1. This thesis presents the results of a population ecology study of the Dipper Cinclus cinclus in the western Ochil Hills, Tayside and Central Regions, Scotland between April 1985 and May 1988. 2. Particular attention was given to factors affecting juvenile survival between fledging and recruitment to the breeding population. These included investigation of the variation and significance of body size, plumage colour. dispersal distance, home range acquisition, dominance status and autumn body condition. 3. Overwinter survival was higher in adults than juveniles. Juvenile females had a greater overwinter survival and recruitment rate than juvenile males. Few body size measures were consistently associated with overwinter survival,though juvenile females with longer wings and tarsi tended to survive better. 4. Males had higher plumage brightness scores than females and, within sexes, adults were brighter than juveniles. Overall, survival overwinter and recruitment were not related to plumage brightness. 5. A laboratory test arena was developed for assessing dominance relations in small groups of temporarily captive birds. Social status between age and sex classes was correlated with plumage brightness. Within age classes, plumage brightness was a significant predictor of status in adults, but body size was more important in juveniles. 6. Females settled farther from their natal sites than males; most of this dispersal was completed soon after independence. The relationship between dispersal and dominance is discussed and a model developed. 7. Autumn population density was manipulated locally in a series of experimental juvenile introductions. Numbers rapidly returned to initial levels, though earlier released individuals persisted for longer. About 20% of introduced birds recruited, mainly higher status males. 8. Body composition of a small sample of birds collected between September and April is described. Lipid stores were greatest in winter and least in spring. A method for measuring pectoralis muscle thickness was developed using an ultrasound-based technique. 9. Condition indices derived from "ultrasound" measurements on live birds were used to evaluate the importance of protein reserves in overwinter survival. Males in good condition in autumn were more likely to recruit but no trend was apparent in females. 10. Two periods of high juvenile losses were identified: post-independence and late autumn. Predation could only be implicated in the former. The agent of late autumn losses was not proven but probably involved territorial intolerance and the consequent exclusion of subordinates to fringe habitats. It is concluded that density-dependent changes in mortality, related to dominance and mediated via dispersal, caused Dipper numbers tobe matched to available resources, principally food and breeding territories.

La théorie de la sélection sexuelle a drastiquement orienté l’effort de recherche sur la communication acoustique chez les oiseaux : les mâles apprennent et produisent des chants élaborés et les femelles choisissent. Par conséquent (1) la production vocale chez les femelles a été négligée, (2) les cris (la majorité de la communication sociale) ont été peu étudiés. Contrairement aux chants, les cris ont été considérés comme innés et aucun effet de l’environnement sur leur structure n’était attendu. J’ai donc posé la question de la flexibilité vocale (court-terme) et de la plasticité vocale (au cours du développement) chez les femelles, en étudiant les cris majoritairement. J’ai étudié deux contextes où les deux sexes vocalisent: la communication dans le couple au nid et la communication parent-jeunes. Les vocalisations produites au nid par les couples montrent-elles de la flexibilité en réponse au bruit? Le développement des cris est-il influencé par l’environnement social ? J’ai travaillé sur deux espèces: le cincle plongeur, Cinclus cinclus et le diamant mandarin, Taeniopygia guttata. Chez les deux espèces, en réponse au bruit, les couples augmentent l’amplitude de leurs vocalisations. Chez le cincle une variation de la structure spectrale est observée dans les notes de chant mais pas dans les cris. Chez le diamant mandarin, les cris montrent des changements de leur structure spectrale: ils peuvent donc être flexibles en réponse au bruit. Les changements sont similaires chez les femelles et les mâles : la flexibilité n’est pas spécifique du sexe. Enfin, j’ai montré que l’environnement social précoce influence le développement des cris de quémande alimentaire chez le diamant mandarin : il existe une plasticité précoce des cris chez les mâles. J’ai montré que les femelles expriment des degrés de flexibilité similaires aux mâles mais que leur développement vocal peut prendre des trajectoires différentes. Les cris sont de bons objets de recherche pour étudier des variations de comportement vocal liées au sexe / The theory of sexual selection has drastically oriented research on acoustic communication in birds: males learn and sing conspicuous songs and females choose. Consequently, (1) female vocal production has been neglected, (2) birdcalls (most bird social communication) have been understudied. Birdcalls were supposed to be non-learned and no effect of the environment was expected on their structure (no flexibility, no learning). I thus focused my thesis on vocal flexibility (short-term) and vocal plasticity (developmental) of female vocalizations (mainly calls). I studied two contexts in which both sexes produce vocalizations: intrapair communication at the nest and parent-offspring communication. Do pairs express vocal flexibility in their calls in response to environmental noise? Is call development influenced by social environment? I studied two species: the white-throated dippers, Cinclus cinclus. (in which both sexes produce calls and songs) and the zebra finch, Taeniopygia guttata, (in which only males sing but both sexes use the same calls). I showed in both species, that in response to environmental noise, pairs increased the amplitude of their calls or song notes. In dippers, spectral flexibility was observed in song notes but not in calls. However, zebra finch calls showed spectral flexibility in response to noise. Both sexes showed similar changes in their calls: call spectral flexibility is not sex specific. Last, I showed that the structure of male begging calls changed in response to the early social environment, bringing evidence of early vocal plasticity in males. No change was found in females, showing that they either differ in their plasticity abilities or do not express plasticity because they receive different social feedbacks. My work showed that females and males show vocal flexibility but their vocal developmental trajectories may differ. Calls are thus good study objects to investigate sexual dimorphism in vocal behaviour

The doubly labelled water technique was validated for captive-bred, laying Japanese quail (Coturnix coturnix), and used to measure the energy expenditure of free-living laying swallows (Hirundo rustica). Swallows had a slightly higher energy expenditure during laying than during incubation or nestling-rearing. Energy expenditure and the net cost of incubation increased sharply for female dippers (Cinclus cinclus) when clutches were enlarged to 6 eggs. Lipophilic dyes were used to determine the rate of ovarian follicular growth and the volume of yolk deposjted in a 24 h period by captive quail and free-living swallows. Rates of yolk deposition were related to daily energy expenditure in quail, but not in swallows. Balances placed under swallow nests recorded an increase in female mass from 5 d before the first egg was laid. Female mass peaked on the evening before the first egg and declined as eggs were laid. Mass changes during laying were equal to the mass of the oviduct and developing ova. However, body composition also changed, as a lipid reserve was built up in the final 4 d before the first egg was laid, whilst body water content declined. This substantially increased the peak energy requirement for biosynthesis in a laying swallow. The lipid reserve was catabolized during the remainder of the laying period. The lipid reserve was likely to serve as an insurance against a drop in food intake during laying. Shortage of food on the day before the first egg was laid led to a reduction in clutch size for some swallows. There was no evidence for use of a protein reserve by laying swallows. A model was developed from which it was predicted that egg production by swallows, and probably all other insectivorous birds, would be constrained by energy rather than crude lipid or protein requirements. It was concluded that laying patterns and clutch sizes were sometimes constrained by food availability during egg-laying, and that an upper limit to clutch size could be set by the capacity of an incubating bird to cover the eggs.