Smart beaks: non-visual senses in birds
Most birds have excellent vision. This is part of what makes birds such an appealing group to study. However birds navigate their world using different senses as well. In this project, we investigate the non-visual senses of birds with a focus on tactile senses in their beaks. The main theme of the project is to understand the links between bill-tip anatomy and foraging ecology of three species of southern African ibises: Hadeda Ibis Bostrychia hagedash, Sacred Ibis Threskiornis aethiopicus and Glossy Ibis Plegadis falcinellus. These species all 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”: detection of 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 at the beginning of 2017, upgrading to a PhD at the start of 2018. Carla’s 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 at the tip of the bill. Although the general structure of the bill-tip organ is similar across all probe foraging species that possess it, there is interspecific variation in the shape and orientation of the pits and the receptors within them. The overall aim of Carla’s thesis is to use ibises as a model to investigate the link between the morphology of the bill-tip organ and the birds’ foraging ecology, and to explore whether these patterns can be extrapolated to infer information about the foraging ecology of extinct bird species.
The strong link between the morphology of the bony parts of the bill-tip organ and foraging behaviour suggests that we can use the structure of fossil beaks to infer information about the palaeoecology of extinct birds. In 2019, Carla undertook an extensive review of the bone structures of the beaks of over 500 species from all orders of extant birds. The review will allow us to establish whether we can determine the presence of a remote-touch-capable bill-tip organ in modern birds, based solely on the structures found on their beak bones. Furthermore, based on the phylogenetic position of some of the fossil specimens that Carla is studying, we may be able to make some significant conclusions about 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 2019
- Towards the end of 2019, Carla commenced training of captive Hadeda Ibises at the World of Birds in Hout Bay, habituating the birds to probe in soil-filled trays containing desirable (to ibises at least) superworms. This will allow her to investigate the functioning of the bill-tip organ under different substrate conditions. Her experiments are still underway and will allow us 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.
- Carla attended two conferences in 2019: in July she presented the results of her field work with wild ibises as a speed talk at the meeting of the Zoological Society of South Africa. In August, she presented some of her preliminary results on the link between the soft tissue histology and surface microstructure of the beak bones in modern birds at the International Symposium for Palaeohistology in Cape Town.
- Carla completed her review of modern birds’ beak bone morphology and its application to the study of the palaeoecology of fossil birds and submitted this for publication.
- She presented her work at the International Symposium for Palaeohistology held in Cape Town in July 2019, where it was well received by the palaeornithology community.
Impact of the project
This work will help us better understand the links between anatomy, morphology and behaviour in birds. From a conservation and global change perspective, it will allow a better understanding of the substrate conditions under which ibises are best equipped to forage, improving our understanding of potential mechanisms underlying the expansion of Hadedas into the south and west of South Africa, and the likely impact of the current drought and ongoing climate drying on the foraging success of this species. The comparative work on palaeontological specimens will improve our understanding of the ecology of extinct birds, and shed light on both the evolution of this unique sensory system in modern birds, and potentially alter our understanding of the morphology and behaviour of some of the earliest ancestors of large clades of modern birds.
DST-NRF CoE grant; DST-NRF CoE in Paleosciences.
Research team 2019
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)