Since the ratio between flamingos and chachalacas is 2:1, we see that the ratio of flamingos to chachalacas to parrots to herons is 10:5:7:3. The sum of these numbers is 25, so every 'ratio number' gets 375/25 = 15 animals. So the number of chachalacas is 15 * 5 = 75.
