The Common River Frog Amietia quecketti is a well-known and widely distributed species in southern Africa. Despite the fact that it is a common species and quite prevalent in urban areas little is known about its behaviour. The North-West University Botanical Gardens was selected as study area as it supports a healthy population of Common River Frogs at a series of 18 water bodies. Each pond in the Garden was assigned a reference number and the surface area, depth and vegetation were noted. Frogs were located with the aid of strong flashlights. Specimens were caught by hand and transferred to clear plastic bags. Frogs were sexed and their mass and their snout-vent length (SVL) were determined. Frogs were subsequently individually marked by means of injecting a micro-transponder (pit-tag) subcutaneously. Field observations were conducted over two consecutive evenings every two weeks for a period of one year. On the first night all sites were visited and all frogs were scanned and their position, orientation and activity were noted. During the second night focus was on Pond 6 as it sustained the biggest population. Observation started at 19:15 and continued until 02:30. All frogs in and around the pond were scanned and detailed notes were taken, focusing on their orientation, behaviour, calling activity and distance to the nearest other frog. Results showed that limited movement between ponds in the Garden does occur. A number of individuals were recorded regularly. Some males had preferred call sites, and clear circadian and seasonal patterns with regards to males and females exist. The complex call structure consist of a chuck and a whine and then a combination of the two. / MSc (Environmental Sciences), North-West University, Potchefstroom Campus, 2013

The Common River Frog Amietia quecketti is a well-known and widely distributed species in southern Africa. Despite the fact that it is a common species and quite prevalent in urban areas little is known about its behaviour. The North-West University Botanical Gardens was selected as study area as it supports a healthy population of Common River Frogs at a series of 18 water bodies. Each pond in the Garden was assigned a reference number and the surface area, depth and vegetation were noted. Frogs were located with the aid of strong flashlights. Specimens were caught by hand and transferred to clear plastic bags. Frogs were sexed and their mass and their snout-vent length (SVL) were determined. Frogs were subsequently individually marked by means of injecting a micro-transponder (pit-tag) subcutaneously. Field observations were conducted over two consecutive evenings every two weeks for a period of one year. On the first night all sites were visited and all frogs were scanned and their position, orientation and activity were noted. During the second night focus was on Pond 6 as it sustained the biggest population. Observation started at 19:15 and continued until 02:30. All frogs in and around the pond were scanned and detailed notes were taken, focusing on their orientation, behaviour, calling activity and distance to the nearest other frog. Results showed that limited movement between ponds in the Garden does occur. A number of individuals were recorded regularly. Some males had preferred call sites, and clear circadian and seasonal patterns with regards to males and females exist. The complex call structure consist of a chuck and a whine and then a combination of the two. / MSc (Environmental Sciences), North-West University, Potchefstroom Campus, 2013

Chez les espèces sociales, les vocalisations transmettent des informations qui participent au maintien et à la survie du groupe. Alors que de nombreuses études se sont intéressées aux informations stables portées par les vocalisations telles que l’identité, peu d’études se sont interrogées sur le rôle des signaux vocaux dans la transmission des informations plus labiles, telles que l’état émotionnel de l’émetteur. Le stress est un bon candidat pour l’étude de l’expression des émotions chez les animaux, puisqu’il est directement mesurable via un dosage de la concentration plasmatique en glucocorticoïdes. Le stress est connu pour modifier les paramètres acoustiques des vocalisations chez les mammifères, mais peu d’études ont traité ce processus chez les oiseaux, qui présentent pourtant des réseaux sociaux complexes. Le but de cette thèse est de déterminer de quelle manière les oiseaux expriment vocalement leur stress, et d’évaluer dans quelle mesure la corticostérone, hormone de stress principale chez l’oiseau, est impliquée dans le phénomène. Je me suis intéressée au Diamant mandarin (Taenopygia guttata), un oiseau chanteur australien au comportement grégaire qui forme des liens d’appariements à vie et prodigue des soins biparentaux à sa progéniture. En administrant de la corticostérone exogène à des oiseaux et en utilisant également des évènements sociaux stressants, nous montrons que les mâles adultes et les poussins expriment leur stress à travers l’émission de cris modifiés dans leur structure, ce qui suggère que la flexibilité des cris chez les oiseaux est plus importante que l’avaient montré des études précédentes. Par une analyse complète des paramètres temporels et spectraux des cris, nous montrons pour la première fois que le stress, par un effet direct de la corticostérone, déclenche l’émission de vocalisations présentant un spectre de fréquence déplacé vers les hautes fréquences. De plus, les receveurs du signal (respectivement les partenaires femelles et les parents) semblent capables de décoder l’information portée par ces cris de stress car ils modifient leur comportement en conséquence. Les processus physiques impliqués dans l’émission de cris modulés par le stress sont également discutés en appliquant la théorie « source-filtre » généralement utilisée chez les mammifères. Enfin, les valeurs adaptatives de ces cris sont également envisagées, en rapport avec le réseau social du Diamant mandarin et les risques de prédation encourus par l’émetteur du signal. Ce travail apporte de nouvelles preuves sur l’expression du stress chez les oiseaux, et propose une étude complète, des signaux physiologiques impliqués dans le stress aux modifications de comportement de l’émetteur, qui déclenchent une réponse adaptative des receveurs du signal / In social species, vocalisations convey information that participates in the maintenance and the survival of the group. While many studies were interested in stable information carried by vocal signals, like identity, fewer studies dealt with their potential role in informing about labile information such as the senders’ emotional state. Stress is a good candidate for the study of the expression of emotions in animals, as it is directly measurable by the plasma levels of glucocorticoïds. Stress is known to modify acoustic parameters of vocalisations in mammals, but few studies studied the process in birds, that also show complex social networks. The aim of this thesis is thus to determine how birds can vocally express their stress and to what extent corticosterone, the main stress hormone in birds, is implicated in this expression. I focused my research on the zebra finch (Taenopygia guttata), a gregarious Australian songbird that form lifelong pairbond and provides biparental care to its young. Using oral administration of exogenous corticosterone but also social stressful events, we show that both adult males and nestlings can express their stress through modulations of their calls’ structure, suggesting that flexibility in birds’ vocalisations is higher than previously expected. With a complete analysis of temporal and spectral parameters of calls, we show for the first time that stress evokes the emission of vocalisations with up-shifted frequency spectrum via a direct effect of corticosterone. Moreover, we show that females and parents are able to decode the information carried by stressed-induced calls of respectively their male partner and their young, as they exhibit modifications of behaviour in accordance with the context. The physical processes leading to the emission of stressed-induced vocalisations are discussed by applying the source-filter theory usually used in mammals. Adaptive values are also proposed, in regards with the zebra finch social network and predation risks for the caller. This work gives new evidences about the expression of stress in birds, and proposes a comprehensive study, from the physiological signals involved in stress to the resulting modifications of communication behaviour for the sender, that leads to an adaptive response from the receivers