Chicago: 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 to 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