DOI: 10.5061/dryad.0k6djhb64
title: The respiratory system influences flight mechanics in soaring birds

description: The subpectoral diverticulum (SPD) is an extension of the respiratory
 system in birds that dives between the primary muscles responsible for
 flapping the wing. Surveying the pulmonary apparatus in 68 species showed
 that the SPD was present in virtually all soaring taxa investigated yet
 absent in non-soarers. We find that this structure independently evolved
 with soaring flight at least seven times, indicating that the diverticulum
 may have a functional and adaptive relationship with this flight style.
 Using the soaring hawks Buteo jamaicensis and B. swainsoni as models, we
 show that the SPD is not integral for ventilation, that an inflated SPD
 can increase the moment arm of cranial parts of the pectoralis, and that
 pectoralis muscle fascicles are significantly shorter in soaring hawks
 than in non-soaring birds. This coupling of an SPD-mediated increase in
 pectoralis leverage with force-specialised muscle architecture produces a
 pneumatic system adapted for the isometric contractile conditions expected
 in soaring flight. The discovery of a mechanical role for the respiratory
 system in avian locomotion underscores the functional complexity and
 heterogeneity of this organ system and suggests that pulmonary diverticula
 likely have other undiscovered secondary functions. These data provide a
 mechanistic explanation for the repeated appearance of the SPD in soaring
 lineages, demonstrating that the respiratory system can be co-opted to
 provide novel biomechanical solutions to the challenges of flight and
 thereby influence the evolution of avian volancy.
description: # **README document for the dataset from**: Schachner et al., 2024. The
 respiratory system influences flight mechanics in soaring birds. Nature.
 [https://doi.org/10.5061/dryad.0k6djhb64](https://doi.org/10.5061/dryad.0k6djhb64) **Description of the data and file structure** This dataset includes the files and code used to re-run the character correlation analyses from the manuscript. It also includes the surface files that were used to model the moment arms for the biomechanical analysis of the pectoralis models of the Red-tailed and Swainson’s hawks. These models should be opened and run using GaitSym 2019. The link for this free software is listed below. Lastly, there is a zipped file of high-resolution images (TIFF image files), showing each of the birds scanned for this project. They are the original images used in the extended data section of this manuscript. The following files are provided: 1\)        Input files and code necessary to run the character correlation analyses in R. 2\)        A zipped file with the surfaces used for the MDA models. Each folder contains the MDA model file (.gaitsym) and associated OBJ graphics file for visualization of each bird. Models can be opened in GaitSym2019 available from [https://animalsimulation.org](https://animalsimulation.org). Models will not work with older versions of GaitSym. Avian names match the chart provided in the methods section of the manuscript.  3\)        A zipped file with the high-resolution images of the axial slices from the Extended Data figures demonstrating the morphology of the subpectoral diverticulum around the sternocoracoideal joint. These TIFF files are exported screen shots of single CT or µCT DICOM images of birds included in the study. The species is listed in the file name. **Sharing/Access information** All data are freely available **Code/Software** The input files and code for the character correlation analysis can be run in R. R is available here: [https://www.r-project.org/](https://www.r-project.org/) The MDA models should be run in GaitSym2019 which is available from [https://animalsimulation.org](https://animalsimulation.org)