By replacing school bells in 6,300 French primary schools with the calls of threatened species, WWF turns a daily ritual into a wildlife lesson. For one week in May, recess at more than 6,300 French primary schools starts with a howl, a croak, a song or a click. WWF and Saatchi & Saatchi France have replaced the standard bell with the calls of four threatened species: the boreal lynx on Monday, the whiskered tern on Tuesday, the wolf on Thursday, and the sperm whale to close out the week — turning a sound that sends kids outside into a small, daily lesson on the wildlife they're meant to inherit. The campaign, dubbed L'Appel de la Nature (The Call of Nature), will reach roughly 650,000 children. Teachers get educational kits built around each animal, with blind tests, stories, quizzes and games to fill the gap between hearing a sound at 10 am and knowing who made it.…