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 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 project, led by Rita Covas and Claire Doutrelant, suffered a major blow at the end of September 2021 when a devastating fire destroyed many of the long-term study colonies. The unusual fire burned for days, fuelled by large volumes of dry biomass resulting from exceptional rains the previous summer. Despite the best efforts of the field team to fight the fire, most Sociable Weaver colonies at Benfontein burned. Fortunately, eight colonies survived to continue our study of cooperation and population dynamics.

Thanks to the impressive commitment of the field team, we were able to document in detail the effects of the fire on the numbers of birds in each colony. We observed a sudden marked increase in size of the surviving colonies associated with increased levels of aggression, and we continue to monitor how the disruption affected colony composition, reproduction, etc. This opens a sad but interesting line of investigation as natural catastrophes are increasing under ongoing climate change.

In spite of the fire, 2021 was a good year for the Sociable Weaver project. Two studies were published, one led by Rita Fortuna and one by Pietro D’Amelio showing how weather, nest predators and social factors interact to determine maternal investment and reproductive output, respectively. André Ferreira concluded his PhD thesis on social preferences, kinship and helping behaviour, and three new MSc projects by Lucas Pacheco, Marta Marmelo and Benjamin Dupuis started to provide insights into roosting associations, vigilance behaviour and the demographic effects of predator exclusion. These projects are part of the first steps that we are taking towards the objectives of our European Research Commission (ERC) grant on understanding the role of partner choice for the evolution and stability of cooperation.

Activities in 2021

The 2020/21 breeding season was unusually short, ending in mid-February, probably due to very high rainfall in the early summer. This led to unusually lush grass growth, which appears to have been too much for the semi-desert Sociable Weavers.
After the pandemic-imposed break, annual captures of all birds in our colonies resumed with a total of 520 birds caught and ringed.
Thanks to European and French grants, we conducted fieldwork throughout the year for the first time, collecting data on nest building behaviour and on feeding and roosting associations, which 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.
2021 was a year of intensive data analysis and manuscript preparation, as André Ferreira and Rita Fortuna approached the end of their PhDs, and Pietro D’Amelio concluded analyses on our long-term data. Four manuscripts were published or accepted for publication.
Advances in video analysis led by Liliana Silva (CIBIO, U. Porto) now allows provisioning data to be analysed semi-automatically, and trials of fully automated analyses are promising, currently at >70% accuracy.
Pietro D’Amelio started trials with miniature on-board microphones with the aim of recording individual vocalisations in cooperative groups.

Highlights:

André Ferreira concluded his PhD entitled Social preferences, kinship and helping behaviour in a colonial cooperatively breeding bird with an outstanding defence.
Rita Fortuna published a paper in the Journal of Animal Ecology using our long-term data to investigate maternal allocation in relation to weather, predation and social factors. Rita had another paper accepted in Behavioral Ecology on begging behaviour and the feeding responses of parents and helpers.
Pietro D’Amelio further demonstrated the value of long-term and experimental data with a publication in Ecology Letters reporting climatic and nest-predation effects on reproductive output. The study revealed that hot, dry weather was a major driver of nestling mortality, and that the presence of helpers at the nest, although positive, did not mitigate the effects of adverse weather. It seems that cooperative breeding might have a limited capacity to mitigate extreme weather effects.
A study that used oxidative stress to assess the physiological costs of helping, and how that influences helping decisions, was accepted for publication in Behavioral Ecology.

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 and provide a baseline against which to study the extreme environmental events that increased in frequency under climate change.

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 2021
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)

Students: André Ferreira (PhD, Montpellier); Rita Fortuna (PhD, Porto); Nicolas Silva (PhD, Montpellier); Benjamin Dupuis (MSc, Montpellier); Lucas Pacheco, (MSc, Porto); Marta Marmelo (MSc, Porto).

Research Assistants: Franck Théron, Liliana Silva, Annie Basson, Tanguy Deville, Bronwyn Dunlop, Stuart Dunlop, Andrew Elliot, Angelique Lazarus, Tshianeo Ndou, Natasha Prindal, Deborah Walsh.

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).

The Sociable Weaver project monitors each breeding attempt in detail and nests are recorded to identify all the individuals assisting to raise the young (Photo: Alexandre Vaz).

A new technique based on artificial intelligence now allows us to identify individual birds based on the unique pattern of their feathers. This is being used to collect larger volumes of data on cooperative behaviours such as nest building and predator vigilance (Photo: Andre Ferreira).

MSc student Louis Bliard shakes the frost off the mist-nets during an unusually cold and wet morning at the beginning of September 2018. The study colonies are captured every year (Photo: Claire Doutrelant).

Feeding stations equipped with RFID antennas are now operating at five colonies to automatically collect data on associations between individuals (Photo: Cecile Vansteenberghe).

2017 field assistant Ryan Olinger removes a Sociable Weaver from the net during the annual captures that take place between late August and early September (Photo: Franck Theron).

A new system to collect social associations uses RFID readers to read the PIT tag numbers when the birds come to the feeders (Photo: Andre Ferreira).

A Sociable Weaver nest in the Kalahari (Photo: Phil Hockey).

Sociable weavers have a fascinating social structure, with different levels of organisation, and cooperate on multiple tasks. Our study aims to understand the evolutionary bases of these interesting behaviours (Photo: Rene van Dijk).

Wanting to study further?

The Study Opportunities page provides details for prospective students including information on the Conservation Biology Masters Course and Scholarships.