Kori Bustard

It is generally cited as the heaviest bird that regularly flies under its own power, with large males weighing up to around 19 kilograms, occasionally reported slightly higher. A handful of other very large flying birds, such as the great bustard of Eurasia and the largest swans and condors, approach or occasionally exceed typical kori bustard weights in exceptional individuals, so the exact ranking can shift depending on which record specimens are compared, but the kori bustard is consistently near the top of any such list and is the standard example given for the heaviest flying bird. Ostriches and emus are heavier still but are flightless.

With difficulty and reluctance. A kori bustard strongly prefers walking to flying and does most of its foraging entirely on foot across open grassland, only taking to the air when necessary, such as to escape a serious threat or cross an obstacle. Taking off requires a running start of several strides while beating its large wings heavily to generate enough lift, similar in principle to how a heavily loaded aircraft needs a long runway, and once airborne it flies with slow, powerful wingbeats interspersed with gliding on its broad wings rather than sustained flapping flight, conserving energy wherever possible.

It is one of the most striking displays among ground-dwelling birds. A male gathers at a traditional display area and, to attract females, inflates a large sac of loose skin on his throat and neck until it hangs down almost to the ground, forming a big white balloon-like structure that contrasts with his cryptic brown body plumage. At the same time he raises his tail up and forward over his back, droops both wings so their tips trail along the ground, retracts his neck, and struts back and forth while producing a deep, resonant booming call, repeating the whole sequence for extended periods. Several males may display within sight of each other, and females move between them to assess and choose a mate before departing to nest alone.

Several pressures compound for a large, ground-dwelling bird with a slow reproductive rate, since a female raises only one or two chicks at a time with no help from the male and does not breed every year. Its open grassland and savanna habitat is increasingly converted to agriculture or degraded by overgrazing, it collides fatally with the power lines and fences that increasingly crisscross its range because its size and flight style make it a poor flier around obstacles, and it is hunted for meat and sometimes for its plumes and reputed traditional medicinal uses across parts of its range. Because populations are large-bodied and slow to recover, even moderate additional adult mortality can outpace reproduction, which is reflected in its Near Threatened status and ongoing decline in several countries.