CHICAGO (Reuters) -- Scientists are learning more about how zoo animals feel and how a toy or a little training can sometimes help cut the endless pacing and other repetitive behaviors that are often assumed to be signs of distress.

Some big cats want a high perch from which to view visitors, polar bears want to scratch for hidden caches of food, and male barn swallows could use a tail extension to appeal to potential mates, according to experts from zoos and universities meeting on Friday at Chicago's Brookfield Zoo.
Visitors who see a cheetah pacing or a polar bear swimming in circles might assume they are stressed by confinement. But they may simply be expending excess energy or soothing themselves, experts said interviews at the symposium.
""We humans swim laps, and people take comfort in walking in circles. As long is it not injuring the animals, and not causing them pain, it may not be a sign of poor welfare,"" said Nadja Wielebnowski of the Chicago Zoological Society.
Wielebnowski measures stress hormones in zoo animals and her work is helping guide efforts to reduce stress when animals are moved, come in close contact with humans or are exposed to noise.
""Some species do absolutely great in zoos -- they get great food, they get it every day, they have great veterinary care. For some species, the zoo trumps the wild,"" said David Shepherdson of the Oregon Zoo in Portland.
But some species, like elephants, large cats, and bears, often do not fare as well.
In a study of polar bears in U.S. zoos, Shepherdson found 50 of 54 bears displayed behavioral symptoms of stress, but they showed no elevated levels of corticosteroids, which are hormones that indicate stress, he said. Shepherdson found about half the animals reduced their repetitive behavior when give some training or playthings that helped them mimic behavior in the wild. For example, polar bears given a plastic barrel tended to crush it just as they would a seal den in the Arctic.
Experts are also discussing whether certain species, like certain types of leopard, do not belong in zoos at all because they prefer to remain out of sight.
""Essentially, we need to go against the knee-jerk human reaction, which is the view that (zoo animals) need companionship, they need a large enclosure, and that they are only interested in the world visually,"" said Vicki Melfi of Whitley Wildlife Conservation Trust, which runs the Paignton Zoo in Britain.
She said animals more sensitive to smell should be accommodated, for instance, by not disinfecting their enclosures frequently so as not to wipe out scent markings. Other animals sensitive to sounds might be offered a dark, quiet corner to retreat to. Wielebnowski suggested zoos might consider exercise equipment for animals to burn off energy.
Wayne Pacelle, president of the Humane Society of the United States, said measuring hormone levels may not tell the story as well as observing listless or repetitive behavior.