This project examines the importance of Sociable Weaver Philetairus socius and other weaver nests to Kalahari animal and plant communities. The objectives are to investigate the diversity of animals associated with weaver 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, challenging the traditional emphasis on negative species 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 due to global change. 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 due to global climate change.

Pygmy Falcons Polihierax semitorquatus are the most “controversial” users of Sociable Weaver colonies. They never construct their own nests and depend entirely on weaver colonies, which is a unique obligate nesting association. Pygmy Falcons also prey on weaver nestlings and even adults, suggesting a semi-parasitic relationship between the species. We explore the interactions between weaver hosts and falcons, to determine whether the falcons provide benefits or costs to the weavers. Furthermore, we study the natural history and ecology of the Pygmy Falcon, and the long-term population demographic responses of the falcon to weather and environmental change.

As colonial breeders, Sociable Weavers bring material back to their nest trees in the form of faeces, feathers, and carcasses. This nutrient input results in weaver nests being islands of fertility in the landscape. We study how this alters the soil chemistry, as well as soil nematode and plant communities. We further investigate the effect of this fertile island on host tree seedlings, host tree productivity and the potential costs of supporting such a huge nest .

Activities in 2024

  • PhD student Olufemi Olubodun started the year off in January hosting a film crew from NHK (Japanese national television) on Tswalu Kalahari. The crew shot a program for their Darwin’s Amazing Animals series that explores the ecosystem engineering role of the Sociable Weaver and activity of other animals at their nest colonies. The documentary aired in May 2024.
  • CB MSc student Lesedi Moagi worked on weaver nests as a resource on Tswalu Kalahari using White-browed Sparrow-Weaver nests as her study system as they are more amenable to conducting field experiments. Lesedi explored the role of old weaver nests in the Kalahari as an important part of habitat, investigating effects on the local resident bird community.
  • MSc student Sthabile Khumalo returned to the field to collect samples for her study exploring the physiological stress responses of Sociable Weavers when hosting Pygmy Falcons in their colonies. The 14th season of detailed monitoring of Sociable Weaver colonies and the individually marked Pygmy Falcon population at Tswalu Kalahari was completed.
  • After the near-complete breeding failure of Pygmy Falcons in 2023, the 2024 breeding season featured at least 28 active nests. In total, 14 new Pygmy Falcon adults were colour-ringed, and 20 fledging chicks (many nests remain active in January 2025). At least 25 other colour ringed adult falcons were retrapped or resighted.

Highlights:

  • The project hosted the Conservation Biology MSc field camp again in 2024. The class were able to witness the magnitude of the Sociable Weaver nest and think about their role in the Kalahari ecosystem. They also contributed to the capture of an unringed pair of pygmy falcons for colour-ringing.
  • The project inspired artist Karen Stander who made several art pieces representing the weaver nests and their role and representation of resilience in the harsh Kalahari. The exhibition was entitled “Hotel Kalahari”

Impact of the project

This project provides unique insights into the community ecology and between-species interactions in the Kalahari. It highlights fascinating natural history stories and brings attention to this unique system. We quantify the ecological engineering role of the Sociable Weaver and determine the potential role of Sociable Weaver nests in a warming and increasingly arid Kalahari. The outputs of this project also contribute to eco-tourism information to enhance the experience of visitors to landscapes within the distribution of the Sociable Weaver.

Key co-supporters

Tswalu Foundation, DECRA -Australian Research Centre.

Research team 2024
Team leaders and collaborators:
A/Prof. Robert Thomson (FIAO, UCT)
Dr Celiwe Ngcamphalala (Biological Sciences, UCT)
Dr Anthony Lowney (U. Hartpury / FIAO, UCT)
Prof. Michael Cramer (Biological Sciences, UCT)
Dr Ben Ashton (U Flinders / FIAO, UCT)
Dr Inês Gonçalves (U. Bristol)

Students:
Olufemi Olubodun (PhD, UCT), Sthabile Khumalo (MSc, UCT), Lesedi Moagi (CB MSc, UCT)