Tourists in Hawaii intent on seeing dolphins up close may be disturbing the animals\' daytime rest periods and driving them from safe habitats, researchers say. Researchers at Duke University studied spinner dolphins, small dolphins famed for their graceful aerial movements and balletic spins. Coastal populations of the animals divide their time between daytime rest periods in shallow, protected bays and nighttime foraging in more exposed waters, the researchers said. Repeated human disturbances during those rest periods could be driving the dolphins out of safe habitats in bays along the Hawaiian coast, they said. Only a small number of bays -- 21 out of 99 -- in a study area along the western coastlines of the main Hawaiian islands were suitable habitats for resting dolphins, said David W. Johnston, a research scientist at Duke\'s Nicholas School of the Environment. Distinguishing between sightings of resting and active dolphins was key to defining critical habitats, Duke marine scientist Lesley H. Thorne said. While socially active spinner dolphins are more tolerant of humans\' presence, she said, resting dolphins will leave the safety of a bay and retreat to less suitable open waters if they are repeatedly interrupted. \"We may be able to minimize detrimental effects on dolphins by putting restrictions or preventative measures into place in a relatively small number of bays, rather than limiting access to dolphins along the entire coast,\" Thorne said. \"That benefits tourists and tourism operators as well as the dolphins.\"