Mystery of the Silver Rings
by Don White, Creator of Project Delphis
The young dolphin gives a quick flip of her head, and an undulating silver ring appears--as if by magic--in front of her. The ring is a solid, toroidal bubble two feet across--and yet it does not rise to the surface! It stands erect in the water like the rim of a magic mirror, or the doorway to an unseen dimension. For long seconds the dolphin regards its creation, from varying aspects and angles, with its vision and sonar. Seemingly making a judgement, the dolphin then quickly pulls a small silver donut from the larger structure, which collapses into small bubbles. She then "pushes" the donut, which stays just inches ahead of her rostrum, perhaps 20 feet over a period of up to 10 seconds. Then, stopping again, she regards the twisting ring for a last time and bites it--causing it to collapse into a thousand tiny bubbles which head--as they should--for the water's surface. After a few moments of reflection, she creates another.
This isn't fantasy, it's real. And it isn't magic, just marvelous. It is a rare dolphin behavior, and we first saw it in the play of two baby dolphins. It gives us a little more insight into the superb level of control dolphins can exercise on their water environment, and underscores the fact that we can still discover things about dolphins by simply watching them.
I first saw this behavior on one of my relatively rare trips out to the Delphis lab; the project's principle scientist Ken Marten said that "the two babies, Tinkerbell and Maui" had been doing it for a little while. My reaction: "Wow, neato. How the heck do they DO that? Try to get some photo and video shots of it. It sure is cool". Ken, along with Suchi Psarakos, Research Assistant and computer programmer, did indeed document the silver rings (although video and photos don't do the rings justice), and this has made it possible to both analyze the physics behind the phenomenon and to watch the dolphins do this trick in slow-motion.
As it turned out, small silver rings weren't the only toys the dolphins were making for themselves: some of the creations were as large as a basketball rim. And Tinkerbell proved able to create a silver helix, spiraling perhaps 20 feet long, that would spring into life in a fraction of a second and remain stable in the water as she swam past, observing it with sonar and vision. then--presto! she would grab a small silver ring from the helix to play with, while the rest of the helix degraded into bubbles which would belatedly "remember" to rise to the surface.
This was a wonderful mystery to ponder. My attempts at re-creating the rings in a swimming pool succeeded only in getting water up my nose, but my guesses were confirmed--with better and more rigorous explanation--by the fluid dynamics class of Suchi's close friend Hans Ramm at Scripps Institute of Oceanography.
The silver rings, as it turns out, are "air-core vortex rings", and the helices are a similar phenomenon. Invisible, spinning vortices in the water are generated from the tip of a dolphin's dorsal fin when it is moving rapidly and turning. According to Hans: "Being unstable without a boundary nearby, the vortex line tends to form into a more stable form such as a helix. When the dolphins break the line, the ends are drawn together into closed rings. Owing to the Bernoulli effect, the higher velocity fluid around the core of the vortex is at a lower pressure than the fluid circulating farther away. Air is injected into the rings via bubbles released from the dolphin's blowhole." The energy of the water vortex is enough to keep the bubbles from rising for a reasonably long period--on the order of 10 seconds. There also seems to be a separate mechanism for producing small rings, which a dolphin can accomplish by a quick flip of its head.
There is little doubt that this is what is occurring. However, understanding the physics should not diminish our appreciation of this spontaneous act of creation by a dolphin mind. These young dolphins have detected, understood, and manipulated a subtle aspect of their environment, for no reason other than play.
Creation of these rings by dolphins isn't new. (far from it--dolphins were probably blowing magnificent silver rings while our anscestors were hanging off tree limbs). It does seem to be a relatively rare behavior, though: it has been seen before only in a specific group of dolphins documented by Diana Reiss and Jan Ostman at Marine World. "The fact that ring-blowing is rare and that we have two babies doing it suggests that one baby learned it from the other", comments Ken Marten. "Whether it was a case of observational learning, or one "taught" the other, we don't know... but it'd sure be interesting to know."
The social situation also seems to
