Aspects of cranial adaptation in foot-propelled diving birds – foraging and visual fields of some piscivorous species

The adaptation to an aquatic lifestyle has occurred several times during the evolution of birds. The transition from a terrestrial to an aquatic lifestyle requires enormous changes in morphology, physiology, and behaviour. In addition to many physical parameters, aquatic foraging is also a limiting factor, despite the fact that aquatic habitats are often rich in food and prey. Despite many previous studies (foraging, physiology, anatomy, ecology, etc.) and a large amount of data regarding piscivore foot-propelled diving birds, our knowledge on the possible relationships between cranial morphology, feeding mechanism, visual abilities and binocularity is still very limited. In this study, we attempt to achieve a deeper understanding of the visual abilities and foraging related attributes of 5 recent and 1 extinct species of foot-propelled diving birds. We attempted to measure the horizontal visual fields of these species using 3D visualization techniques. According to our model, the narrowest horizontal binocular field was measured in Anhinga (Anhinga anhinga), and the widest was measured in the cases of Great Cormorant (Phalacrocorax carbo) and Goosander (Mergus merganser). Our results support the prediction that binocular field variation among aquatic birds is primarily associated with foraging methods and activities.