Cooperation and population dynamics in the Sociable Weaver | FitzPatrick Institute of African Ornithology

Our long-term project at Benfontein Reserve uses the fascinating Sociable Weavers Philetairus socius to study questions about the ecology and evolution of social behaviour. We investigate whether sociality contributes to buffer against the extremes of the Kalahari climate and focus on whether individuals that are more cooperative are preferred as partners. The extreme weather experienced in recent years and destructive fires provided an unsolicited but interesting opportunity for research.

The Sociable Weaver population at Benfontein seems to be getting some respite after a series of adverse events – two fires, weather extremes and what seems to have been an outbreak of avian pox at one of the colonies – decreased the population to its lowest in 31 years of records. These adversities however demonstrate the importance of long-term studies. The long-term data that have been collected by Rita Covas and Claire Doutrelant, allowed us to describe some of the key demographic, genetic and social changes associated with natural catastrophes. For example, we found that the most destructive fire led to a rearrangement of the colonies’ social structure, with the levels of genetic relatedness decreasing within colonies and, strikingly, the species’ characteristic family-based breeding groups giving way to groups composed of immigrants and family members. Post-doctoral fellow Sophie Dupont is investigating how the stress arising from the fire influenced telomere attrition and survival. In an impressive effort, Sophie extracted over 900 DNA samples, which will be used to understand how catastrophic events affect physiology and their long-term consequences.

It’s not only the weavers that show resilience in the face of disaster. PhD student Babette Fourie spent several weeks rebuilding the sophisticated automatic feeders that were destroyed by the 2023 fire. This ambitious experiment aimed to manipulate familiarity at the feeders and foster new social associations among the birds. The experiment was finally conducted at the end of 2024 and the preliminary results show that sociable weavers can form new ‘friendships’ when forced to interact with birds outside of their usual social group. Forming friendships is important, Post-doctoral fellow Gabriel Munar’s results showed that birds with a higher number of strong social associations have higher survival. Gabriel’s work is part of a European Research Commission (ERC) funded study looking at the bases of partner choice in animal societies. To achieve these goals, Liliana Silva is developing AI-based models for behavioural identification.

PhD student Marta Marmelo continued her study of whether cooperation is a repetitive trait, and whether some individuals are consistently more cooperative than others. Marta started by studying mobbing in Sociable Weavers by presenting models of snakes and Pygmy Falcons Polihierax semitorquatus. Work on another cooperative behaviour, nest building, was conducted by PhD student Nicolas Silva. Nicolas found that male sociable weavers, and especially older males, build slightly more than females, and prefer to build with larger straws. Nicolas also studied social dominance and associated signalling and sexual selection in this species. He found that, in spite of sociable weavers’ dull plumage and lack of sexual dimorphism, there is evidence for sexual selection in this species, in both sexes, which is an original finding. New post-doctoral fellow Jorge Garcia Campa, will investigate whether females prefer to mate with more cooperative males.

Activities in 2024

Two new post-doctoral fellows joined the project – Gabriel Munar will investigate fitness benefits of social bonds and Jorge Campa will investigate whether more cooperative individuals are preferred as sexual partners.
Sophie Dupont extracted >900 DNA samples in the lab.
Babette Fourie ran a fascinating experiment to manipulate feeding behaviour and social associations. The experimental apparatus is a sophisticated system based on RFID technology which was entirely built by Babette.
Marta Marmelo is investigating the reliability of helping behaviour and initiated a study of mobbing behaviour in Sociable Weavers.
Liliana Silva set up an AI-assisted pipeline for video analyses that can automatically describe the behaviours taking place at the nest. A manuscript on this was submitted to a special issue of Methods in Ecology and Evolution on Deep Learning.

Highlights

New funding from the Marie Curie Staff Exchange, EU, was granted to a consortium of researchers from CIBIO-Univ Porto, the French National Centre for Scientific Research (CNRS), the University of Zurich and the Fitz to continue our work on developing AI-based methods for the automatic identification of individual and behavioural features.
Nicolas Silva successfully defended his PhD at the University of Montpellier in December.
Pietro D’Amelio and colleagues published two papers, one in the American Naturalist on the benefits of monogamy, and the other in a special issue of Ostrich, in memory of Richard Dean, describing the highly original and flexible breeding phenology of sociable weavers.
Rita Fortuna published the last chapter of her PhD thesis in Behavioural Ecology, detailing how a perceived predation threat might influence maternal investment.
Rita Covas and others published a paper in Evolution showing that family-living and cooperative breeding in birds are associated with the number of avian predators

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 provide insight into whether and how sociality mediates the response to a changing environment.

Key co-supporters
European Research Council (ERC); Marie Curie – Staff Exchange (EU); French Research Agency (ANR); Portuguese Foundation for Science and Technology.

Research team 2024
Team leaders and collaborators:
Dr Rita Covas (FIAO, UCT and CIBIO, U. Porto)
Dr Claire Doutrelant (FIAO, UCT and CNRS, France)
Dr Fanny Rybak (U. Paris-Sud, France)
Liliana Silva (CIBIO, U. Porto)
Dr André Ferreira (U. Zurich, Switzerland))
Dr Sophie Dupont (U. Montpellier, CNRS, France))
Dr Jorge Campa (CIBIO, U. Porto))
Dr Gabriel Munar (CIBIO, U. Porto))
Franck Théron (CIBIO, U. Porto)

Students:
Babette Fourie (PhD, U. Porto); Marta Marmelo (PhD, U. Porto); Nicolas Silva (PhD, U. Montpellier).

Research Assistants:
Lesedi Moagi, Justin Jacobs, Owami Mashaba, Yoann Depalle, Natacha Ampe, Paulo Ditzel, Marine Hoareau, Hippolyte Dupas.

After setting up several video cameras, PhD student Marta Marmelo hides a fake snake which she will use to study mobbing behaviour in sociable weavers. Marta is hoping to determine whether some individuals have a higher propensity to mob predators than others. She is also hoping to uncover whether sociable weaver emit different alarm calls when threatened by ground or aerial nest predators (snakes or pygmy falcons in this study) (Photo: Jorge Campa).

Sociable Weavers build and maintain their nests communally throughout the year, but who builds, where and when, and - more interestingly - why, remains an elusive question. We are now recording nest building behaviour throughout the year to address these questions (Photo: Maxime Loubon).

Two Sociable Weavers feed at one of the project's feeding stations. These stations are equipped with RFID antennas that record the PIT-tags carried by the birds on a leg ring. The data obtained allows us to study social associations in this species and answer questions such as whether birds that cooperate more have a better social position in the colony (Photo: Cecile van Steenberg).

A devastating fire at Benfontein reserve in September 2021 burned down most of the Sociable Weaver colonies in our long-term study area. Franck Théron, who has worked on the project since 2013, stands next to a scorched Vachellia erioloba that used to house 45 pairs of Sociable Weavers (Photo: Tanguy Deville).