(PhysOrg.com) -- Scientists studying dolphin behavior have suggested they could be the most intelligent creatures on Earth after humans, saying the size of their brains in relation to body size is larger than that of our closest relatives, the chimpanzees, and their behaviors suggest complex intelligence. One scientist said they should therefore be treated as "non-human persons" and granted rights as individuals.

The behavioral studies showed dolphins (especially the bottlenose) have distinct personalities and self-awareness, and they can think about the future. The research also confirmed dolphins have complex social structures, with individuals co-operating to solve difficult problems or to round up shoals of fish to eat, and with new behaviors being passed from one dolphin to another.

Several examples of learning being passed on to other individuals have been observed. In one case a rescued dolphin in South Australia, taught to tail-walk during recuperation, in turn taught the trick to other wild dolphins in the Port Adelaide river estuary when she was released. According to marine biologist Mike Bossley it was "like watching a dance craze take off", with the dolphins apparently learning the trick just for fun, since tail-walking has no natural function.

Work carried out by professor of psychology at the City University of New York, Diana Reiss, showed dolphins could recognize themselves in a mirror, and could use it to inspect other parts of their bodies, an ability previously only demonstrated in humans and a few animals such as apes, elephants and pigs. In another study Reiss was able to teach captive dolphins a rudimentary language based on symbols.