Diurnal behavior of free-ranging bottlenose dolphins in the Kvarneric (northern Adriatic Sea)

The diurnal behavior of a bottlenose dolphin (Tursiops truncatus) community was observed from small inflatable craft between 1987 and 1994. Following a preliminary ad libitum study 11,839 S-min behavioral samples were recorde d in 1991-1994. The behavioral budget showed a predominance (about 80%) of activities characterized by long (>30 sec) dives, considered to be largely related to prey search or feeding. Obvious foraging near the surface was ob served rarely. The frequent following of trawlers (accounting for 4.6% of t he behavioral budget) was indicative of the presence of alternative strateg ies for finding food. Yearly and seasonal behavioral variation-particularly in feeding-related and travel behaviors-was consistent with the hypothesis of behavioral flexibility as a response to environmental changes and fluct uating prey kind and availability. Yearly shifts in social behavior appeare d to be partly influenced by breeding cycles. Groups engaged in feeding-rel ated activities were significantly smaller than traveling or socializing gr oups, and dramatic interannual group-size shifts seemed to be largely affec ted by environmental variables, rather than being entirely determined by be havioral activity changes. The remarkable behavioral flexibility of this bo ttlenose dolphin community may contribute to its survival in the shifting e nvironmental conditions of the northern Adriatic Sea. However, the high pro portion of time consistently devoted to feeding-related activities, as comp ared to other areas, suggests that food resources in the Kvarneric were not only highly variable but also depleted.