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Cooperation and population dynamics in the Sociable Weaver

The elaborate social system and cooperative behaviour of Sociable Weavers Philetairus socius make this Kalahari endemic bird an ideal species to study the costs and benefits of cooperation. This long-term project started by focusing on cooperative breeding but is now starting to focus on other cooperative behaviours, such as nest building and vigilance against predators. In addition, the long-term data gathered is used to obtain a better understanding of how environmental changes influence basic demographic parameters, such as reproductive output and survival, and how this may ultimately influence population trends.

Understanding how cooperation evolved and is maintained is a challenging question in evolutionary biology because natural selection is thought to favour selfish individuals over co-operators. However, cooperation is widespread in nature. One of the key evolutionary forces favouring cooperative behaviour is thought to be kin selection, where individuals help close kin. However, theory and studies in humans also suggest that co-operators are preferred as social and sexual partners. Partner choice may therefore provide an additional explanation for the evolution and stability of cooperation, but we lack an understanding of its importance in natural systems. This is now an important focus of the Sociable Weaver project, led by Rita Covas and Claire Doutrelant.

Recent grants from the European Research Council (ERC) and French Research Agency (ANR) will allow us to focus on this topic over the next five years. With this sustained funding, we will also be able to continue our long-term research into how environmental changes influence population dynamics, and whether and how sociality may buffer against the negative effects of adverse conditions, such as heatwaves or prolonged droughts which are expected to increase under the current global climate crisis.

Activities in 2020

  • The COVID-19 pandemic had an important impact on our field activities and overall productivity. Most field team members had to leave the study area before the end of March, when the Sociable Weavers were still breeding. We were fortunate to have the help of previous field manager Michelle Schroeder, who was able to continue the basic monitoring of reproduction until the end of the breeding season in June. However, some long-term behavioural data could not be collected.
  • With the travel restrictions still in place, we were not able to conduct our annual captures of the study population at the end of winter (before the start of the breeding season), which has consequences for data continuity. We also had to postpone all the experiments and additional data collection that was planned for the 2020/21 breeding season.
  • Field work resumed at the end of September with a small team from South Africa and Lesotho. Two new students joined the project: MSc student Lucas Pacheco (CIBIO, University of Porto, Portugal) started a project on roosting association, and PhD student Nicolas Silva (CNRS and U. Montpellier, France) is working on cooperative nest building behaviour.
  • In spite of the travel restrictions, data analyses and writing up of manuscripts continued and four manuscripts were produced. These focused on methodological developments, maternal effects and potential physiological benefits of having helpers at the nest. All team members were also involved in online conferences and seminars, remaining engaged with the international research community. We continued to have weekly meetings (which became fully online), where all group members shared their work progress. These meetings provided opportunities to discuss problems or questions in spite of lockdown or travel restrictions.

Highlights

  • Two new grants started during 2020: Rita Covas received an ERC grant from the European Union to study the role of partner choice on the evolution of cooperation and Claire Doutrelant received a French National Research Agency grant to study the role of sexual and social selection in the evolution of nest building in Sociable Weavers.
  • Post-doc Pietro D’Amelio was awarded a Marie Curie fellowship to work on the role of social behaviour in mate choice.
  • André Ferreira (CNRS, U. Montpellier) led a paper published in Methods in Ecology and Evolution describing a new method that uses artificial intelligence to identify small birds based on individual feather patterns. This study has received a great deal of attention from the international media (e.g. articles in Science, The Guardian, New Scientist and many others).
  • Another paper with André as the leading author focused on the collection of social association data and was published in Ecology and Evolution.
  • Rita Fortuna (CIBIO, U. Porto) had her first PhD paper accepted in the Journal of Animal Ecology. Her paper used long-term data to investigate maternal allocation in relation to weather, predation and social factors in Sociable Weavers. Rita also presented this work at the online Long-Term Animal Research Seminar Series hosted by Duke University, USA.

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 in relation to environmental change.

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

Research team 2020
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 (FIAO)
Dr Julien Renoult (CEFE-CNRS, France)
Dr Damien Farine (Max Planck Institute, Germany)

Students: André Ferreira (PhD, Montpellier); Rita Fortuna (PhD, Porto); Martin Quque (PhD, Strasbourg); Nicolas Silva (PhD, Montpellier); Lucas Pacheco (MSc, Porto).

Research assistants: Franck Théron, Liliana Silva, Corisande Abiven, Louis Bliard, Annie Basson, Michelle Schroeder, Shobana Makhubu, Richard Wilks, Bronwyn Dunlop, Stuart Dunlop.