Ducks, dispersal and disease
In this programme we use a combination of count data, satellite telemetry, tissue samples, and molecular methods to understand the complex inter-relationships between landscape heterogeneity, wetland dynamics, the movements of waterfowl, the bird communities in which our study species occur, and the occurrence of pathogens and parasites.
Movement is a dominant theme in evolution, biogeography, community ecology, conservation and management. Southern African waterfowl, with their high movement capability and semi-nomadic lifestyle, provide an intriguing test case for understanding poorly known elements of movement ecology. Despite decades of ringing and counting efforts, little is known about the causes and consequences of the long-distance movements of most southern African ducks.
Uncertainties over the nature and frequency of waterbird movements create challenges for waterfowl conservation and management, as well as the health of South Africa’s poultry stocks and ultimately human health and wellbeing. If a virulent pathogen such as the H5N1 strain of avian influenza were to enter southern Africa, how far and how fast could wild birds carry it? And what burden does avian malaria place on bird populations that may already be stressed by habitat modification and climate change?
Since 2007, the Fitz has been working on improving our understanding of the movement ecology of waterfowl and the epidemiology of their pathogens. Tracking data for Red-billed Teal Anas erythrorhyncha and Egyptian Geese Alopochen aegyptiaca have allowed us to address questions of habitat selection, environmental drivers and scales of waterfowl movement. Our results highlight the importance of agricultural habitats in meeting the life history needs of ducks. We can also test how these birds balance trade-offs between using habitats that are safe from predators and those that provide high quality forage. Rainfall and primary productivity seem to be the dominant environmental drivers of both teal and goose movements.
We have also been investigating the influence of the composition of bird communities on the prevalence of avian malaria (Plasmodium and Haemoproteus). These blood parasites infect a wide range of bird species but the community dynamics of infection patterns are poorly known. One of the challenges is to summarise the community in a way that makes sense for the epidemiology of the parasite – grouping birds according to their capacity to introduce or maintain the disease. Fundamental questions on the relative importance of birds’ life-history traits (e.g. reproductive rate, development rate, lifespan) and behaviour (e.g. foraging, roosting and movement ecology) in explaining differential infection risks of bird species are being investigated. We have used network analysis to assess the vulnerability of the Ostrich Struthio camelus production network to outbreaks of avian influenza.
Extending our focus beyond disease, we have investigated how waterbird movement may affect other aspects of aquatic ecology. Waterbirds often disperse propagules of aquatic plants and invertebrates, which is important for colonising isolated aquatic systems and for maintaining genetic continuity among populations. Samples collected from multiple waterbird species across three wetland sites in South Africa confirm that waterbirds have a high capacity for dispersing seeds and invertebrates, either transported attached to feathers or passing through the gut. In some cases over 80 seeds have been germinated from a single faecal sample. We have also conducted experiments with captive waterbirds to gauge the time taken for seeds to pass through the digestive tract and which seed traits facilitate their survival through the gut. Dispersal of aquatic invasive species by waterbirds is plausible (especially for invertebrates) and has to be considered when managing these invasive species.
Although this programme is currently winding down following Graeme Cumming’s move to Australia, we are still tracking several Egyptian Geese as part of a translocation experiment; and several additional publications are either planned or under review.
- This programme produced 9 peer-reviewed journal articles during 2016.
- Dominic Henry graduated with his PhD in June 2015 and has since published papers from his thesis chapters in Movement Ecology, Ecosphere and Landscape Ecology
- Chevonne Reynolds submitted her PhD at the end of 2015 and graduated in June 2016. After a large amount of field work and data collection, Chevonne has published six related papers (two in Diversity Distributions, two in Freshwater Biology and one each in African Zoology and Basic and Applied Ecology).
- Eléonore Hellard has been working on the complex interrelationships between bird communities and haematozoon parasties ('avian malaria'). Communities rich in ecological functions favour disease and she has found evidence that the prevalence of more pathogenic parasites is primarily driven by host susceptibility, while that of less pathogenic parasites is primarily driven by host exposure. Some of this research has been published in Ecosphere.
- Marcela Espinaze’s 2015 CB MSc project on tick-host interactions showed that juvenile ticks are more generalist than adults and that evolutionary history can constrain host breadth. This research was published in Parasitology.
- Graeme Cumming and collaborators completed a major review of waterfowl breeding patterns across southern Africa. They identified five major breeding patterns in African waterfowl and found support for the hypothesis that juvenile food availability and predation pressure drive the timing of reproduction in these species. This research and the accompanying data set of ca 22 000 nest records are published in the open access journal Ecology and Evolution.
DST-NRF CoE grant; University of Cape Town Research Committee.
Prof. Graeme Cumming (FIAO, UCT)
Dr Celia Abolnik (University of Pretoria)
Dr Alexandre Caron (Cirad, Harare)
Dr Nicolas Gaidet (Cirad, Montpellier)
Dr John Grewar (Veterinary Services, Elsenburg)
Dr Ivan Horak (Onderstepoort, U. Pretoria)
Dr Eléonore Hellard (Biological Sciences, UCT)
Prof. Jeffrey Peters (Wright State University)
Students: Dominic Henry (PhD, UCT), Chevonne Reynolds (PhD, UCT)