By Aldemaro Romero

When we go to a zoo or an aquarium, one of the most delightful images is that of young animals playing with each other. We relate to that; after all, we do it throughout our entire life in one way or another.

Behavioral scientists have known for years that playing is used by many animal species, particularly mammals and birds, as a form of practicing certain behaviors for later in life: from fighting to hunting. But now some research is providing new light on how the ritual of playing is being passed from parents to progeny among dolphins.

In the latest issue of the scientific journal, Behavioral and Brain Sciences, researchers from the University of Southern Missouri reported a startling behavioral observation among rough-toothed dolphins off the coast of Honduras. They saw two adults and a young dolphin passing a plastic bag back and forth, as in a game of catch.

What really caught the researchers attention was the fact that when the adults passed it to the young dolphin, they did so more carefully than to each other, releasing it just in front of the youngster's mouth, as if to make it easier to catch.

During five years of research with captive bottlenose dolphins, other scientists have observed that bottlenose dolphins were making their games increasingly difficult in a progression that seemed to be aimed at teaching the young.

But this behavior is not only a way to teach the young new tricks; it can also pass traditions from one generation to another helping cultural transmission among animal species.

Researchers have observed that the way certain tools are used by chimpanzees tends to vary from one family group to another. Those methods are passed through teaching. Apparently many of the new tricks are initiated by youngsters entering adulthood, after which these new abilities are passed on to the entire family group.

One of the most exceptional and observed dolphin behaviors is that of bowriding -- the swimming right in front of boats. Dolphins use the myriad of skin sensors they have in order to calculate where in front of the boat the wave pressure is at a maximum so they can take advantage of the moving boat and be "pushed" forward.

This year, during spring break, an entire class of Arkansas State University students attended a field marine mammals course that took place off the coast of Key West. They observed one of the longest bowriding events ever registered for bottlenose dolphins -- 16 minutes and 55 seconds.

During that time the dolphins involved in the event traveled 7.2 km (3.4 nautical miles) in front of the boat. The interesting thing is not only that this is a learned behavior (after all boats are a rather recent invention by humans) but when this group of ASU students observed that behavior, always both adults and youngsters were involved, with the adults leading the way.

As soon as the adults stopped bowriding, so did the youngsters. Obviously the latter were following the lead of the former.

Nowadays research is being aimed also at understanding how information is passed among individual dolphins. I videotaped and recorded the behavior and sounds of bottlenose dolphins in the Minnesota Zoo for two years. It was remarkable to see how certain communication sounds (mostly whistles) produced by dolphins were accompanied by body language as if the dolphins were trying to emphasize with their postures certain acoustic messages.

This is remarkable because unlike humans and other primates dolphins do not have arms and lack facial expressions beyond just opening their mouths. Yet they were flexing their body and changing their postures as to emphasize a vocal message.

There is much more than we think behind the dolphin's eternal smile.

For more information contact the ASU Department of Biological Sciences at biology@astate.edu.

Dr. Romero is chairman and professor of biology at ASU.