Although elephants are well known for the trumpeting calls that they make when angry or disturbed, they are also capable of using ultrasound (sounds above the range of human hearing) and infrasound (sounds below the range of human hearing) to communicate with one another. Researchers have concluded that elephants may be able to hear ultrasonic calls from as far away as 2.5 miles (4 kilometers). In contrast, it is estimated that an infrasonic call by a male elephant could in fact cover an area of 11.6 square miles (30 square kilometers).