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.
Activities in 2016
- PhD student Anthony Lowney quantified the diversity of animals using Sociable Weaver nests at monthly intervals throughout 2016. Camera traps showed frequent use by mammals for shade (Kudu Tragelaphus strepsiceros, Impala Aepyceros melampus), foraging (Chacma Baboon Papio ursinus, Slender Mongoose Galerella sanguinea), refuge (Leopard Panthera pardus, African Wild Cat Felis silvestris), and as a vantage point (Cheetah Acinonyx jubatus). Night visits revealed that 87% of nests host multiple species, such as African Pygmy Falcons Polihierax semitorqutus, Acacia Pied Barbets Tricholaema leucomelas, Ashy Tits Parus cinerascens and Scaly-feathered Finches Sporopipes squamifrons. Furthermore, the number of species and their abundance changes across the year.
- Anthony also counted Kalahari Tree Skinks Trachylepis spilogaster and assessed their behaviour in contexts when Sociable Weavers were present at nest colonies and when they were not. This investigation will continue with an experimental test in 2017.
- The African Pygmy Falcon population breeding in the study area was monitored for the sixth season. In 2016, all individuals received colour rings to facilitate with the long-term demographic study of this species.
- Led by Post-doc Diana Bolopo, GPS loggers were sourced for attachment to African Pygmy Falcons. These devices will be used to study territoriality of this species in addition to habitat use and dispersal of individuals.
- UCT BSc Hons students Kervin Prayag and Carla du Toit investigated the impacts of Sociable Weaver nests on landscape soil nutrient concentrations and the impacts on the host Camelthorn Vachellia erilooba trees. They found that the soils below Sociable Weaver nests had highly enriched soil nutrient concentrations due to the accumulated faecal droppings. These nutrients were used by the trees, and trees with Sociable Weaver nests had 27% more leaves per branch than trees without nests. But the costs of hosting weaver
- nests were also measured in terms of a reduced canopy volume and increased likelihood of branch fall and lost biomass.
- Diana Bolopo joined the project as a Post-doc and subsequently received a Claude Leon Postdoctoral Fellowship to continue her work on this project.
- BSc Hons students Kervin Prayag and Carla du Toit presented their findings at the Arid Zone Ecology Forum meeting and the Diamond Route Conference respectively, and both are currently preparing a manuscript for submission in early 2017.
- Robert Thomson presented a talk on Sociable Weaver nests as a resource to Kalahari animals at the Pan-African Ornithological conference in Dakar, Senegal.
- A collaboration was initiated with Bryan Maritz (UWC), a herpetologist, to study the importance of Sociable Weaver nests to Cape Cobras and Boomslangs. The collaboration will also investigate the interactions of snakes with other nest associates.
- The project activities were filmed twice by the BBC. The first piece featured Anthony Lowney working with African Pygmy Falcons, and was aired on BBC’s “Naomi’s Nightmares of Nature” in 2016. The second film crew came in December 2016 specifically to film falcon-weaver interactions at nests for a new series called “Animals Behaving Badly” that will be aired in 2017.
- Anthony Lowney’s paper about territorial fights among Pygmy Falcons was accepted by Journal of Raptor Research.
- Anthony published a short note about the Cheetah’s use of Sociable Weaver nests as look-out points in Biodiversity Observations.
Impact of the project
This project will provide unique insights about the community ecology and between-species interactions in the Kalahari. It will also explore the potential ecological engineering role of the Sociable Weaver, as well as contribute to available eco-tourism information that enhances the experience of visitors to landscapes within the distribution of the Sociable Weaver.
Academy of Finland; University of Cape Town launching grant; DST-NRF CoE grant; Tswalu Foundation.
Dr Robert Thomson (FIAO, UCT)
Dr Diana Bolopo (FIAO, UCT)
Associate Prof. Michael Cramer (UCT)
Dr Dieter Oschadleus (ADU, UCT)
Dr Bryan Maritz (UWC)
Students: Anthony Lowney (PhD, UCT); Carla du Toit (BSc Hons, UCT); Kervin Prayag (BSc Hons, UCT)