Wing extension-flexion coupled aeroelastic effects improve avian gliding performance

During flight, birds instigate remarkably large changes in wing shape, commonly termed 'wing morphing'. These changes in shape, particularly extension-flexion, have been well documented to influence the production of aerodynamic forces. However, it is unknown how wing stiffness changes as a result of the structural rearrangements needed for morphing. We address this gap in knowledge through mechanical testing of in situ flight feathers in anaesthetized pigeons and found that while the most distal portion of the feathered wing remained unaffected, proximal areas saw an increase in out-of-plane stiffness due to wing folding. Following this, we used computational fluid-structure interaction simulations to evaluate how this morphing-coupled change in stiffness might modulate local flow patterns to affect aerodynamic performance. We found that flexible wings perform better than entirely rigid wings as an increase in near-wall vorticity delayed flow separation. Furthermore, an increase in stiffness in a folded wing during high-speed flight prevented the reduction in lift seen in more flexible cases caused by aeroelastic flutter modes destructively interfering with shed leading-edge vortices. Collectively, these results reveal that mechanical changes coupled with wing morphing can provide a speed-dependent mechanism to enhance flight performance.

Modification of Keratin Integrations and the Associated Morphogenesis in Frizzling Chicken Feathers

The morphological and compositional complexities of keratinized components make feathers ingenious skin appendages adapted to diverse ecological needs. Frizzling feathers, characterized by their distinct curling phenotypes, offer a unique model to explore the intricate morphogenesis in developing a keratin-based bioarchitecture over a wide range of morphospace. Here, we investigated the heterogeneous allocation of α- and β-keratins in flight feather shafts of homozygous and heterozygous frizzle chickens by analyzing the medulla-cortex integrations using quantitative morphology characterizations across scales. Our results reveal the intriguing construction of the frizzling feather shaft through the modified medulla development, leading to a perturbed balance of the internal biomechanics and, therefore, introducing the inherent natural frizzling compared to those from wild-type chickens. We elucidate how the localized developmental suppression of the α-keratin in the medulla interferes with the growth of the hierarchical keratin organization by changing the internal stress in the frizzling feather shaft. This research not only offers insights into the morphogenetic origin of the inherent bending of frizzling feathers but also facilitates our in-depth understanding of the developmental strategies toward the diverse integuments adapted for ecological needs.

Tail feather strength in tail-assisted climbing birds is achieved through geometric, not material change

Birds encompass vast ecomorphological diversity and practise numerous distinct locomotor modes. One oft-cited feature seen in climbing birds is an increase in tail 'stiffness', yet it remains unclear to what extent these feathers are altered, and the specific mechanism by which differences in functional performance are attained. We collected a broad taxonomic sample of tail feathers (6525 total, from 774 species representing 21 avian orders and ranging in size from approximately 3 g to greater than 11 kg) and present data on their material properties, cross-sectional geometry and morphometrics. Ordinary and phylogenetic least-squares regressions of each variable versus body mass were conducted to assess scaling relationships and demonstrate that tail-supported climbers exhibit longer tail feathers with a wider rachis base and tip, and a greater second moment of area and maximum bending moment. However, no differences were observed in the material properties of the keratin itself. This suggests that tail-supported arboreal climbing birds of multiple orders have independently adopted similar morphologies. Moreover, these geometric relationships follow the same allometric scaling relationships as seen in the long bones of mammalian limbs, suggesting that the morphology of these developmentally and evolutionarily distinct structures are governed by similar functional constraints of weight support.

The ornithological collection of the Zoological Museum of Babeș-Bolyai University, Cluj-Napoca, Romania - Part 1: the catalogue of bird skin specimens

This paper reviews the bird skin collection housed in the Zoological Museum of Babeș-Bolyai University, Cluj-Napoca, Romania. The collection includes 925 specimens, belonging to 193 species from 53 families and 20 orders, collected between 1859 and 2021. Due to its historical background and the presence of rare species, it is considered to be one of most important ornithological collections in Eastern Europe. Such a collection can serve as a basis for valuable ornithological studies. Furthermore, a map representation with new distribution data for bird species is provided, which represents a source of information for the status of the avifauna of the Carpathian basin in the 19^th and 20^th centuries.

Analysis and comparison of protein secondary structures in the rachis of avian flight feathers

Avians have evolved many different modes of flying as well as various types of feathers for adapting to varied environments. However, the protein content and ratio of protein secondary structures (PSSs) in mature flight feathers are less understood. Further research is needed to understand the proportions of PSSs in feather shafts adapted to various flight modes in different avian species. Flight feathers were analyzed in chicken, mallard, sacred ibis, crested goshawk, collared scops owl, budgie, and zebra finch to investigate the PSSs that have evolved in the feather cortex and medulla by using nondestructive attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR). In addition, synchrotron radiation-based, Fourier transform infrared microspectroscopy (SR-FTIRM) was utilized to measure and analyze cross-sections of the feather shafts of seven bird species at a high lateral resolution to resolve the composition of proteins distributed within the sampled area of interest. In this study, significant amounts of α-keratin and collagen components were observed in flight feather shafts, suggesting that these proteins play significant roles in the mechanical strength of flight feathers. This investigation increases our understanding of adaptations to flight by elucidating the structural and mechanistic basis of the feather composition.