Dear colleagues, Two new papers on the ecology and behavior of (island-associated) tropical dolphins have been published recently: Kiszka, J., Simon-Bouhet, B., Martinez, L., Pusineri, C., Richard, P., Ridoux, V. 2011. Ecological niche segregation within a community of sympatric dolphins around a tropical island. Marine Ecology Progress Series, 433: 272-288. Investigating ecological segregation among organisms of a given community is challenging, especially when these organisms share similar patterns of distribution, and similar size and morphology. Around the island of Mayotte, a diversified community of at least 4 sympatric delphinids is present year round within a very restricted range: the Indo-Pacific bottlenose dolphin Tursiops aduncus, the spinner dolphin Stenella longirostris, the pantropical spotted dolphin S. attenuata, and the melon-headed whale Peponocephala electra. In addition, the Fraser’s dolphin Lagenodelphis hosei makes temporary incursions into peri-insular waters as well. This study aims to assess niche segregation among this tropical dolphin community. We hypothesized that each species occupies its own distinct niche defined by the following axes: habitat, resources and time. We analysed habitat in relation to physiography, behavioural budgets and C and N stable isotope values from skin and blubber samples for each species. The results highlighted that habitat and behavioural budgets were relatively distinct among species, with few exceptions. However, in those species living on the outer reef slope where habitat and behaviour were not well discriminated, stable isotope analyses confirmed that species have different trophic levels (mostly reflected through δ15N values) or foraging habitat (mostly reflected through δ13C values). This study confirms that the use of multiple methodologies (habitat, behaviour and feeding ecology studies) help in discerning ecological niche segregation, especially when examining closely related species within a common restricted range. Kiszka, J., Perrin, W.F., Pusineri, C., Ridoux, V. What drives island-associated tropical dolphins to form mixed-species associations in the southwest Indian Ocean? Journal of Mammalogy, 92: 1105-1111. Mixed-species associations are temporary aggregations of individuals of different species involved in similar activities. Such associations form for foraging, protection against predators, and social advantage. Mixedspecies groups in delphinids are frequent in the wild. We aimed to understand the ecological significance of mixed-species group formation by 2 tropical delphinids, the spinner dolphin (Stenella longirostris) and the pantropical spotted dolphin (Stenella attenuata), in waters surrounding the island of Mayotte in the southwestern Indian Ocean. We used sighting data collected year-round from 2004 to 2009. We encountered a total of 67 mixed-species groups (comprising 21% of all groups observed) of spinner and pantropical spotted dolphins around Mayotte. No daily or seasonal variability in the occurrence of associations was detected. Behavioral activities of single- and mixed-species groups differed significantly. Foraging was observed only in single-species groups of pantropical spotted dolphins. Mixed-species groups were larger than single-species groups. When in association, spinner dolphins used deeper waters than while in single-species groups. No evidence of association for social advantage was observed. We suggest that spinner dolphins associate with spotted dolphins for protection against predators when transiting between resting areas. Please do not hesitate to contact me for further information (jeremy.kiszka@wanadoo.fr). Regards, Jeremy Kiszka Jeremy Kiszka (PhD) South-West Indian Ocean Fisheries Project (SWIOFP) Project coordinator Université de La Rochelle, lab. LIENSs (UMR 6250) Institut du Littoral et de l'Environnement, 2 rue Olympe de Gouge, F-17000 La Rochelle. Tel. +33(0)546076898 Mobile +33(0)681432009 Skype: jeremy.kiszka