The elaborate social system and cooperative behaviour of Sociable Weavers Philetairus socius make this Kalahari endemic bird an ideal species to study cooperation. Our long-term project at Benfontein Reserve focuses on cooperative breeding, nest-building and vigilance against predators to understand the fitness benefits and costs of cooperating. Our long-term data also provide insights into how social and environmental variation influence reproduction and survival, and how this ultimately influences population trends. A recent fire at the study site in 2021 inadvertently led to a new line of research on the social and demographic effects of natural catastrophes.

The Sociable Weaver population at Benfontein is slowly recovering from the destructive fire that burned down nine of the 15 colonies in this long-term study led by Rita Covas and Claire Doutrelant. Colony captures in September 2022 revealed that the colonies that survived in the area received many immigrants from the colonies that were destroyed. This means that the population now comprises ca. 60% of the birds studied before, even though only 40% of the colonies survived. There was also a short but significant breeding activity that produced a total of 142 fledglings (although this is a low number for sociable weavers given the low post-fledging survival).

New MSc student, Mariana Sousa, is using video data and observations that had been collected immediately before and after the fire, together with additional data collected at the end of 2022, to quantify the increased levels of aggression associated with the sudden increase in colony size, and whether pre-fire social bonds were associated with increased probability of successfully settling at one of the surviving colonies. Additional work will continue to monitor how the disruption affected post-fire social associations, reproduction, long-term physio-logical damage and survival, among other questions. Thus the fire led to a sad but highly relevant new line of investigation, as natural catastrophes are increasing under ongoing climate change.

In spite of the commotion caused by the fire, other activities started again or were concluded. Rita Fortuna successfully defended her PhD thesis on maternal effects in May and Marta Marmelo obtained her MSc degree by describing vigilance behaviour in sociable weavers. Significant progress was made by Liliana Silva and Nicolas Silva in developing methods of artificial intelligence to automatically analyse behaviour and phenotypic traits from images collected in the field, and Pietro D’Amelio (in collaboration with the Max Planck Institute) successfully developed a system to record individual vocalisations from free ranging individuals in the field, opening the door to exciting new research possibilities. New PhD student, Babette Fourie, started work towards understanding social associations in the sociable weavers, and developed an impressive automatic feeder that uses RFID technology to target specific individuals and manipulate access to food, allowing us to artificially create ‘pro-social’ individuals (that provide others with access to food) and ‘selfish’ ones (that only feed themselves). These projects are part of larger projects into the study of nests as extended phenotypes (French ANR funding) and into the role of partner choice on the evolution and stability of cooperation (European Research Commission grant).

Activities in 2022

  • The project’s fieldwork is now running continuously throughout the year, collecting data on nest building behaviour and on social associations (feeding and roosting) during the non-breeding season. This will lead to a better understanding of social structure and benefits of group membership.
  • Detailed data on nest building, which forms part of Nicolas Silva’s PhD, is allowing the quantification of possible benefits and costs for the individuals involved.
  • Advances in video analysis led by Liliana Silva, André Ferreira and Nicolas Silva are now allowing us to conduct semi-automatic analyses of nest provisioning data and vigilance, and extraction of phenotypic data (e.g. plumage patch size) from videos and photos collected in the field. Work is continuing to improve these methods (currently at >70% accuracy). 
  • Pietro D’Amelio successfully implemented a method that uses miniature on-board microphones to record individual vocalisations in cooperative groups. 

Highlights

  • Rita Fortuna concluded her PhD investigating maternal allocation in relation to weather, predation and social factors.
  • The sociable weaver team presented six talks at the conference of the International Society for Behavioural Ecology in Stockholm, Sweden (July-Aug). The topics covered methodological developments using Artificial Intelligence to automatically collect data from images, on-board microphones to record individual vocalisation, an experiment about the effects of predation on maternal investment and a description of infanticide in sociable weavers.
  • A study that used oxidative stress to assess the physiological costs of helping, and how that influences helping decisions, was published in Behavioral Ecology.
  • A study investigating begging behaviour and feeding responses from parents and helpers was published in Animal Behaviour.

Impact of the project
The long-term nature of this project allows unique insights into the evolution of cooperation and the mechanisms that allow it to persist. The demographic data allow for examination of the factors affecting population dynamics, provide a baseline against which to study environmental change and natural disasters, which are increasing in frequency under climate change, and inform us on whether and how sociality mediates the response to a changing environment.

Key co-supporters
European Research Council (ERC); French Research Agency (ANR); DSI-NRF CoE grant; Portuguese Foundation for Science and Technology (FCT); Marie Curie Fellowships (EU).

Research team 2022
Dr Rita Covas (FIAO, UCT and CIBIO, U. Porto)
Dr Claire Doutrelant (FIAO, UCT and CNRS, France)
Dr Fanny Rybak (U. Paris-Sud, France)
Dr Pietro D’Amelio (CNRS, France)
Liliana Silva (CIBIO, U. Porto)
Dr André Ferreira (U. Zurich, Switzerland)

Students:  Rita Fortuna (PhD, Porto); Babette Fourie (PhD, Porto and Montpellier); Marta Marmelo (MSc, Porto), Nicolas Silva (PhD, Montpellier); ), Fantine Benoît (MSc, Montpellier); Mariana Sousa (MSc, Porto).

Research Assistants: Franck Théron, Tanguy Deville, Angelique Lazarus, Tshianeo Ndou, Natasha Prindal, Lesedi Moagi, Carlotta Bonaldi, Paola Stefanini, Shiara Covenden.