Some was sprinkled around the base of a tree. More was scattered over the floor of the tram garage. But it was just outside one of the veterinary clinics, under a wide overhanging awning, that Michelle Tirhi got really excited. “Look at all that!” she exclaimed, sweeping her eyes around the concrete floor. “And it’s all fresh! We could just scoop up some right now.” Bending down, she picked up a tiny black sliver the size and shape of a rice grain and held it up triumphantly. Bat poop. Or guano, to be precise. Tirhi, the District II wildlife biologist …