Southern Cassowary

The cassowary’s tall casque puzzled scientists for nearly 200 years. Infrared imaging of 20 live southern cassowaries in Australian zoos suggests it works as a thermal radiator that limits heat loss when cold: in hot conditions it lost more heat for its size than the eye, bill, neck, or body, accounting for about 8 percent of the bird’s total heat exchange. The casque is a keratin covering over a porous, blood-vessel-rich core, and it stands roughly 13 to 20 cm (5.1 to 7.9 in) high. Other proposed roles include protecting the head in dense undergrowth and signaling age or dominance, but none is confirmed, and both sexes have one. Hatchlings are born without a casque, and it develops over about 4 to 5 years, alongside the black adult plumage.

Each foot has a dagger-like claw on the inner toe, up to about 12 cm (4.7 in) long, and cassowaries can leap nearly 2 m (6.6 ft) into the air and kick hard. Adults wear stiff, bristly black plumage and can run up to 50 km/h (31 mph). Still, deaths are rare: only two human fatalities have been reported since 1900. A 2003 study of 221 historical attacks found that most involved a bird chasing or charging, and about 75 percent of attacks on humans involved birds that people had fed. Just one death occurred among the 150 attacks on humans in that study. Feeding draws cassowaries closer to people and raises the risk of encounters. In the wild they are solitary and wary, and most trouble starts when people feed them.

Cassowaries eat fruit from more than 238 rainforest plant species and pass the seeds intact in their droppings, often more than 1 km (0.6 mi) from the parent tree. They are the only animal able to disperse the seeds of over 70 rainforest trees whose fruit is too large for other animals to carry, and large-seeded species such as black palm and Davidson’s plum depend on them. In a study of one rare tree, seeds that passed through a cassowary were more likely to sprout than seeds that fell naturally. The droppings often hold hundreds or thousands of seeds and also act as fertilizer. A cassowary can eat up to 5 kg (11 lb) of fruit a day, and its digestive system safely handles some fruits that are toxic to other animals.

Southern cassowaries are solitary and wary, living in dense, remote rainforest. Home ranges run roughly 0.52 to 2.35 sq km (0.2 to 0.9 sq mi), varying with season and food supply. In the Daintree, adult males typically use about 100 to 150 hectares (247 to 371 acres) and females 150 to 250 or more (371 to 618 acres), moving between several male territories during breeding. Adults mostly meet during the breeding season, roughly May to November. Juveniles leave their father’s territory at about 9 to 12 months and must find space of their own. Otherwise adults keep apart. When two males meet, they posture and rumble until one leaves, and a female can drive off a male by stretching and staring. Deep booming calls carry through the forest, allowing contact without close encounters.

Cassowaries reverse the usual bird parenting roles. Courtship and mating in the Daintree take place in May and June. Females are polyandrous: a female lays 3 to 5 large green eggs in a ground scrape for one male, then leaves and lays further clutches for other males, mating with 2 to 3 males in a season. Each male incubates his eggs alone for about 50 days, often without leaving the nest to eat or drink. He then raises the striped chicks entirely by himself. They walk and follow him within hours of hatching. He keeps them for roughly 9 to 12 months, with some sources giving 8 to 18, before growing more aggressive and driving them off to find their own range. The casque and adult plumage take about 4 to 5 years to develop.

Cassowaries produce the lowest known bird call, a deep boom at the edge of human hearing. Territorial roars measured at about 23 Hz were up to 40 decibels louder than forest background noise, and the sound carries long distances through dense rainforest. Males boom in series to attract females during the breeding season, and the call is described as made by resonating air in the chest cavity. These roars also help each bird defend its own range against others. Cassowaries also hiss and rumble, and chicks make high-pitched whistles and chirps to call their father. The casque may help detect low-frequency sound, though this is unconfirmed. For a species that spends most of its life alone, this long-range sound lets neighbors, mates, and rivals stay aware of one another.