Sociable Weaver nests as a resource
This project examines the importance of Sociable Weaver Philetairus socius nests to Kalahari animal and plant communities. The objectives are to investigate the diversity of animals associated with the nests, the interactions between these species, and to gain insights into the life histories of associated species. We also aim to understand how the ‘ecological engineer’ potential of these nests may have community-wide impacts on structure and function, and how this impact may change across environmental gradients.
Evidence of the importance of facilitation in communities has accumulated, which challenges traditional emphasis of negative interactions in ecology. In particular, facilitative interactions are predicted to increase in importance in stressful environments and may become a crucial component of the adaptive responses of communities under stress. Ecological engineers – species that modify habitats and ameliorate abiotic stress for other species – are a key research focus. Identifying and understanding the impact of ecological engineers is vital, especially in arid environments that are expected to become harsher with global climate change.
Pygmy Falcons Polihierax semitorquatus are the most controversial user of the weaver colonies. They never construct their own nests, depending entirely on weaver colonies, which is a unique obligate nesting association. Pygmy Falcons also, albeit rarely, prey on weaver nestlings and even adults, suggesting a semi-parasitic relationship between the species. We aim to describe the natural history and ecology of Pygmy Falcons, and to characterize their interactions with Sociable Weavers; do falcons provide benefits to weavers or are they vertebrate parasites?
Sociable Weavers forage on plants and insects across the landscape and bring material back to their nest trees in the form of faeces, feathers and carcasses. This nutrient input at weaver nests results in these sites being islands of fertility in the landscape. We study how this alters the soil chemistry, as well as soil nematode and plant communities.
Activities in 2020
- Despite the COVID-19 challenges, PhD students Olufemi Olubodun and Timothy Aikins Khan completed their field seasons. Timothy is investigating the costs and benefits to Camelthorn Vachellia erioloba and Shepherd’s Boscia albitrunca trees from hosting Sociable Weaver nests and collected most of the field data for soil and plant analyses. Olufemi is investigating various aspects of the life history of Pygmy Falcons and monitored the breeding success and group composition of the falcon population.
- This was the 10th field season at Tswalu Kalahari Reserve. Good summer rains finally fell on the study site resulting in an excellent Sociable Weaver and Pygmy Falcon breeding season. The boom year saw us ringing 65 fledging falcon chicks to date, despite the frequent presence of Boomslangs and Cape Cobras at nests, with second falcon broods still to be ringed.
- Olufemi and Anthony Lowney obtained the first detailed GPS tracking data from Pygmy Falcon pairs, to investigate territoriality and the workload of helpers.
- Data collection towards the Kalahari Endangered Ecosystem Project (KEEP), a collaboration with WITS, UP, UNISA and UWC researchers, continued. These long-term data will contribute to identifying the impacts of climate change on the Kalahari ecosystem.
- Timothy and Olufemi presented talks highlighting their initial results at the Department of Biological Sciences research day.
- Anthony Lowney was awarded his PhD for his thesis “Sociable weaver nests as a resource to local animal communities”. Anthony is the first PhD student to graduate from this project. He first helped on the project in 2013 and 2014, before starting his thesis in late 2015.
- 2020 was a productive year, with four articles published in international journals:
- Lowney et al. in Behavioral Ecology showed how Kalahari Tree Skinks Trachylepis spilogaster eavesdrop on Sociable Weavers to manage predation by Pygmy Falcons and expand their realised niche.
- Jess Lund’s Honours project investigating winter thermoregulation in free-ranging Pygmy Falcons in the Kalahari Desert was published in the Journal of Ornithology.
- Honours projects by Kervin Prayag and Carla du Toit were combined into a paper in Ecology and Evolution on faunal input at host plants, showing how Camelthorn Trees use nutrients imported by Sociable Weavers.
- Lowney et al. in Frontiers in Ecology and Evolution used temperature data-loggers to show that the large communal nests of Sociable Weavers provide a year-round insulated refuge for weavers and Pygmy Falcons.
- Timothy Aikins Khan and others contributed a FitzNews piece in African Birdlife magazine highlighting the potential costs and benefits of Sociable Weaver nests to their host’s trees.
Impact of the project
This project is providing unique insights into the community ecology and between-species interactions in the Kalahari. It will quantify the ecological engineering role of the Sociable Weaver and potentially determine the role of Sociable Weaver nests in a warming and increasingly arid Kalahari. The outputs of this project will also contribute to available eco-tourism information that enhances the experience of visitors to landscapes within the distribution of the Sociable Weaver.
Key co-supportersDSI-NRF CoE grant; Tswalu Foundation; University of Cape Town launching grant, Suzuki South Africa.
Research team 2020
Dr Robert Thomson (FIAO, UCT)
Dr Diana Bolopo (FIAO, UCT)
Prof. Michael Cramer (Biological Sciences, UCT)
Prof. Andrew McKechnie (U. Pretoria)
Dr Mariette Marais (ARC – Plant Protection Research Institute, Pretoria)
Dr Bryan Maritz (UWC)
KEEP team (led by Prof. Andrea Fuller, and Prof Graham Alexander, both WITS)
Students: Timothy Aikins Khan (PhD, UCT); Anthony Lowney (PhD, UCT); Olufemi Olubodun (PhD, UCT).