Why do dogs keep stopping to urinate, and why do they roll in animal carcasses?

R.S.

Fayetteville, Tenn.

A. Urination serves more than one purpose for dogs.

They use urine to ``scent-mark'' their territories. Because dogs have such a keen sense of smell, urine serves as a potent form of communication.

``It leaves a message saying `I was here' and marks territories to let other dogs know that `this is my territory,' '' says Jacqui Neilson, a veterinarian in the animal behavior service of the Veterinary School at the University of California at Davis. ``It's a behavior they brought with them through domestication.''

Dogs will often urinate in a spot after they have spent some time exploring the scents left there by other dogs. Male dogs, which are known to be more territorial than females, scent-mark more often than females, says Neilson.

Some animals, including beavers, hyenas and some hamsters, have specialized scent glands that produce scented secretions. The animals smear these secretions at strategic locations to mark territories and advertise their presence.

The second part of your question also involves some intriguing aspects of dog behavior. Any dog owner knows that dogs have strong preferences in smell: dead stuff, places other dogs have urinated (like fire hydrants,) feces and other doggies' behinds. Yuck, right?

We think fresh pine needles or roses smell much better, and we often project that human-centered view on our dogs. Says Amy Marder, an animal behavior consultant for Angell Memorial Hospital: ``The things dogs roll in smell bad to human beings, but not to dogs. They smell very interesting to dogs.''

Why do they roll in carcasses and other smelly objects? One theory is that they're trying to camouflage their own scent. This could have been an advantage in their evolutionary past -- when they were hunters and wanted to be able to sneak up on their prey.

But Marder has a different view, based on watching animals gleefully roll in dead and smelly items. ``They look like they really enjoy it. They like getting this scent on their bodies,'' she says. ``It's like they're putting perfume on.''