calls are the primary vocalizations given by many species of birds during long, sustained flights, particularly migratory flights (Evans and O'Brien 2002). Despite the name “flight” call, birds may produce these calls in several contexts other than migration, including while perched (notably the cardueline finches; Mundinger 1970) and while interacting with fledged young (notably parulid warblers; A. Farnsworth pers. observ.). Many species also utter flight calls year-round (Evans and O'Brien 2002), and some regularly give them while flying during the day (e.g. Yellow-rumped Warbler [Dendroica coronata]; Evans and O'Brien 2002). Flight calls are distinct from songs and, more importantly, they are distinct from other types of short calls, such as “chip” notes and alarm calls. Examples of passerine flight calls (from Evans and O'Brien 2002): (A) Bobolink (Dolichonyx oryzivorus), (B) Indigo Bunting (Passerine cyanea), (C) Blackpoll Warbler (Dendroica striata), and (D) Swainson's Thrush (Catharus ustulatus). Note that the axes of these spectrograms have identical scales, which facilitates comparing the different species' calls. (B) and (C) depict modulated calls, whereas (A) and (D) depict flight calls or parts of flight calls with pure tones Flight calls have been studied most intensively in North America, and Evans and O'Brien (2002) compiled a guide to the flight calls of migratory birds that occur in the eastern part of the continent, mostly east of the 100th meridian. This unique resource provides detailed information on flight calls, including descriptions of the vocalizations and calling behavior, spectrographic representations, examples, and identification tips. Not all of the species contained in the guide regularly give flight calls, and not all of those that regularly give flight calls utter them at night. For example, cuckoos, woodpeckers, corvids, larks, swallows, thrushes, wood-warblers, tanagers, grosbeaks, emberizid sparrows, blackbirds, and finches (among other groups) give flight calls regularly, but most woodpeckers, corvids, larks, swallows, and finches rarely call at night (these are primarily diurnal migrants). Groups of species that do not regularly give flight calls when moving during day or night include New World flycatchers (Tyrannidae), vireos (Vireonidae), and mimids (Mimidae). Although less intensively studied than Nearctic species, numerous Palearctic and Paleotropical species also utter flight calls (Chappuis 1989, van den Berg et al. 2003). Some of these are closely related to vocal New World species, such as Turdus thrushes (e.g. Fieldfare [Turdus pilaris]; Redwing [T. iliacus]), cardueline finches, pipits, and Regulus crests; other species are more typically Old World, such as bee-eaters (Meropidae), Emberiza buntings (e.g. Rustic Bunting [Emberiza rustica], Ortolan Bunting [E. hortluna]), many wagtails (Motacillidae), larks (Alaudidae), and fringillids. Like some Nearctic birds, not all those species regularly vocalize at night. In fact, it is primarily European Turdus thrushes (Siivonen 1936; Browne 1953; Vleugel 1954, 1960; Chappuis 1989; van den Berg 2003) and some Emberiza buntings and Regulus crests (M. Robb pers. comm.) that regularly give flight calls during nocturnal migration. Other Palearctic-Paleotropical species also give flight calls at night, including several species of pitta (Fairy Pitta [Pitta nympha], S. Lin pers. comm.; Blue-winged Pitta [P. moluccensis], P. Round pers. comm.), some Asian and Australo-Papuan cuckoos such as Long-tailed Koel (Eudynamys taitensis) and Pied Cuckoo (Clamator jacobinus) (N. Olliver pers. comm.), and Woodland Kingfisher (Halcyon senegalensis) (D. Mostert pers. comm.). Research in Africa, Asia, and Australia will probably identify numerous additional species that utter flight calls at night. Like New World exceptions that rarely give flight calls, there are also Palearctic species that rarely give flight calls: Old World flycatchers (Muscicapidae) and Old World warblers (Sylviidae) are generally silent during migration. However, Pied Flycatchers (Ficedula hypoleuca) and Spotted Flycatchers (Muscicapa striata), which are not normally heard during nocturnal movements, apparently vocalize when visibility is poor (B. Bruderer pers. comm.; see Herremans 1993), and some sylviid warblers infrequently vocalize (similar to fledgling calls) during daytime movements (Blackcap [Sylvia atricapilla] and Chiffchaff [Phylloscopus collybita], M. Herremans pers. comm.; River Warbler [Locustella fluviatilis], J. Kriek pers. comm.). How are calling birds identified when they are migrating at night and not visible? Identification of some calls is simple, because the nocturnal vocalizations are the same as the diurnal ones (Catharus spp.; Howes 1912, Evans 1994). However, identification of many species is often more complicated and requires additional information, which generally comes from two distinct sources (Evans and Mellinger 1999, Evans and Rosenberg 2000): (1) Comparisons of spectrograms of diurnal flight calls of known species and unknown nocturnal flight calls—many birds observed in visible morning flights often give flight calls (Evans and Rosenberg 2000, Evans and O'Brien 2002; see Gauthreaux 1978, Hall and Bell 1981, Wiedner et al. 1992 for descriptions of the morning flight phenomenon). Also, direct comparison is possible of unknown nocturnal vocalizations and flight calls recorded from birds in captivity or from birds carrying miniature microphones (Hamilton 1962, A. Cochran and M. Lanzone unpubl. data, W. Cochran unpubl. data). Figure 2 shows examples of these types of comparisons. (2) Correlating the seasonal timing and geographic range of nocturnal calls with known timing and migration ranges for each species—species-specific migration calendars are available for many species and locations in North America, often generated from accounts of species killed at night in collision with television towers, lighthouses or buildings, and historical arrival and departure dates (see Evans 1994, Evans and Rosenberg 2000; see also Hedges 2001). Flight calls of American Redstart (Setophaga ruticilla): (A) diurnal flight call, (B) nocturnal flight call, and (C) flight call recorded in captivity. Note similarities among the calls, such as their basic V-shaped pattern; however, also note that calls vary individually, such as in the depth and shape of their characteristic V-pattern Ornithologists debated certain aspects of bird migration strategies and patterns into the late 19th and early 20th centuries—for example, whether birds migrate across the Gulf of Mexico (Frazar 1881; Cooke 1904; Lowery 1945, 1946; Williams 1945, 1947)—but most accepted that many species migrate at night (Chapman 1888; Cooke 1904, 1915; Lowery 1946). It was largely the flight calls of migrating birds that authors cited as direct evidence of such nocturnal movements, and they used the calls to identify species, to assess the magnitude of migration, and as a quaint reminder of the wonders of bird migration. Libby (1899) tallied 3,600 calls during five hours of passive listening near Madison, Wisconsin, on 14 September 1896, the first published attempt to quantify nocturnal migration using flight calls. Kopman (1904) and Carpenter (1906) referenced thrush vocalizations heard during nocturnal migration, especially of the Veery (Catharus fuscescens) and Gray-cheeked Thrush (C. minimus), and Thayer (1903) similarly referenced the vocalizations of Black-billed Cuckoo (Coccyzus erythropthalmus). Howes (1912) detailed the flight calls of Swainson's Thrush (C. ustulatus) in terms of location and timing of its migratory routes in autumn in the northeastern United States. Tyler (1916) highlighted the diversity of flight calls and also noted that they appear in a species' vocal repertoire during periods of migration. Studies through the 1950s illuminated the temporal pattern of nocturnal calling (e.g. Turdus spp. in Finland [Siivonen 1936] and Ireland [Browne 1953], and Catharus spp. in the Gaspé Peninsula [Ball 1952; one of the most comprehensive studies on the timing of migration of a particular species through a region using flight calls]). Popular accounts of nocturnal call counts from eastern North America also appeared regularly, usually as call totals or interpreted numbers of Catharus thrushes passing over during a portion of an evening (Audubon Field Notes; see brief summary in Evans and O'Brien 2002). Toward the end of the 1950s, interest in quantifying nocturnal migration sparked a new debate about the relationship between the timing of peak bird density aloft and the timing of peak flight-call counts. The relationship between flight-call counts and direct visual observations of migratory birds passing in front of the full moon (Lowery and Newman 1955, Newman 1956) suggested that calling peaks at a different time than the density of birds in the atmosphere: bird density peaked 2–3 hours after sunset (Lowery and Newman 1955, Newman 1956), whereas vocalizations peaked in the hours just before dawn (Ball 1952). Also, visual observations indicated that the distribution of nocturnal migrants in the air was relatively even, in contrast to flight-call data that suggested a clumped distribution (Ball 1952). To some, the record of nocturnal calling exaggerated the impression of large-scale migration detected by moon-watching (Vleugel 1960). To confound the situation further, data from European call counts indicated that calling by Turdus spp. peaked close to local midnight and spiked again just before dawn (Vleugel 1954, 1960). The interpretation of the acoustic record, especially in relation to actual numbers of birds aloft at night, was not at all clear. Although the limits and variability of human hearing largely prevented objective comparisons among earlier studies of migration, technological developments of the 1940s and 1950s enabled researchers to make audio recordings of nocturnal bird migration that were useful for more efficient and objective data collection, analysis, and comparisons (see Evans and O'Brien 2002). The invention of the sound spectrograph made visual comparisons of similar sounds possible (Koenig et al. 1946), and the perfection of magnetic tape and tape-recording devices made archiving of sounds a reality. Graber and Cochran (1959) sampled nocturnal flight calls using a microphone and a parabolic antenna, automatically recording calls to magnetic tape at 10-min intervals during entire nights of migration. Such techniques provided the foundation for future, in-depth examination of aural records of nocturnal migration. Graber (1968) further advanced these techniques by comparing the acoustic record of nocturnal migration with radar and diurnal field-census data. However, the meaning of the acoustic record of nocturnal migration remained equivocal (Graber 1968), though Graber and Cochran (1959, 1960) suggested that qualitative data from acoustic monitoring complemented quantitative data from visual methods. The function of flight calls was still unknown, though Hamilton (1962) presented evidence from birds recorded in captivity that suggested that calls facilitated communication among individuals in flocks. Although electronic technologies made acoustic sampling possible across increasingly large temporal and of migration, data and analysis, and recording and and often recording devices the of acoustic However, by the late and early more and (see for researchers to many that to to nocturnal migration. recorded nocturnal flight calls automatically at using a by of and This method audio tape and of the night when there was and pers. A. J. pers. comm.) provided the to flight calls automatically from either made recordings or data from an This generally nocturnal flight calls by temporal peaks in a frequency range and calls by over time with an in of spectrographic et al. and and et al. enabled more examination and of similar calls. and microphone by Evans 2000; Evans and Mellinger facilitated of flight-call data across geographic and temporal (Evans and Rosenberg 2000, pers. radar technologies and the to of nocturnal migration at much Graber et al. Farnsworth et al. Identification of flight calls also and in the of the first electronic identification guide (Evans and O'Brien 2002). between call counts and are from the literature and to in the during of calls with and especially and Graber Graber and Cochran Graber 1978, Evans and Mellinger counts also as birds between air of different density 1956), where for as and poor birds to up or (Graber and Cochran 1960). usually during periods of (Graber and Cochran 1960). Vleugel that call counts of Turdus in during autumn with the of and counts are also with of in whereas the is in the (Graber and Cochran 1960). when from the of these the studies and there is information about of calling and their relationship to of bird The of on calling are poorly Evans recorded many vocalizations of the during autumn migration (see also Evans and Rosenberg and Evans indicated that flight of calling were less than those of calling thrushes to is also temporal variation in the of calling birds, and may be or on different nights W. Evans pers. comm.). It is not known whether calling is primarily a in the close to the Although migration across (Lowery and Newman 1955, Gauthreaux et al. evidence that features such as or and birds Bruderer 1978, Williams et al. these features also appear to flight calls. Evans and Mellinger that in in numbers of calls on the of birds migrating the and to over the Gulf of these birds up on the and Evans that when the is of the flight of calling and calling birds in areas of Despite the variability in all these patterns of call counts across and are often and probably some and patterns (e.g. the migration timing of different temporal patterns of calling are much more These patterns could and additional unknown and recorded of thrush vocalizations in the hours just before with a of calls after midnight to call before midnight (from Graber and Cochran this though they detected migration at of the night, but a peak in calling in the hours before dawn migration all night. Farnsworth and a similar pattern in an acoustic of migration over the Gulf of that the peak of call counts in the two hours just before call counts of Turdus in usually peaked in the hours to local with from this pattern usually with the of a front (Siivonen 1936; Browne 1953; Vleugel 1954, 1960). flight-call counts have the night, though on many peaks in the hours close to local midnight et al. Farnsworth et al. for the variability in peak call counts are not known, but they include (Graber and Cochran Graber Evans and Mellinger 1999, Evans and Rosenberg 2000, Evans and variation in and species Hamilton 1981, Farnsworth et al. Some variability from different species at different of the night and calling at different during (Graber of calling may vary among The call counts for Swainson's microphones from to including one individual and one individual that not call for Cochran pers. comm.). but pattern is by all by migrating birds in the Palearctic to a different pattern than in the Nearctic migration are more at and by more species in the New this is a function of in the European between the migration or some is accounts from numerous European researchers that flight calling is in the species that regularly vocalize at night Vleugel and 1952). have suggested that birds give flight calls in to or the of dawn (Ball 1952). In some species, flight calls may the of a individual in a (e.g. [T. M. Robb pers. comm.). Other that some flight calls in though this is apparently Farnsworth pers. The flight calls for in with visual information, especially at night and and but this is not known in The from the with that flight calls to and migratory or in especially in birds 1952; Hamilton Graber 1981, (Dolichonyx oryzivorus), Hamilton (1962) that calling from birds in and was with migratory and and Flight calls also among and, at in some species, of individuals and Mundinger Mundinger 1981, et al. et al. the calls of migrating birds function in the same is not whether birds call in a that is similar to that of calls and alarm calls, for and is also unknown and and and 2000, et al. et al. may also be by flight calls than and alarm calls (Lowery and Newman Graber and Cochran 1960; Hamilton 1962, Gauthreaux during nocturnal migration (Graber and Cochran Hamilton 1962, Evans and Mellinger 1999, Evans and Rosenberg however, may be or from that could such Although the of for nocturnal migrating birds may flight calls for to of and to by and monitoring (Lowery and Newman and 1981, Such could be especially useful when visibility is the of hearing others, and (Graber and et al. This could be particularly for evidence that young birds vocalize more than Cochran pers. comm.). Many flight calls a pattern of frequency that may be for birds information with some and patterns for sound or and The to calls of other individuals as a function of and and (Hamilton which also many flight calls. birds can in frequency (e.g. and and et al. et al. and and are in of flight-calling behavior. To its to its evolutionary and patterns of over time Although flight calls are one of the calls to appear in the repertoire of cardueline finches these species and these calls by this pattern in other Hamilton (1962) suggested that the calls were the flight calls of birds with diurnal and nocturnal vocalizations of birds could provide some detailed seasonal pattern of flight calls is and a for many species be the of flight calls is crucial for to them and for their flight calls are in a of passerines, the of and may an in their studies that different species of birds have different for in et al. as well as different hearing and and in the of species could in variation in call Flight calls may also be to different related to information to on of and distribution of are that vocalizations, and these vary with among 1955, and How these to the and function of flight calls is not Also, Hamilton (1962) not that a in flight calls, and evidence that calls individuals to Flight calls, which have similarly and short may be used to information the frequency of et al. these calls are related in some to fledgling vocalizations (see Tyler there may be a direct relationship between such and flight calls. one studied the range of distances over which birds through flight calls. Because the of of communication are and et al. 2002), the of these calls that they may be used primarily for communication over short However, the with sound during flight are not known, though they have for nocturnal communication and the of nocturnal communication using certain could shape flight vocalizations that either in and or and et al. and 2003). variation in flight calls is not a (Ball but the of this variation in call such as et al. Evans and O'Brien et al. that the of certain species' flight calls, those of thrushes, larks, pipits, and finches, vary (Evans and O'Brien M. Robb pers. W. Cochran unpubl. data). The of such variation are also unknown, though Mundinger suggested that and could be studies have the of in songs (e.g. et al. 2003) and calls (e.g. and but species are and of these studies flight calls. exists in flight calls, the relationship between it and the diversity of related species is not Flight calls may be useful characters for comparative among Farnsworth and in species and et al. et al. However, variation in flight calls and the sampling of and temporal of flight-call data are to such et al. Flight calls may also on and For example, in and Farnsworth and for on flight-call in This pattern from the pattern in birds that vocalize at are also and powerful applications for monitoring flight calls to front patterns of species-specific nocturnal movements and distribution of calling migrants 1952; Graber and Cochran 1960; Graber Evans 1994, 2000; Evans and Mellinger Evans and Rosenberg and to identify the of of calling migrants Evans pers. comm.). of nocturnal bird migration as detected by radar and acoustic do not though these illuminate are in patterns of et al. et al. Farnsworth et al. call counts of migrating birds can be useful as of nocturnal bird density aloft et al. Farnsworth et al. though variation in calling and among a for bird density from flight calls Graber 1989, Evans and Mellinger 1999, Farnsworth Farnsworth et al. there can be between a of migration and of calling (Graber and Cochran et al. Farnsworth et al. detailed studies of nocturnal migration using radar and acoustic and studies that and temporal scales, will be to these studies using on flight-call counts will a of departure and arrival data as well as of species on different Many additional remain and future studies of flight calls will be however, they also will provide to improve of migration and and the these to such a behavior. are some species silent during nocturnal the of flight calls related to other such as birds migrating in similar at similar of vocalizations (Hamilton 1962, Graber 1981, birds from calling by with and, after by on the (see Hamilton are numerous applications for flight calls in and evolutionary variation in flight-calling could be the of on a migratory (e.g. flying in or whereas variation in flight-calling is possibly the of of migratory in of the or the it be that the interpretation of flight-call counts or calling could be of such information (Graber Evans and Mellinger to W. A. and M. Lanzone for to or data and from of America to W. Hamilton S. S. M. J. M. M. and the Field and in for to J. J. and their P. and M. for for this research was in part by a from and of and