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The role of social behaviour in mate choice

Periodic Reporting for period 1 - SOCIAL MATCH (The role of social behaviour in mate choice)

Reporting period: 2021-01-01 to 2022-12-31

SOCIAL MATCH aimed to study the direct benefit of cooperation. Cooperation is at the very base of our society, and it has been argued that the adoption of cooperative breeding by our hominin ancestors provides the most parsimonious explanation for the origin of human hyper-cooperation. In addition, in humans, cooperation seems to bring not only kin benefits but also sexual benefits by influencing partner choice. Whether cooperative behaviour also influences partner choice in wild animals remains almost unknown. SOCIAL MATCH contributed to understand the principles of cooperation, and this field could and should play a role in determining policies to make our society more inclusive and reflective.
I used a cooperative bird, sociable weaver, as a model species. SOCIAL MATCH was designed to specifically test the hypothesis that cooperative behaviours co-evolve with signals indicating both identity and condition-dependent quality, with the final aim to determine whether cooperation can lead to sexual benefits for the actor.
Sociable weavers build cooperatively the largest nests among all birds, within each nest structure each breeding group possess a chamber where they live throughout the year. Whitin each breeding group related and, sometimes, unrelated individuals cooperate to feed the chicks and defend the nest. But why?
This question has bugged scientists for decades. SOCIAL MATCH main novelty - and challenge - were to develop tools to achieve a precision to quantify individual vocal behaviour and body condition never attained before. Quantifying behaviours precisely is essential to correctly interpret their meaning. With these tools we designed data collection and experiments to understand whether cooperators help only when in good condition and whether they advertise their contributions.
SOCIAL MATCH allowed the successful development of two important tools, a scale to automatically record small animal weight and individual on-board microphones to record birds’ vocalizations. These tools allow the monitoring of individual conditions and the quantification of vocal behaviour.
The scale apparatus is a modified feeder, birds sit on a perch to eat seeds but the perch is more than a simple branch, it lays on a digital scale and it is surrounded by an antenna. Each bird has a little transponder (PIT-tag) at their leg with a unique ID, like a passport, the antenna uses radio-frequency identification (RFID) technology to receive the bird’s identity which is then registered by a logger. Both the logger and the digital scale are connected to a tiny computer (a raspberry PI) which integrates and store the information about the ID and the weight. Currently, the developed system is fully functional in controlled laboratory conditions and also recording sociable weavers’ weights in the savanna of South Africa despite the challenging climatic conditions (high temperature range and often strong winds).

Individual on-board microphones are necessary to study vocalizations of each individual in a communicating group. Like each guest of a talk show has her/his own microphone, we wanted to equip each bird of a breeding group with one. This way we know what each bird say and to whom. The tiny microphones used in SOCIAL MATCH are telemetric devices meaning that they transmit radio signals. This allow to have extremely lightweight devices (0.6 grams including harness and battery) but they cannot store the signal, meaning that an antenna and a receiving system is necessary to record. We developed, for the first time, a lightweight receiving system powered by solar panel able to record in the wild.
Thanks to this system, we recorded several birds and scored their behaviour. We captured and equipped groups of four birds (2 breeders and 2 helpers) while they were cooperating to raise the offspring. We quantified their vocal and reproductive behaviour for about a week gathering extremely original and precious data, nothing similar was collected before. Currently the analysis of the vocalizations is still ongoing.
One of the strengths of SOCIAL MATCH is that it was fully integrated in the sociable weaver project (https://sociableweaverproject.com/). The sociable weaver project is a long-term project in which for several years birds and their reproductive efforts have been carefully monitored. Working within such a project allowed us to a have a lot of background information for each individual. This information will be essential to interpret the vocal behaviour recorded.
Moreover, such rich dataset provided to be a safety net when unforeseen circumstances delayed the project. Unfortunately, while I was working in the field in South Africa, a gigantic wild fire swept the field site and burned several of the monitored colonies. I lost a field season, but, thanks to already collected data, I could answer a related question to the one planned in SOCIAL MATCH. Instead of acoustic signalling, we evaluated whether the cooperation act (feeding the offspring) is used as signalling itself for potential mates. During breeding, we simulated the presence of potential mates with a playback experiment and we monitored the cooperative behaviour (feeding the offspring). If the cooperative behaviour is used as a signal, we expected the co-operators to increase their feeding rate when a potential mate was present. We found no association between the playback of an unknown individual and the rate at which birds were feeding. This means that we do not have proofs that feeding rate itself is used as a signal. However, it would still be important to monitor vocalizations during reproduction and cooperation and to develop better experimental designs to successfully answer this question. A scientific article about this data analysis is currently in the last stages of revision among co-authors and will be soon submitted to a journal.
I think that the technics developed within this project can help collect data to answer countless scientific questions in the future, way beyond the scope of SOCIAL MATCH. For example, the automation of the bird’s mass collection adds precious information about the condition of the animals. Knowing the animals’ conditions can be used in different contexts, from studying how animals cope with environmental harshness to understand how they decide whether to reproduce. Recording individualized vocalization will be important for many questions in vocal communication and bioacoustics. For example, the large dataset of individual vocalizations recorded within SOCIAL MATCH can be exploited beyond the scope of the current project to study the meaning of the different types of vocalizations.

Finally, I find that the study of cooperation in all its form is an important endeavour in basic science. At the base of several challenges that our society is facing, there is often the tragedy of the common dilemma “how to make sustainable something that everybody is free to overuse”, and it has been suggested that cooperation is a necessary step to find optimal solutions. Understanding the principles that govern the evolution and maintenance of cooperation can therefore have societal impacts.
Sociable Weaver wearing a backpack microphone. A telemetric device cable of capturing bird's voice