Koalas are perceived as quiet, solitary animals that spend their days sleeping in eucalyptus trees, but this overlooks their complex social interactions. They possess a varied and sophisticated communication system used to navigate their social world, attract mates, and defend their territory. These methods allow them to interact over both long and short distances in the dense forests they inhabit.
Vocalizations
A striking form of koala communication is the male’s bellow, a sound disproportionately deep for an animal of its size. This vocalization is a series of low-frequency, snoring-like inhalations followed by resonant, belching exhalations. These powerful calls travel far through the forest and are used during the breeding season to attract females and intimidate potential male rivals, advertising the male’s presence and dominance.
This sound is made possible by unique anatomical features. Koalas have a larynx positioned low in their vocal tract, which can be pulled even further down. In addition to standard vocal folds in the larynx, they possess extra folds of tissue in their soft palate, known as velar vocal folds. This structure allows them to create low-pitched sounds that exaggerate their body size, a trait females find attractive when selecting a mate.
While the male bellow is the most prominent sound, koalas produce a range of other vocalizations. Females also bellow, though their calls are softer. Both sexes emit snarls, wails, and screams when threatened or in distress. Young koalas, or joeys, make soft clicking or squeaking sounds to communicate with their mothers, while older joeys might squawk when upset. A cry that sounds like a human baby screaming is a signal of fear or severe stress among all koalas.
Scent Marking
Beyond sound, koalas rely on chemical signals to communicate with one another. Adult male koalas have a prominent scent gland in the center of their chest, which secretes an oily, odorous substance. They use this gland to mark their territory by rubbing their chests against tree trunks. This action deposits a unique chemical signature that serves as a long-lasting message to other koalas.
This scent-marking behavior is a way for males to declare their social status, physical presence, and reproductive readiness. The chemical composition of the secretion is complex, containing around 40 different compounds that can vary with the animal’s age and season. Other koalas, both male and female, will sniff the base of a tree to interpret these olfactory cues. The scent can linger for a significant time, as some home ranges remain vacant for up to a year after an individual’s death until the scent fades.
The act of scent marking is closely tied to a male’s social standing and reproductive cycle. It becomes more frequent during the breeding season, performed by dominant males to establish their territories near breeding females. Younger males wait until they are larger to challenge these established scent marks. This communication allows koalas to understand the social landscape and avoid unnecessary physical confrontations.
Physical Cues and Body Language
At closer ranges, koalas use subtle physical cues and body language to communicate. These visual signals are important during direct interactions, such as disputes over territory or during courtship. An individual’s posture can indicate its mood; for example, agitated or aggressive behavior can signal a warning to another koala to keep its distance. Ear movements are another meaningful form of communication.
This form of interaction is most apparent between a mother and her joey. Mothers use gentle nuzzles and soft cuffs to guide, reassure, or discipline their young. These tactile communications strengthen the bond between them and help the joey learn essential behaviors. Body language requires close proximity and provides immediate feedback during social encounters.