Grey-Crowned Crane

Grey crowned cranes are one of only two crane species that roost in trees. The other is their close relative, the black crowned crane. Both have a long hind toe that can grasp branches, a trait thought to be an ancestral feature among cranes. At night, grey crowned cranes can rest and sleep in trees, which helps them avoid many ground predators. Roosting habits vary, though. Outside the breeding season, non-breeding birds often roost together in trees or even on overhead utility structures. Breeding pairs, by contrast, may stay on the ground in wetlands near their nest, while parents with chicks roost in nearby trees. The grasping toe is their key adaptation for perching.

Grey crowned cranes often forage alongside grazing animals. As cattle and wild antelopes and gazelles walk through grassland, they disturb insects and other small creatures, and the cranes follow close behind to catch what they flush out, much as cattle egrets do. Cranes also stamp their feet as they walk, startling insects out of the grass so they can be snapped up quickly. They spend much of the day searching for food. They also make use of disturbances made by other species, and forage in newly plowed fields. Their catches include insects, lizards, frogs, and worms. Foraging near large livestock is thought to help deter predators, giving the birds a safety benefit along with an easy meal.

Grey crowned cranes are omnivores with a wide-ranging diet. They eat grass and sedge seeds, grain, insects, worms, lizards, frogs, snakes, crabs, small fish, and even the eggs of aquatic animals. This flexibility lets them live in natural wetlands and on human-modified farmland alike. In farm country they forage in pastures and newly planted fields, and will eat maize, picking kernels directly from the cob. Damage to maize is greatest in the first two to three weeks after planting, when seeds and seedlings are easy to pull up. Their adaptability has not shielded them from habitat loss. Wetland drainage, overgrazing, and pesticide pollution threaten them, and the species is now listed as Endangered.

Grey crowned cranes are famous for their dances, which involve calling with the throat pouch inflated, head bobbing, bowing, wing spreading, and a series of jumps. Both sexes dance, and either partner can start or end a display. The dances play a central role in courtship, but they are not limited to the breeding season and can happen at any time of year. Immature birds join the adults. Grey crowned cranes appear to mate for life, and mutual preening may help maintain pair bonds outside the breeding season. Large groups also gather for a wedding-like ceremony when young birds pair off. The crane is also Uganda’s national bird, appearing on the country’s flag and coat of arms.

Grey crowned cranes are social birds that flock together, especially in winter and into spring when they are not breeding. Flocks of 30 to 150 birds are not uncommon. Non-breeding birds may also roost together at night, in trees or on overhead utility structures. Young birds join groups of other juveniles after fledging. During the breeding season, pairs become very territorial around their nest sites, with one estimate putting territory size at about 0.86 to 3.88 km² (0.3 to 1.5 sq mi). The cranes do not migrate, but they move with food and water, and those movements can be extensive in drier regions. This flexible social structure lets them gain the safety and foraging benefits of a flock while still protecting the space they need to raise chicks.

Both partners help build the nest, a large platform of grass and other plants set in tall wetland vegetation in or near standing water. The tall cover hides the sitting bird while leaving its head visible. Both parents share incubation of the clutch of two to five eggs, which hatch after 28 to 31 days. Chicks are precocial, able to run soon after hatching and even swim at about 12 hours old. Parents hide them in tall marsh grass, and both keep caring for the young until fledging at 56 to 100 days. Pairs are very territorial around the nest site. Young birds eventually leave their parents and start their own families, reaching maturity at about three years.