Avian Volitation And Vocalization

Volitation:  Flight is surely one of birds’ most fascinating characteristics. But flightless birds like penguins and ostriches are equally fascinating, if not more so. How is it that one group evolved a high-flying lifestyle, and one didn’t? Turns out, the ways the wings and feathers of flightless birds differ from those of their airborne cousins is still not well understood. Associate Curator Jingmai O'Connor and Bass Postdoctoral Fellow Yosef Kiat shed some light on the matter in a new study in the journal PNAS. In examining hundreds of birds in museum collections, they discovered a suite of feather characteristics that all flying birds have in common, providing clues about how the dinosaur ancestors of modern birds first evolved the ability to fly, and which dinosaurs were capable of flight.Yosef, a feather expert, launched a study of the feathers of every order of living birds, examining specimens from 346 different species—flying and non-flying—in museums around the world. The researchers also examined 65 fossil specimens representing 35 different species of feathered dinosaurs and extinct birds. They found consistent traits among flying species. For instance, all the flighted birds had asymmetrical feathers, and between 9 and 11 primary feathers. In flightless birds, the number varies widely—penguins have more than 40, while emus have none. “It’s really surprising, that with so many styles of flight in modern birds, they all share this trait of having between 9 and 11 primary feathers,” says Yosef. “And I was surprised that no one seems to have found this before.” While Mesozoic birds and Microraptor have traits consistent with extant flying birds, the group known as anchiornithines deviate significantly, providing strong evidence that they were flightless. These findings will inform the ongoing debate as to whether flight evolved in dinosaurs just once, or multiple separate times. “Our results here seem to suggest that flight only evolved once in dinosaurs,” notes Jingmai, but she also acknowledges that the fossil record from the earliest stages of feathered wing evolution is scanty. Read more in the press release, at Discover Mag, or listen to J & Y discuss the research with Ira Flatow on Science Friday. Vocalization: If you’re the sort of person who can’t get enough about the syrinx—the vocal organ of birds—then you may well start doing backflips when you learn that Chad Eliason and colleagues have just produced another article on that device in Zoological Journal of the Linnean Society, hard on the tibio-tarsal joints of a paper in Current Biology on the same topic. We kid, but it’s actually quite interesting. The syrinx is a key innovation in the evolutionary history of vertebrate communication. Three major avian lineages, passerines, parrots, and hummingbirds, independently acquired both specialized syringeal structures and vocal-production learning (the ability to modify the structure of vocalizations as a result of hearing those of others); a functional relationship between the two has been proposed but remains poorly understood. In hummingbirds, the syrinx has never been studied comparatively alongside non-learning relatives in the parent lineage Strisores. In this new paper, Chad and colleagues from the University of Texas-Austin (including Research Associate Julia Clarke) describe the anatomy of the syrinx in 21 species of swifts and hummingbirds (most from FMNH) using enhanced-contrast computed tomography, which reveals structures previously unreported in the group. They also tested for correlations between syringeal and acoustic traits in a sample of hummingbirds and swifts using phylogenetically informed regressions. Swift and hummingbird syrinxes share certain morphological characteristics, and may be ancestral to Strisores. Meanwhile, certain differences in hummingbirds (a shortened trachea and tracheolateralis muscle) led to a significant negative correlation between tracheal elongation and maximum vocalization frequency—in other words, having a shorter trachea enables hummingbirds to produce high-frequency vocalizations.
February 23. 2024