Smart beaks: non-visual senses in birds
Most birds, like most people, 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 the three species of southern African ibises: Hadeda 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).
This project is led by MSc student Carla du Toit. In 2017, her research focused on the anatomy of the bill-tip organ in the three ibis species resident in South Africa. The bill-tip organ of probe-foraging birds is made up of mechanosensory 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.
Carla hypothesizes that there is a relationship between the morphology and histology of the bill-tip organ and the foraging ecology of ibises. Hadeda, Sacred and Glossy Ibises are ideal model species for investigating this hypothesis, because they forage in different substrate environments ranging from terrestrial to aquatic sites. Carla started the project as an MSc student at the beginning of 2017, and an upgrade to PhD was approved in November. During 2017, she sourced skeletal material of the three study species to measure and describe the sensory pits in the bony bill-tips of the birds. Carla sourced samples from South African museums and also travelled to the UK and France and visited multiple museum collections there. In addition, she was able to visit palaeontology collections to source fossil birds for the study. Carla completed µ-CT scans of two Hadeda and two Sacred Ibis specimens, using the CT scanning facility at Stellenbosch University, in conjunction with technician Dr Anton du Plessis. The data from these scans are now ready for analysis. In addition, she optimized the methods of preparation and staining of fresh tissue from bill-tips of accidentally-killed (road killed, euthanized at SANCCOB due to injury, etc.) ibises for histological study, and secured sufficient specimens of Hadeda and Sacred Ibises for this purpose. Together with Susie Cunningham, she performed a short pilot study to develop the methods to describe the specific foraging behaviours of these species in the wild.
- Carla’s registration will be upgraded to PhD level from January 2018.
- Analyses of ibis skulls showed an increase in the length of the beak that is pitted as well as the number of sensory pits with increasing use of aquatic habitat, consistent with the pattern shown in other species of ibis from other parts of the world.
- The pattern of pitting between the three species differed, with Glossy Ibises having a higher number of pits on the inside surfaces of their beaks than the other two species. This could indicate that Glossy Ibises are probing with their beaks open more often than the other species, which will be confirmed by observing wild foraging birds..
- The histological sections already performed indicate clear differences between the three species in terms of the arrangement of the sensory receptors and soft tissues within the bony pits, with Sacred and Glossy Ibises bearing a close resemblance to each other, and Hadedas being significantly different.
- At the British Natural History Museum, Carla found several specimens of fossil scolopacid birds with their beaks very well preserved. She will be comparing these to modern specimens to look for differences in the structure of the bill-tip organ over time in this family.
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 successfully, improving understanding of potential mechanisms underlying the expansion of Glossy Ibises and 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 these species. Planned comparative work on paleontological specimens will improve our understanding of the ecology of extinct birds.
DST-NRF CoE grant.
Dr Susan Cunningham (FIAO, UCT)
Prof. Anusuya Chinsamy-Turan (BioSci, UCT)
Dr Steve Portugal (Royal Holloway, U. London)
Dr Anton du Plessis (U. Stellenbosch)
Student: Carla du Toit (PhD, UCT)