Sonations in Migratory and Non-migratory Fork-tailed Flycatchers (Tyrannus savana)

Abstract

Sonations are sounds that animals produce with structures other than the vocal apparatus for communication. In birds, many sonations are usually produced with modified flight feathers through diverse kinematic mechanisms. For instance, aeroelastic fluttering of feathers produces tonal sound when airflow exceeds a threshold velocity and induces flight feathers to oscillate at a constant frequency. The Fork-tailed Flycatcher (Tyrannus savana) is a Neotropical bird with both migratory and year-round resident subspecies that differ in the shape of the outer primary feathers of their wings. By integrating behavioral observations, audio recordings and high-speed videos, we find that male Fork-tailed flycatchers produce sonations with their outer primary feathers P8-10, and possibly P7. These sounds are produced during different behavioral contexts including: the pre-dawn display, intraspecific territorial disputes, when attacking potential nest predators, and when escaping. By placing feathers in a wind tunnel, we elicited flutter at frequencies that matched the acoustic signature of sounds recorded in the wild, indicating that the kinematic mechanism responsible for sound production is aeroelastic flutter. Video of wild birds indicated that sonations were produced during the downstroke. Finally, the feathers of migratory (T.s.savana) and year-round resident (T.s.monachus) Fork-tailed flycatchers flutter in feather locations that differ in shape between the subspecies, and these shape differences between the subspecies result in sounds produced at different frequencies.

Morphology of migration: Associations between wing, and bill morphology and migration in kingbirds (Tyrannus)

“…This could particularly be the case in the kingbird species where tail length is suspected to be an honest indicator of mate quality (e.g., T. forficatus, Regosin & Pruett-Jones, 2001). Additionally, other forms of natural selection could be acting on flight morphology in species that use aerial courtship displays or engage in territorial encounters with conspecifics (e.g., T. savana; Jahn & Tuero, 2020;Gómez-Bahamón et al, 2020b), or in which sexual dimorphism may occur (e.g., T. dominicensis; Haberman, MacKenzie, & Rising, 1991).…”

“…Testing how migration shapes morphological variation among taxa requires a phylogenetic comparative framework with comprehensive inter- and intraspecific sampling. Studies comparing migratory to sedentary birds support that long-distance migration favors longer (Rayner, 1988; Wiedenfeld, 1991; Pérez-Tris & Tellería, 2001; Förschler & Bairlein, 2011; Tellería et al , 2013), and more pointed (Carvalho Provinciato, Araújo, & Jahn, 2018; Gómez-Bahamón et al , 2020b) wings for increased aerodynamics. Hypotheses that link bill morphology and migratory status are less well-studied, but hinge on differences in diet that covary with migratory status (Bell, 2011; but see Cox, 1968; Herrera, 1978; Leisler, 1990).…”

“…We used phylogenetic comparative methods to test for ecomorphological associations in wing and bill morphology among migratory, partially migratory, and sedentary kingbirds ( Tyrannus ; Fitzpatrick et al , 2004). Kingbirds are flycatchers (Tyrannidae) with considerable variation in migration status and morphology within and among species, as well as a rich body of literature linking ecology and morphology (Fitzpatrick & Schauensee, 1980; Fitzpatrick, 1981; Sherry, 1984; Fitzpatrick, 1985; Cintra, 1997; Fitzpatrick et al , 2004; Gabriel & Pizo, 2005; Carvalho Provinciato et al , 2018; Gómez-Bahamón et al , 2020b). As aerodynamic theory predicts that longer, more pointed wings and shorter tails are more efficient for long-distance migratory flights (Norberg, 1995; Pennycuick, 2008), we expected migratory taxa to have longer and more pointed wings compared to sedentary taxa (Kipp, 1942, 1958; Winkler & Leisler, 1992; Mönkkönen, 1995 and references therein; Lockwood, Swaddle, & Rayner, 1998).…”

On the Multifunctionality of Feathers and the Evolution of BIrds

“…Feathers that do produce sounds often to show abnormal shapes, though these modifications can be hard to detect (Clark et al 2016). These shapes are likely to facilitate noise production, including in the wings (Clark 2008) and tails (Clark and Feo 2008) of hummingbirds, and in the wings of pigeons (Niese and Tobalske 2016) and Fork-tailed Flycatchers (Gómez-Bahamón et al, 2020). Aeroelastic fluttering cannot explain all feather sounds in birds however, some groups of birds produce sound with feathers that appears to not involve aeroelastic flutter through wing clapping or fluttering.…”

Molecular phylogenetics of Doraditos (Aves, Pseudocolopteryx): Evolution of cryptic species, vocal and mechanical sounds

“…The over 400 species of Neotropical tyrant flycatchers (Tyrannidae) exhibit a wide array of communication signals, including the spectacular plumage and bare red throat of the vocally unassuming Strange‐tailed Tyrant ( Alectrurus risora ), the highly vocal drab cryptic species in the genera Empidonax , Elaenia and Serpophaga , and the production of mechanical sounds during display flights in the genera Tyrannus , Knipolegus and Pseudocolopteryx (Fitzpatrick et al., 2004; Gómez‐Bahamón et al., 2020; Johnson & Cicero, 2002; Jordan & Areta, 2020; Rheindt et al., 2015; Straneck, 1993). Vocalizations are innate in the family (Amador et al., 2008; Kroodsma, 1984; Kroodsma & Konishi, 1991), but nothing is known on the ontogeny of sonations (i.e.…”