Abstract: Similar to terrestrial mammals, male-female sexual behavior is significant for the survival and continuation of certain cetacean species. However, non-reproductive mating behaviors, i.e. homosexual behaviors and masturbation, are widespread in all mammals. Therefore, it would be interesting and helpful to better understand the reproduction of cetaceans by further investigating their non-reproductive behaviors. We investigated male and female non-reproductive behaviors in a captive population of Yangtze finless porpoise including three males and four females. Fourteen sexual behaviors were defined in our sexual behavioral ethogram, and the occurrence frequencies and dyads of each non-reproductive behavior were recorded. Over half of the sexual behaviors were non-reproductive behaviors (3887 times, 69.87%); homosexual behaviors occurred 3633 times (65.31%) and masturbation was recorded 254 times (4.57%). Most homosexual behaviors were performed between males (3438 times, 94.63%). The dyads AFU & TAO (1921 times, 55.88%) were the most active dyads involved in male-male sexual behaviors, and most of these behaviors (1543 times, 80.32%) were cooperative by counterpart. The male homosexual behaviors are thought to be related to the gang coalition or training. One female-female pair (F7 & F9; 117 times; 60.00%) performed the most frequent homosexual behaviors. None of the female-female sexual behaviors were rejected by the counterpart. Female homosexual behaviors, however, may have something to do with company or communication.

Key words: Captive, Ethogram, Homosexual behavior, Masturbation, Yangtze finless porpoise

摘要： 雌雄性之间的性行为对鲸类的生存和繁衍有着极其重要的意义。然而不具有繁殖功能的同性性行为和自慰行为在多种鲸类中存在。因此对鲸类非繁殖性性行为研究，将有助于深入认识该物种性行为特点和规律，并解决室内饲养可能存在的问题以及促进可控性人工繁殖的成功。本研究以人工饲养的7头长江江豚为研究对象，定义并描述了14种性行为。其中，同性之间的性行为定义为同性性行为，雌雄个体单独的性行为定义为自慰行为。雄性同性性行为发现于所有定义的性行为中，但雌性同性性行为仅在7种性行为中观察到。同性性行为（3633次）占总性行为（5563次）的65.31%，自慰行为（254次）占4.57%。同性性行为中，雄性之间的同性性行为（3438次，94.63%）远多于雌性同性性行为（195次，5.37%）。两头有父子关系的江豚（阿福和淘淘）之间的雄性同性性行为最多（1921次，55.88%），雄性江豚之间的同性性行为可能存在结盟竞争关系或教育练习作用。两头青少年雌豚（F7和F9）之间的同性性行为最活跃（117次，60.00%），雌性江豚之间的同性性行为很可能具有结伴交流的功能。

关键词: 长江江豚, 豢养, 行为谱, 同性性行为, 自慰