L’objectif de la thèse a été d’étudier la structure, la fonction et la plasticité au cours du temps du chant d’un oiseau mâle adulte, la fauvette à tête noire Sylvia atricapilla. L’influence de différents comportements migratoires sur les caractéristiques du chant, sur la maintenance des dialectes et sur l’apprentissage a également été étudiée chez deux populations, une migratrice (représentée par 2 groupes à Paris) et une sédentaire (représentée par 3 groupes en Corse). Le chant de cette espèce est constitué de deux parties aux caractéristiques acoustiques bien distinctes, le warble et le whistle. Nos expériences de diffusion montrent que chacune des deux parties peut provoquer une réponse territoriale des mâles. Ce chant en deux parties permet probablement aux fauvettes de transmettre des informations différentes, destinées à différents auditoires, proches et lointains, mâles et femelles. Nos analyses génétiques par microsatellites ne montrent pas de structure génétique des groupes et populations. Néanmoins, nous avons montré l’existence de variations micro-géographiques au niveau de la composition en syllabes et en séquences de syllabes de cette seconde partie du chant. Bien que le renouvellement des individus soit plus important chez les migrateurs que chez les sédentaires, les 2 populations ont un taux de partage de syllabes et de phrases équivalent au sein des groupes. Nous avons cependant observé que les individus migrateurs ont un répertoire de syllabes 2 fois plus grand mais une diversité de phrases partagées 2 fois moins grandes que les sédentaires. Le suivi d’individus sédentaires sur plusieurs années consécutives a permis de montrer que l’espèce faisait preuve d’une plasticité vocale puisqu’on observe un plus grand partage de syllabes et de phrases intra année qu’inter année au sein des groupes. Même si les individus semblent modifier le contenu de leurs chants chaque année, nous n’avons pas réussi à mettre en évidence par des expériences de diffusion en milieu naturel un apprentissage à l’âge adulte de nouvelles syllabes ou de nouvelles phrases. / The aim of the thesis was to study the structure, function and plasticity over time of the song of a male adult bird, the blackcap Sylvia atricapilla. The influence of different migratory behaviors on the song characteristics, on the dialect maintenance and on learning has also been studied in two populations, a migratory one (represented by two groups in Paris) and a sedentary one (represented by 3 groups in Corsica). The song of this species consists of two parts with distinct sound characteristics, the warble and the whistle. Our playback experiments show that both parts trigger male territorial response. Such a song in two parts probably allows blackcaps to transmit different information for different audiences, close and distant, males and females. Genetic analyzes with microsatellites show no genetic structure of groups and populations. Nevertheless, we have shown the existence of micro-geographical variations in the composition of syllables and sequences of syllables in the whistle part. Although the turnover of individuals is higher among migrants than among sedentary populations, the two populations have similar syllables and phrases sharing within groups. However, migratory birds, compared to sedentary ones, have a syllable repertoire size twice as large and a repertoire of phrase sharing much smaller. The survey of sedentary individuals over several consecutive years has shown that the species show a vocal plasticity since a greater sharing of syllables and of phrases is observed intra year than between years within groups. Although individuals seem able to modify their songs every year, we didn’t succeed in showing with playback experiments in natural environment that adults males were able to learn new syllables or new phrases.

Oxycarenus lavaterae is species of Heteroptera and possessing pink blots on corium and distinctive, gleaming membranaceous wings. This appearance could correspond to the definition of a warning color. The design is similar to other coreoid Heteroptera, which live in the Czech Republic; though Oxycarenus lavaterae is a species originating from Mediterranean and quickly spreading north. In Czech Republic it is a new species and predators thus have only short experience with it.The information about chemical protection of Oxycarenus lavaterae is weak and the effect on predators has never been tested. The characteristic behaviour for this species is creating large aggregations, primarily at the time of hibernation. At that time, several thousands of individuals are gathered in apertures or at the surface of tree bark. The aggregation may enhance the warning appearance of this species. The aim of this study was to test the response of bird predators to the adult individuals of Oxycarenus lavaterae. Three species of insectivorous birds differing in the level of foraging and diet specialization was chosen as predator (namely - Great tit (Parus major), Blue tit (Cyanistes caeruleus), Eurasian blackcap (Sylvia atricapilla)). Unmodified individuals of Oxycarenus lavaterae were served to these predators. In the case of the Parus major, the aggregation of Oxycarenus lavaterae (about 100 pieces) was also presented to test the effect of gregarious behavior on the warning signal. This study showed that the Parus major and the Sylvia atricapilla attacked the individual Oxycarenus more often than the Cyanistes caeruleus showing high level of restraint. In experiments with aggregatedOxycarenus lavaterae Parus major attacked them less often than when presented solitarily. However, after eating some Oxycarenus lavaterae, the Parus major showed symptoms of disgust and loss of appetite.