Isabelle Charrier Team
• 1) Dynamics of vocal activity and social network
Acoustic communication plays a fundamental role in survival and reproduction in many species. Acoustic signals are involved in recognition of individuals, kin, species, but also in mate selection and parental care. These signals are furthermore essential to coordinate collective behaviour in group-living species (i.e., foraging, shelter seeking, and predator avoidance). The development of advanced technology instruments in the last decade, such as acoustic tags, has brought new opportunities and insights in the study of animal behaviour. Using acoustic tags coupled to different sensors (either hydrophone coupled with time-depth recorder, 3D accelerometer and 3D magnetometer for marine species, or microphone coupled with GPS and video camera for aerial and terrestrial species), researchers can now assess how animals behave during social interactions in their natural environment.
Using such acoustic tags is of primordial interest for species for which a knowledge gap on the social/vocal behaviour exists, such as mother-young interactions in marine mammals, vocal interactions of seabirds during foraging trips at sea, and vocal activity of terrestrial birds. Currently, we still don’t know the complete vocal repertoire of marine species, and the biological function of their vocal production. Understanding how they organize their social activities especially during the breeding season (mate guarding, courtship), but also if they use vocal signals to advertise their conspecifics of any potential dangers, disturbances or predators will bring new knowledge and open a wide range of additional research questions. We have initiated different projects these last 3 years on birds, seabirds, whales and pinnipeds.
• 2) Vocal Production modelling
Understanding how the vocal messages are encoded by particular acoustic parameters requires an analysis of the biomechanics of the vocal production organ. Yet, if the detailed functional analysis of the vocal organ – the syrinx – has been reconstructed very recently in songbirds, such model, necessary for the understanding of the biomechanics of sound production and function, does not yet exist in non-songbirds (half of the bird species). Propagation computing tomography will serve as a basis to construct high-resolution three-dimensional images of the anatomical structures and to model the complete system of vocal production in these birds. Our study will provide new insights in how non songbirds are able to control independently the two sides of their vocal organs to produce two voices and to emit low frequency sounds, bringing a piece to our understanding of the evolution of vocal communication in Vertebrates.
Vocal production in marine mammals, especially in mysticetes, is still totally unknown. Since 2011, we investigate how whales produce these sound units, and we have identified 2 vibrators (arytenoids and corniculate flaps), 2 air sources (lungs and laryngeal sac), and 2 resonators (nasal cavities and laryngeal sac) in their respiratory system. We made the link between the acoustic features of the sound units (time and frequency modulations) and the functional anatomy of the larynx. We introduced the 4L model (low, loud, long, and loquacious). We are also focussing on vocal non-linearities (frequency jumps, chaotic segments) in sound units, and suggest that such non-linearities phenomena could be either explained by anatomical differences among individuals, or by intentional vocal expression or by a lack of well-controlled vocal production. Finally, we are investigating the different roles of the respiratory system components, especially the laryngeal sac that seems to be involved in breathing, duration of apnea, sound production and buoyancy as it acts as active ballast during diving.
• 3) Communication strategies in regards to social and physical constraints
We aim to decipher the communication strategies used by species facing similar constraints (noisy or obstructed environments) using an uni- and multi-modal approach. Communication is multi-modal, so this is essential to consider all sensory modalities in communication, and thus study their interactions. The final aim being to suggest rules of communication in Vertebrates.
NOISE – In animals, recognition between individuals is essential to the settlement of sexual and social relationships. Due to their physical properties and their potentiality to encode any kind of information, sounds are an effective mean to reliably transmit the identity of the emitter. Nevertheless, in colonial animals, the vocal signal an adult produces when seeking its young or its partner among thousands of individuals is transmitted in a context involving the noise generated by the colony. This background noise drastically reduces the signal-to-noise ratio and masks the signal by sounds with similar spectral and temporal characteristics. We investigate in colonial bird and mammal species how this extreme acoustic environment constrains the transfer of acoustic information. We examine solutions found at the level of the emitter to improve the efficiency of communication and we report how the receiver can optimize the collected information.
OBSTRUCTED HABITAT – Dense forests represent constraining acoustic channels. In this obstructed environment, sounds are modified during propagation by various processes such attenuation, reverberations, frequency filtering and scattering. In spite of these propagation-induced alterations of the sound, acoustic communication remains effective. The aim of our research is first to characterize the modifications of acoustic signals during transmission, and second to understand how birds manage with these environmental constraints to communicate at long rate. For a comparison purpose, we focus both on temperate and tropical forest songbirds.
• 4) Female singing behaviour
The songs of songbirds are learned signals supporting different types of information, encoded at different structural levels by different acoustic parameters, crucially involved in territorial and sexual contexts. Male and female singing is common in the majority of sub-tropical and tropical species investigated so far and is thought to be the ancestral state in the evolutionary story of songbirds but female singing is rare in temperate species in which only males sing. This raises questions on the selective pressures acting on bird singing in temperate species, and on the neuro-physiological mechanisms of both learning and production.
From numerous years, the team is implicated in bird scaring by mean of acoustic methods. Thus, we have patented an acoustic system to move some bird species (gulls, crows, lapwings, starlings, doves) away from runways. This system, based on the use of synthetic distress calls, is used with success by most of the important European airports. Currently, we are working on a method to reduce bird strike risk thanks to an acoustic system embedded on aircraft (Bird Impact Repellent & Deterrent sYstem R&T project with AIRBUS Industry group).
Acoustic survey & Conservation
Being not invasive and allowing investigation in dark or obstructed environments, acoustics can be a powerful tool of wildlife assessment. Currently, our activity focuses on two main questions :
• 1) surveying biodiversity in tropical rainforest and
• 2) following individuals within bird and pinniped populations.