While giraffes are usually found in groups, the composition of these groups tends to be open and ever-changing.[62] They have few strong social bonds, and aggregations usually change members every few hours. For research purposes, a "group" has been defined as "a collection of individuals that are less than a kilometre apart and moving in the same general direction."[63] The number of giraffes in a group can range up to 32 individuals.[62] The most stable giraffe groups are those made of mothers and their young,[63] which can last weeks or months.[64] Social cohesion in these groups is maintained by the bonds formed between calves.[10]:330[63] Mixed-sex groups made of adult females and young males are also known to occur.[63] Subadult males are particularly social and will engage in playfights. However, as they get older males become more solitary.[64] Giraffes are not territorial,[15] but they have home ranges.[25] Male giraffes occasionally wander far from areas that they normally frequent.[10]:329
Reproduction is broadly polygamous: a few older males mate with the fertile females. Male giraffes assess female fertility by tasting the female's urine to detect oestrus, in a multi-step process known as the flehmen response.[63][64] Males prefer young adult females over juveniles and older adults.[63] Once an oestrous female is detected, the male will attempt to court her. When courting, dominant males will keep subordinate ones at bay.[64] During copulation, the male stands on his hind legs with his head held up and his front legs resting on the female's sides.[25]
Although generally quiet and non-vocal, giraffes have been heard to communicate using various sounds. During courtship, males emit loud coughs.[25] Females call their young by bellowing. Calves will emit snorts, bleats, mooing and mewing sounds. Giraffes also snore, hiss, moan, grunt and make flute-like sounds,[25][65] and they communicate over long distances using infrasound.[66] During nighttime, giraffes appear to hum to each other above the infrasound range for purposes which are unclear.[65]