No abstract

Tool use is rare in wild animals, but of widespread interest because of its relationship to animal cognition, social learning and culture. Despite such attention, quantifying the costs and benefits of tool use has been difficult, largely because if tool use occurs, all population members typically exhibit the behavior. In Shark Bay, Australia, only a subset of the bottlenose dolphin population uses marine sponges as tools, providing an opportunity to assess both proximate and ultimate costs and benefits and document patterns of transmission. We compared sponge-carrying (sponger) females to non-sponge-carrying (non-sponger) females and show that spongers were more solitary, spent more time in deep water channel habitats, dived for longer durations, and devoted more time to foraging than non-spongers; and, even with these potential proximate costs, calving success of sponger females was not significantly different from non-spongers. We also show a clear female-bias in the ontogeny of sponging. With a solitary lifestyle, specialization, and high foraging demands, spongers used tools more than any non-human animal. We suggest that the ecological, social, and developmental mechanisms involved likely (1) help explain the high intrapopulation variation in female behaviour, (2) indicate tradeoffs (e.g., time allocation) between ecological and social factors and, (3) constrain the spread of this innovation to primarily vertical transmission.

No abstract

Foraging behaviors of bottlenose dolphins vary within and among populations, but few studies attempt to address the causes of individual variation in foraging behavior. We examined how ecological, social, and developmental factors relate to the use of a rare foraging tactic by wild bottlenose dolphins (Tursiops sp. Gervais, 1855) in Shark Bay, Western Australia. Beach hunting involves partial and nearly complete stranding on beach shores. Over 10 years of observation, only four adults and their calves were observed beach hunting in more than 1 year. Of two adult beach hunters observed in detail, one was more specialized in beach hunting than the other, indicating substantial flexibility in degree of use. Only calves born to beach hunters developed the tactic, although complete stranding was not observed at least up to 5 years of age. Beach hunters used shallow, inshore habitats significantly more than others and were more likely to hunt during incoming tide. Mitochondrial DNA haplotypes were not consistent with strict matrilineal transmission. Thus, beach hunting likely involves vertical social learning by calves, while individual, horizontal, and (or) oblique learning may occur among individuals who frequent coastal habitats. Résumé :Les comportements alimentaires des grands dauphins varient à l'intérieur d'une population et d'une population à une autre, mais peu d'études s'intéressent aux causes de la variation individuelle du comportement alimentaire. Nous examinons comment les facteurs écologiques et sociaux et le développement influencent l'utilisation d'une tactique inusitée de recherche de nourriture chez les grands dauphins (Tursiops sp. Gervais, 1855) à Shark Bay, Australie Occidentale. La chasse sur la grève implique un échouement partiel ou presque total sur les plages de la côte. En 10 années d'observation, seuls quatre adultes et leurs petits ont été observés à chasser sur la grève plus d'une année. Des deux adultes observés en détail chassant sur la grève, un était plus spécialisé pour la chasse sur la grève que l'autre, faisant montre d'une grande flexibilité dans l'importance de l'utilisation qu'il en faisait. Seuls les petits nés de parents qui chassaient sur la grève développent cette tactique, bien que l'échouement total ne s'observe pas avant l'âge de 5 ans. Les chasseurs de grève utilisent les habitats peu profonds près des côtes significativement plus que les autres et ils sont plus susceptibles de chasser durant la marée montante. Les haplotypes d'ADN mitochondrial n'appuient pas une transmission matrilinéaire stricte. La chasse sur la grève implique donc vraisemblablement un apprentissage social vertical par les petits, alors qu'il peut se produire un apprentissage individuel, horizontal et(ou) oblique chez les individus qui fréquentent les habitats côtiers peu profonds.[Traduit par la Rédaction] Sargeant et al. 1410

No abstract

Aggressive behaviour is rarely observed, but may have a large impact on the social structure, relationships and interactions in animal societies. Long-term behavioural study of Indian Ocean bottlenose dolphins in Shark Bay, Australia, suggests that males are more aggressive than females, and use sexual coercion during the breeding season, but age and sex-specific patterns of aggression have not been well documented. We analyzed tooth rake marks, an indirect measure of received conspecific aggression, to determine such patterns by age, sex, and adult female reproductive state. Photographs of 224 Shark Bay bottlenose dolphins were examined for tooth rakes and each rake was categorized as new (broken skin), obvious (white rake lines that are clearly visible) or faint (faint evidence of rakes). Rake lines were also coded by each body section visible in the photograph. Cycling females (those that became pregnant within 6 mos. of the photograph date) were significantly more likely to have new tooth rakes than non-cycling females (pregnant or with a dependent calf <20 mos.). Adult males were significantly more likely to have tooth rake marks than adult females, with the same tendency for juveniles. Calves, with far fewer rakes than any age class, showed no significant sex difference. Body coverage of tooth rakes was significantly more extensive for adult males than for adult females, but there were no sex differences on coverage for juveniles or calves. Comparison of tooth rakes at two periods during adulthood (>2 years apart) suggests that the marks are not cumulative. Overall, 83% of the population has tooth rake marks, suggesting that agonistic interactions occur for most individuals at least every two years. Analysis of agonistic interactions for 55 adult focal females (observed for 1960 h) and their 88 calves

No abstract

No abstract