Sociable Weaver nests as a resource
This project examines the importance of Sociable Weaver Philetarius 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?
Activities in 2017
- BTech student Bonginkosi Ngomane (Tshwane University of Technology) investigated the impact of Sociable Weaver nests on plant community and diversity structure below colony trees.
- PhD student Anthony Lowney experimentally tested the interspecific hierarchy of the avian community that uses weaver chambers for roosting. Initial findings show that the hierarchy stands as (most dominant first) Pygmy Falcon, Acacia Pied Barbet Tricholaema leucomelas, Sociable Weaver, Ashy Tit Parus cinerascens and Scaly-feathered Finch Sporopipes squamifrons.
- Using playback experiments and presenting snake stimuli, Anthony also tested whether the Pygmy Falcons provide protection benefits to Sociable Weavers. Results suggest that Pygmy Falcons may provide colony defence, but only while they are breeding.
- UCT Hons student Billi Krochuk investigated the function of the conspicuous white faecal mat at the entrance of the colony chambers used by the Pygmy Falcons. She tested whether this mat has any antimicrobial function, thermal buffering effect or social signalling purpose for the Sociable Weavers.
- The Pygmy Falcon population in the study area was monitored for the seventh season. Postdoctoral Fellow Diana Bolopo has used these data to study the breeding ecology of the Pygmy Falcons. They present an unusual breeding strategy in birds: cooperative breeding, in which more than two adults attend a nest to fledge the chicks.
- A note describing intraspecific killing by a Pygmy Falcon was published in the Journal of Raptor Research.
- A note on the use of Sociable Weaver colonies by Cheetahs was published in Biodiversity Observations.
- Diana Bolopo presented the results of the breeding ecology of the Pygmy Falcons in an oral communication at the European Ornithological Union conference, held in Turku, Finland.
- Honours student Billi Krochuk, PhD student Anthony Lowney, and Robert Thomson all presented at the 8th Diamond Route Research Conference in Johannesburg.
Impact of the project
This project will provide 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.
DST-NRF CoE grant; Tswalu Foundation; Academy of Finland; University of Cape Town launching grant.
Dr Robert Thomson (FIAO, UCT)
Dr Diana Bolopo (FIAO, UCT)
Assoc. Prof. Michael Cramer (UCT)
Dr Bryan Maritz (UWC)
Students: Anthony Lowney (PhD, UCT); Billi Krochuk (BSc Hons, UCT); Bonginkosi Prince Ngomane (BTech, TUT).