RIO DE JANEIRO - High above this Brazilian city, in a jungle blanketing a mountain, the turtles were out and the scene was hopeful. Scientists were reintroducing 15 mud-caked tortoises to this urban forest where they had once been plentiful. Children were running around. People were oohing and aahing. A stern-looking security guard briefly appeared to smile. But not government biologist Katyucha Silva.