 One specific type of echolocation, narrow-band high frequency (NBHF) clicks, evolved at least four times in groups of odontocetes, including the pygmy sperm whale (Kogiidae) and porpoise (Phocoenidae) families, "Pontoporia blainvillei", the genus "Cephalorhynchus", and part of the genus "Lagenorhynchus".These high frequency clicks likely evolved as adaptation of predator avoidance, as they inhabit areas that have many killer whales and the signals are inaudible to killer whales due to the absence of energy below 100 kHz.Another reason for variation in echolocation is habitat.