据美国《科学》杂志在线报道，它们并不是在游戏。研究人员指出，这是第一个例证，表明一种水生哺乳动物能够利用道具进行性展示。在6000多只亚马逊河豚中，研究人员发现有221只河豚——其中大多数是雄性——使用了这些小道具。雄性的这种行为往往在接近雌性时才会出现，并且主要集中在7月份——比大多数雌亚马逊河豚生育宝宝的时间提前了14个月。没有人知道亚马逊河豚的孕期到底有多长，但其他海豚和小型鲸的孕期为11到15个月。研究人员在3月25日的《生物学快报》（Biology Letters）网络版上报告了这一研究成果。（来源：科学时报 群芳）
生物谷推荐原始出处：
（Biology Letters），10.1098/rsbl.2008.0067，A.R. Martin, V.M.F. da Silva, P. Rothery
Object carrying as socio-sexual display in an aquatic mammal
A.R. Martin1, V.M.F. da Silva2, P. Rothery3
1NERC Sea Mammal Research Unit, University of St Andrews, Fife KY16 8LB, UK
2LMA, Instituto Nacional de Pesquisas da Amazônia, 69011-790 Manaus, Amazonas, Brazil
3 CEH Monks Wood, Abbots Ripton, Huntingdon, Cambridgeshire PE28 2LS, UK
Amazon river dolphins or botos (Inia geoffrensis Blainville) were observed carrying objects in 221 social groups over a 3-year study period. Sticks, branches and clumps of grass were taken from the water surface and often repeatedly thrashed or thrown. Lumps of hard clay were collected from the river bed and held in the mouth while the carrier rose slowly above the surface and submerged again. Carriers were predominantly adult males and less often subadult males. Adult females and young dolphins rarely carried objects. Groups of dolphins in which object carrying occurred were differentially large and comprised a greater proportion of adult males and adult females. Aggression, mostly between adult males, was significantly associated with object carrying. The behaviour occurred year-round, with peaks in March and July. A plausible explanation of the results is that object carrying by adult males is aimed at females and is stimulated by the number of females in the group, while aggression is targeted at adult males and is stimulated by object carrying in the group. We infer that object carrying in this sexually dimorphic species is socio-sexual display. It is either of ancient origin or has evolved independently in several geographically isolated populations.
