The lungs of the finch: three-dimensional pulmonary anatomy of the zebra finch ().

The avian respiratory system has been an area of biological interest for centuries, with zebra finches () emerging in recent decades as a primary avian model organism popularized across numerous disciplines. The pulmonary system of birds is unique in that air moves unidirectionally through the gas-exchanging lung, and previous works have suggested anatomical constraints within the bronchial network that may be coupled to the inspiratory valving mechanism in Aves. We used µCT-based segmented models to visualize and describe the morphology of the zebra finch lower respiratory system and to examine intra- and interspecific differences of the bronchial tree with the phylogenetically and ecologically different African grey parrot (). Here, we show that zebra finches have highly variable lung and air sac morphology within individuals but generally do not diverge from the anatomical previously described for passerines. Additionally the parabronchi in the zebra finch lung are arranged into isolated segments between secondary bronchi, which has not been described and may be coupled with airflow patterns in this species. Both zebra finches and African grey parrots show constrained interostial distances and robust, caudally directed third ventrobronchi that may play an unexplored role in the unidirectional airflow patterns of birds.This article is part of the theme issue 'Biology of the avian respiratory system: development, evolutionary morphology, function and clinical considerations'.