Smart beaks: non-visual senses in birds
Most birds have excellent vision, which is part of what makes birds such an appealing group to study. However, birds also use other senses to navigate their world. This project investigates the tactile senses in their beaks to understand the links between bill-tip anatomy and foraging ecology. The main focus is on three species of southern African ibises that forage in different habitats. All three have a honeycomb pattern of pitting in the bones of the bill tips, which suggests they should be able to forage using the sixth sense “remote touch”, detecting small vibrations made by prey as they burrow or swim through the foraging substrate (soil, mud or water).
Carla du Toit started this project as an MSc student in 2017, upgrading to a PhD in 2018. Her research focuses on the anatomy of the bill-tip organ in probe-foraging birds, including modern ibises and extinct species in the paleontological record. The bill-tip organ of probe-foraging birds is made up of mechano-sensory receptors embedded in densely clustered pits in the bone of the bill tip. Although the general structure of the bill-tip organ is similar across all probe foraging species that possess it, there is variation in the shape and orientation of receptors among species. Carla uses three ibises as a model to investigate the link between the morphology of the bill-tip organ and the birds’ foraging ecology: Hadeda Ibis Bostrychia hagedash, Sacred Ibis Threskiornis aethiopicus and Glossy Ibis Plegadis falcinellus.
She also is exploring whether these patterns can be extrapolated to infer information about the foraging ecology of fossil birds. If there is a strong link between the morphology of the bony parts of the bill-tip organ and foraging behaviour, we can use the structure of fossil beaks to infer information about the palaeoecology of extinct birds. In 2020, we published an extensive review of the bone structures of the beaks of over 500 species from all orders of extant birds. This established that we can determine the presence of a remote-touch-capable bill-tip organ in modern birds solely from the structures of their beak bones. Using this knowledge, we have been able to infer the foraging ecology of some of the most basal members of the avian family tree, shedding light on some contentious questions regarding the evolution of modern birds.
Activities in 2020
- Our UCT team (Carla, Susie Cunningham and Anusuya Chinsamy-Turan) published one of Carla’s thesis chapters on the beaks of fossil birds. Based on the extensive review of all orders of modern birds’ beaks, we developed a classification system for beak tactile specialities and used this to study the beaks of the lithornithids, a group of fossil paleognathous birds related to modern ratites (ostriches, rheas, kiwis and allies). The lithornithids were medium-sized, flying birds that are the earliest known members of the Paleognathae. They evolved over 65 million years ago in the Cretaceous period, when non-avian dinosaurs still walked the earth. Our results suggested that these ancient birds were able to use remote-touch to locate buried prey in a similar way to modern day ibises. This finding helps to explain the mysterious presence of a structurally similar bill-tip organ in all modern paleognathous birds (which, aside from the kiwi, do not probe forage for food) as a vestigial trait inherited from a long extinct common ancestor. Indeed, based on evidence from the fossil record, we believe that this trait may have evolved even earlier in non-avian theropods.
- Despite disruptions caused by the COVID-19 lockdown in March, Carla managed to finish her experiments with captive Hadeda Ibises at the World of Birds in Hout Bay, observing the birds as they probe in soil-filled trays containing desirable (to ibises at least) superworms. These experiments will allow her to gain detailed information on the use of remote-touch by Hadedas, and to determine to what extent their foraging success is affected by the levels of soil water, which will potentially lead to a better understanding of the recent range expansion of Hadedas across southern Africa.
- Our paper on the remote-touch capability of lithornithids was published in December 2020 in the prestigious journal, Proceedings of the Royal Society B. The paper has been downloaded over 900 times in two months, which is very high for restricted access articles.
- The paper has been featured in over 30 newspaper and magazine articles internationally, including some of the biggest in science and news media, such as New Scientist and The New York Times. More features are still being written, with upcoming features in New Zealand Geographic and African Birdlife magazines. Its Altmetric Attention score, a measure of how much people are talking about the paper on social media and news outlets, places it in the top 99th percentile of the more than 16 million research outputs tracked by Altmetric.
Impact of the project
This project helps us to better understand the links between anatomy, morphology and behaviour in birds. From a conservation and global change perspective, it allows a better understanding of the substrate conditions under which ibises are best equipped to forage, improving our understanding of potential mechanisms underlying the range expansion of Hadedas into the south and west of South Africa, and the likely impact of drought and ongoing climate drying on the foraging success of this and other ibis species.
The comparative work on palaeontological specimens has improved our understanding of the ecology of extinct birds, and shed light on the evolution of this unique sensory system. By changing our understanding of the morphology and behaviour of some of the earliest ancestors of large clades of modern birds, our findings have shed light on a major sensory ecological trend in the evolution of modern birds and dinosaurs.
DSI-NRF CoE grant; DSI-NRF CoE in Paleosciences.
Research team 2020
Dr Susan Cunningham (FIAO, UCT)
Prof. Anusuya Chinsamy-Turan (Biological Sciences, UCT)
Dr Steve Portugal (Royal Holloway, U. London)
Dr Anton du Plessis (U. Stellenbosch)
Student: Carla du Toit (PhD, UCT)