ECR Spotlight is a series of interviews with early-career authors from a selection of papers published in Journal of Experimental Biology and aims to promote not only the diversity of early-career researchers (ECRs) working in experimental biology but also the huge variety of animals and physiological systems that are essential for the ‘comparative’ approach. Mathilde Martin is an author on ‘ Use of acoustic signals in Cape fur seal mother–pup reunions: individual signature, signal propagation and pup home range’, published in JEB. Mathilde conducted the research described in this article while a PhD student in Dr Isabelle Charrier's lab at the Institute of Neurosciences Paris-Saclay (NeuroPSI), CNRS & Paris-Saclay University, France. She is now a postdoctoral researcher in the lab of Prof. Marta Manser at the University of Zurich, Switzerland, investigating acoustic communication to decipher how vocal signals modulate social interactions in group-living mammals, in relation to the species' ecological constraints.
Mathilde Martin
How did you become interested in biology?
I've always been interested in science, with a predilection for biology and physics. One day at primary school, our teacher explained to us how to formulate hypotheses in response to a scientific question and set up an experimental protocol to test these hypotheses. I was captivated by this approach and realized that I wanted to use it to answer questions and better understand the world around us. My passion for animals naturally led me towards biology, and I soon realized that ethology was the field that excited me most. We have so much to learn from animals and how they perceive and use their environment in their everyday lives.
Describe your scientific journey and your current research focus
I began my studies with a bachelor's degree in biology at the University of Burgundy (France). At that time, my fascination with wildlife was orientated towards the marine environment, which I was lucky enough to get close to while SCUBA diving. In my third year, I hesitated between specializing in animal behaviour or marine biology, and decided to study ethology. For my master's degree, I chose to dive deeper into the oceanic environment by studying oceanography at Sorbonne University in Paris. I managed to bring my two interests together by working on mother–calf acoustic communication in humpback whales for my master’s thesis. This is where I discovered bioacoustics, the study of animal vocal communication.
After a few months of fieldwork on whales in Madagascar, I started my PhD at the Institute of Neurosciences Paris-Saclay (NeuroPSI), where I studied the vocal communication network of the Cape fur seal. For almost 4 years, I collected acoustic data and carried out playback experiments in Namibia and South Africa for several months a year to investigate how Cape fur seals exchange information through their vocalisations during the breeding season on land. A large part of my work involved assessing the degree of individuality in Cape fur seal vocalisations and investigating how individuals (females, pups, territorial males) recognise each other through their voice on the colony.
I'm now a postdoc researcher at the University of Zurich, where I am pursuing my work in bioacoustics using a terrestrial mammal study model: meerkats. I am interested in understanding how groups of meerkats maintain spatial and social cohesion during foraging by emitting and perceiving contact calls. I use a combination of acoustic and GPS data collected simultaneously on each individual of a group during foraging events.
How would you explain the main findings of your paper to a member of the public?
The Cape fur seal is one of the most colonial mammal species in the world. Breeding colonies can reach up to 210,000 individuals such as in Cape Cross, Namibia. During the breeding season, Cape fur seals make an extensive use of airborne vocalisations for communication among territorial males, among adult individuals or between a female and her single newborn pup, which makes the colonies – already very dense – very noisy and highly confusing. During this time of the year, females give birth to a single pup that they will feed with milk for 9 to 11 months. Females and pups are frequently separated during the lactation period as females regularly leave their pup on the colony to undertake multi-day foraging trips at sea. Previous studies have shown that both the mother and the pup can recognise each other's vocalisations to reunite on the colony after a maternal absence, but the acoustic features involved in this recognition process remained unknown. In this study, we performed playback experiments using artificially modified vocalisations to test which features are relevant for them to distinguish between individuals and be able to specifically recognise each other's voice. Our results showed that the mother and pup individual signature relies on a combination of many temporal and frequency parameters such as the amplitude and frequency modulations, timbre and fundamental frequency of the call. The use of such a high number of acoustic features has never been shown in a colonial species. The complexity of this vocal signature is likely to be advantageous for this species to secure the individual vocal recognition between mother and pup, crucial for the survival of the pup during period of food dependency. Other results, combining an estimate of the distance at which calls are propagated and the theoretical distance at which the pup and mother may be separated when the mother returns to the colony, show that these individuals could have strong abilities to extract vocal signals from the background noise, known as the ‘cocktail-party effect’.
Cape fur seal mothers and pups recognise each other's vocalisations, allowing them to reunite in their breeding colonies, which are among the largest in the world (photo taken at Pelican Point breeding colony in Namibia).
Cape fur seal mothers and pups recognise each other's vocalisations, allowing them to reunite in their breeding colonies, which are among the largest in the world (photo taken at Pelican Point breeding colony in Namibia).
What do you enjoy most about research, and why?
The study of animal behaviour involves a lot of fieldwork and data collection in the wild, and this is a very exciting part of the work! As naturalists, we like to spend time close to animals in their wild environment. However, to collect accurate and reliable data, we strive to minimise the impact of our presence (and/or our experiments) on the animals’ behaviour. This is an important part of our work. It's when we are out in the field, among the animals, that most of our questions are answered, but it is also when new ones come to mind! It's a never-ending process of curiosity that really thrills me.
What is the hardest challenge you have faced in the course of your research and how did you overcome it?
In certain locations, Cape fur seals can be very fearful of people, especially during their breeding season on land, where they are the most vulnerable. Approaching them at close range to be able to record their vocalizations and carry out playback experiments was the most challenging part of my PhD fieldwork. To gain the seals' trust and minimise their reaction, my colleagues and I developed a technique: we moved around the colony by crawling in the sand. When we were lying low, the seals were much less nervous and let us approach them. We tried to keep our movements slow and predictable, so as not to create a disturbance on the colony, and it worked! We used a directional microphone that would allow us to record specific individuals and be free from surrounding noise. We also used a boom about 3 m long, which we used to move equipment (such as loudspeakers) close to the seals without having to move to close to them. We also used it to ward off over-curious individuals approaching to check us out!
What is the most important piece of equipment for your research, what does it do and what question did it help you address?
As a bioacoustician, my most important piece of equipment is my microphone. Recording the vocalisations emitted by animals in various behavioural contexts is the basis for our understanding on how information is exchanged among individuals. By coupling these recordings with observations, and further acoustic analysis, we can disentangle what information is encoded in the vocal signals, how receivers extract and process this information, and how it impacts its behaviour in response. A detailed examination of each step of this process is essential to fully appreciate how and why animals communicate.
Mathilde Martin's contact details: Communication and Cognition in Social Mammals Research Group, Department of Evolutionary Biology and Environmental Studies, University of Zurich, 8057 Zurich, Switzerland
E-mail: [email protected]
