It is possible stingrays just jump for joy

'Why do stingrays throw themselves high in the air?" a friend asked by e-mail.

"Would this be because they are being chased, or perhaps to throw parasites off their bodies? I wonder what ideas you have."

I've read some theories about this, but we humans never know for sure why animals behave the way they do. The animals know but they aren't telling. For us it's all guesswork.

I assumed rays jumped for the same reason most fish jump: to avoid being eaten. Sharks prey on rays, and a vertical leap from the water might confuse a shark.

Julie's other guess could be true, too. Remoras (also called suckerfish) often stick to rays for free rides, and a good jump could dislodge the pest.

And here's an observation worth pondering: People have seen both eagle and manta rays delivering baby rays while in the air. This behavior hasn't been seen in stingrays, however, because stingrays don't jump.

Most people use the term stingray to mean all rays, but researchers classify these odd-shaped fish into three distinct families: stingrays, eagle rays and manta rays.

Stingrays have roundish bodies and would rather hide than jump. These disclike fish, about 4 feet wide in Hawaii, wiggle over the ocean floor looking for snails, worms and crustaceans. When it's time to rest, stingrays nestle into the sand, sometimes covering themselves until only their eyes show.

It's when stingrays lie buried like this that human waders can get a nasty surprise. Stepping on a stingray causes the alarmed animal to swing its tail toward the offender, puncturing the skin with its poisonous stinger.

Stingrays (and their stings) are rare in Hawaii.

Eagle and manta rays resemble kites rather than discs, and their pectoral fins flap like wings. Like stingrays, eagle rays also eat shelled animals from the ocean floor, but unlike stingrays, they don't rest there. Instead, eagle rays cruise well off the bottom, and sometimes at the surface, perhaps looking for concentrations of shellfish.

Eagle rays often gather in small groups and "fly" in formation. Hawaii's one species (there are 10) grows to about 6 feet wide.

Each eagle ray has a stinger at the base of its tail, but stings from eagle rays are rare. They're always on the move, and it's hard to get close to them.

But accidents happen. In March, in Florida, an airborne eagle ray collided with a woman traveling 25 mph in a boat. "Stingray attack kills woman," shouted some headlines. But it was no attack. The tragedy was a case of being in the wrong place at the wrong time. Both the ray and the woman died from the impact.

The largest rays are mantas, weighing up to 3,000 pounds with a width of more than 20 feet. Manta rays tangled in harpoon or anchor lines have towed small boats around for hours.

They look scary but manta rays are harmless. These plankton eaters have no stingers.

All three kinds of rays produce three or four eggs that stay in the mother's uterus. After the thin shells dissolve, the mother secretes a nutritious fluid that the developing young take up through skin and stomach.

No one knows for sure if eagle and manta rays leap to avoid predators, lose parasites or ease labor pains. It's possible, though, that none of the above apply. Maybe rays jump because it's fun.

Marine science writer Susan Scott can be reached at www.susanscott.net.