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PORTLAND - A great deal is known about the use of sex pheromones in animal species ranging from the gypsy moth to deer, cats and humans, but researchers are now adding the sensory cues of another animal to that list - Asian elephants.

New research outlines how female elephants can detect chemical cues in the urine of other females to determine the phase of their reproductive, or estrus cycle. An elephant is more interested in obtaining this information when she is also in the more fertile, or follicular stage of estrus, the study showed.

The work was conducted by scientists from Oregon State University, Georgia Southern University, and the OGI School of Science and Engineering at the Oregon Health and Science University. It will be published this month in the professional journal Animal Behavior.

The first half of the research was conducted with four female elephants at the Oregon Zoo in Portland.

Using urine periodically collected from one of the females throughout her reproductive cycle, the females were able to discriminate by regular smelling and by responses to their second nose - the "vomeronasal" organ - the reproductive state of their herdmate. In the second half of the research, done at the Ringling Center for Elephant Conservation in Florida, 14 elephants were most interested in follicular urine, this time from an unfamiliar female.

"Female elephant society is extremely tight-knit," said Barbara Slade, a veterinary student at OSU and lead author on the study. "We're not completely sure yet why female elephants want to know when other females in the herd are in estrus. But our study showed that females can obtain this information about changing hormonal status. This may be important in itself as changes in hormonal status may change a female's dominance ranking."

Such information, Slade said, could also tell the females when older male elephants may soon be visiting the herd. Or it could help females of a herd to produce only a small number of offspring at any particular time, since the young elephants have to be guarded by the entire herd.

"To study how elephant pheromones actually function, we must first link behaviors and olfactory responses to secretions or body odors of elephants and then define specific chemicals or mixtures that cause these behaviors," said L.E.L. "Bets" Rasmussen, a research chemist at OHSU's OGI School of Science and Engineering. "This study has taken that first step with female Asian elephants."

It took decades of research to identify the female-to-male sex pheromone in Asian elephants, a landmark discovery Rasmussen made in 1996. "Hopefully, it will not take as long to identify these female-to-female cues," said Bruce A. Schulte, a biologist at Georgia Southern University and third author of this study.

Elephant experts around the world, especially in Asia and Africa, are anxious for any progress in this area, Slade said, as herds come under increasing pressure and any information about their reproductive or other behaviors may be useful in preserving populations. In Southeast Asia, there are only 40,000 or fewer elephants remaining.

"In parts of Southeast Asia right now there's a terrible drought and a lot of wildlife watering holes are drying up," Slade said. "This increases conflicts between humans and wildlife who are foraging for water or food, and we need to find out all we can about the behavior of these animals if we hope to preserve them."

The emerging study of animal pheromones has actually made its greatest strides with insects, Slade said, in research usually done for purposes of insect control. But many animals use these semiochemical cues for regulating sex and other behaviors, such as territorial defense. One pioneering and ongoing study among human females demonstrated human pheromones, in this case causing women in group-living arrangements to synchronize their menstrual periods.

In previous studies, the researchers at OSU, Georgia Southern and the OGI School of Science and Engineering found in Asian elephants an unusual behavior called "flehmen," in which females touch the tip of their trunks to a substance and then bring it to their second nose, the vomeronasal organ in the roof of their mouth. This organ has been found in many vertebrates to play a key role in processing the smell of pheromones.

"It's clear that female elephants, for reasons not determined yet, are extremely interested in the reproductive cycles of other females in the herd," Slade said.

"They've even got a very strange tail-waving procedure they do during another part of their reproductive cycle. Everything we've deciphered about elephants suggests they do things for a reason. Now we need to find out what they're doing with this knowledge about each other's estrus cycle."