This project examines the importance of Sociable Weaver Philetairus socius and White-browed Sparrow-Weaver Plocepasser mahali nests to Kalahari animal and plant communities. The objectives are to investigate the diversity of animals associated with weaver nests and the interactions between these species, and to gain insights into the life histories of associated species. The project also has a particular focus on the Pygmy Falcon Polihierax semitorquatus and aims to understand how its presence potentially impacts Sociable Weavers as ‘ecological engineers’.

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.

The project has long focused on the ecological facilitation and impacts of Sociable Weaver nests, and while this work continues as long-term data collection, experimental possibilities for manipulating the resource are limited. A switch to using White-browed Sparrow-Weaver nests in experimental protocols now enhances our ability to conduct large-scale field experiments with nests to test their impacts on animal and plant communities. This system permits more detailed exploration of the role of nest density, nest spatial distribution, nest quality and other factors in their ecological impacts, particularly on the avian community.

Pygmy Falcons are the most ‘controversial’ user 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 the level of stress incurred by the weavers in the presence of the falcons. 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.
 

Activities in 2025
  • After submitting her thesis, Conservation Biology MSc student Lesedi Moagi returned to the field to collect additional data on the long-term effects of the experimental nest structures on the Kalahari avian communities. The new data has been incorporated into her MSc results and a manuscript is being prepared for publication.
  • MSc student Sithabile Khumalo presented her research findings at the Zoological Society of Southern Africa conference in Rawsonville. The presentation was titled ‘Stress responses of Sociable Weavers to the presence of Pygmy Falcons.’
  • Lesedi presented at the 14th Oppenheimer Research conference in
    Johannesburg on her experimental findings, which showed that avian diversity and abundance increased after Sparrow-Weaver nest structures were added in areas where they were previously absent.
  • A/Prof. Robert Thomson presented the latest unpublished work on Pygmy Falcon movements and home range size at the 2025 Raptor Research Foundation Conference, San Jose, Costa Rica.
  • The Pygmy Falcon genome was sequenced through an application to the 1KSA project ‘Decoding South Africa’s Biodiversity’. In addition, DNA extraction for short-read sequencing from 30 existing blood samples was performed. From these data, variable positions in the genome (microsatellites and single nuclear polymorphisms) will be identified, and these will later be used to study the genetics of the mating system of the Pygmy Falcon.
  • 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”.
Highlights
  • PhD student Olufemi Olubodun submitted his PhD thesis entitled ‘Life history and population dynamics of the African Pygmy Falcons – an obligate associate of the Sociable Weaver’. The thesis was passed and Olufemi will graduate in early 2026. He also presented an overview of his PhD findings at the 2025 FitzPatrick Annual General Meeting.
  • Lesedi Moagi graduated during the Spring 2025 graduation period and was awarded a UCT URC scholarship to conduct her PhD on this project, continuing her exploration of questions about weavers as ecosystem engineers in the Kalahari. Lesedi will begin her PhD research in 2026.
  • Lesedi’s MSc research findings were featured in the Oppenheimer Generations Research and Conservation newsletter and Mail & Guardian.
  • The project again hosted the Conservation Biology MSc field camp. The class were able to witness the magnitude of the Sociable Weaver nest colonies and think about their role in the Kalahari ecosystem. In addition, the data from the 2024 field camp project,
    which focused on the herbivory of mistletoe, formed part of a 2025 publication 2025 entitled ‘Mistletoes as indicators of the intensity of browsing by large mammals in Kalahari Savanna’ published in the African Journal of Ecology.
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, UCT BRAAS grant, DECRA – Australian Research Centre.

Research team 2025
Team leaders and collaborators:
A/Prof. Robert Thomson (FIAO, UCT)
Dr Celiwe Ngcamphalala (Biological Sciences, UCT)
A/Prof. Robert Ingle (MCB, UCT)
Prof. Michael Cramer (Biological Sciences, UCT)
Dr Ben Ashton (U Flinders / FIAO, UCT)
Dr Inês Gonçalves (U. Bristol)
Dr Anthony Lowney (U. Hartpury / FIAO, UCT)

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