their heads at each other, horns first, a behavior known as "necking". A subordinate okapi signals submission by placing its head and neck on the ground. Giraffes are sociable, whereas okapis live mainly solitary lives. Giraffes temporarily form herds of up to 20 individuals; these herds can be mixed or uniform groups of males and females, young and adults. Okapis are normally seen in mother-offspring pairs, although they occasionally gather around a prime food source. Giraffe are not territorial, but have ranges that can dramatically vary between — — depending on food availability, whereas okapis have individual ranges about in size. Giraffes and okapis are normally silent, but both have a range of vocalizations, including coughing, snorting, moaning, hissing, and whistling. Giraffes have been suggested to be able to communicate using infrasonic sounds like elephants and blue whales. Notes References Mammal families Extant Burdigalian first appearances Taxa named by John Edward Gray