The vocal organ of hummingbirds shows convergence with songbirds

Abstract

among these very closely related species may be reflected in their peripheral vocal organs. Here we show that recent speciation includes divergence in the anatomy of their vocal organs. Methods Animals. We investigated syrinx histology and morphology in Anna's hummingbirds (ANHU, Calypte anna), Costa's hummingbirds (COHU, C. costae), rufous hummingbirds (RUHU, Selasphorus rufus), and black-chinned hummingbirds (BCHU, Archilochus alexandri) for a total of 18 hummingbirds. A summary of species and sex is provided in Supplementary Table 1. A single male ANHU was salvaged immediately following a window collision and used for whole-body microCT imaging (Fig. 1c,d), and a separate group of ANHUs were used for vocal recording (N = 3) and not used for histological or morphological comparisons. We captured all four species in Cochise, Pima, Maricopa, Gila and Coconino Counties (Arizona) during the months of June-August of 2016-2017 under permits from the Arizona Department of Game and Fish and the US Fish and Wildlife Service. All procedures were approved by the Institutional Animal Care and Use Committee at Midwestern University, Glendale, AZ, USA (IACUC Nos. 2818 and 2892) following established guidelines for use of wild birds in research 30 .

High-frequency hearing in a hummingbird

“…Our results suggest that hummingbirds producing HF vocalizations ( 4 , 35 ) have evolved adaptations for the production and perception of HF sounds, which may not be present in other birds. Recently, two independent research groups ( 36 , 37 ) reported on the unusual position of the avian vocal organ, the syrinx, in hummingbirds. While in most birds the syrinx is located inside the thoracic cavity, hummingbirds have a syrinx that is located outside the thorax, a feature that we have also observed in O. chimborazo .…”

“…While in most birds the syrinx is located inside the thoracic cavity, hummingbirds have a syrinx that is located outside the thorax, a feature that we have also observed in O. chimborazo . The position of the syrinx ( 36 ) paired with other musculature differences ( 37 ) may change the mechanical properties of the vocal organ and air pressure while vocalizing, facilitating the production of HF sounds. In some species of hummingbirds, which have also encountered environmental pressures to avoid signal masking in acoustically challenging environments ( 4 ), these conditions may have come together to promote the evolution of HF vocalizations as part of the vocal repertoire of these species.…”

The hummingbird syrinx morphome: a detailed three-dimensional description of the black jacobin’s vocal organ

“…Within hummingbirds, a comparative study that included the syrinx of the clades Hermits, Mangoes and Brilliant suggested that adjacent bronchi, highly modified bronchial halfrings, intrinsic muscles and tympanic ossicle are unique to hummingbirds within Apodiformes [35]. A recent study that investigated the syrinx of the clade Bees, relatively recent radiation within hummingbirds [34], found also specialized pairs of accessory cartilages, one of them embedded in the medial vibratory membranes, and intrinsic muscles [40]. Similarly to hummingbirds, the syrinx of the swifts is tracheobronchial with an osseous tympanum [41].…”

“…The extrathoracic disposition of the syrinx and accompanied absence of STs in hummingbirds [35,40,52], might have been one of the driving pressures for the evolution of intrinsic muscles, a key prerequisite of vocal learning.…”

Anatomical, Histological, and Electron Microscopic Structures of Syrinx in Male Budgerigars (Melopsittacus undulatus)

“…The skeleton of the syrinx is formed by four cartilaginous compartments; the cranial (tympanum) cartilaginous rings, the intermediate cartilaginous rings, the caudal (bronchosyringeal) cartilaginous rings, and the pessulus, at the tracheal bifurcation (King, 1975; King & Mclelland, 1984; Ragab et al, 2016). Passerine vocal organ has four structures: (a) a group of intrinsic muscles, (b) a large tympanum, (c) the presence of accessory cartilages, and (d) the presence of two sets of opposing soft tissue membranes (Riede & Olson, 2020). The intrinsic muscle cells play a role in generation of sound by affecting the tension of the medial tympaniform membranes (Frank et al, 2006).…”