#rheiformes

(Sources - 1, 2 )

Our next order of paleognath birds are the Rheiformes, commonly called “rheas”. It contains one living family, Rheidae, and one living genus with two species: the “Greater Rhea” or “American Rhea” (Rhea americana) (image 1) and the “Lesser Rhea” or “Darwin's Rhea” (Rhea pennata) (image 2).

Like most other paleognaths, rheas are large and flightless with long legs and long necks. They have fluffy, tattered-looking plumage that is gray or brown. Their wings are large for a flightless bird and are spread out while running, to act like sails. When in danger, they flee in a zigzag fashion, using one wing after the other, similar to a rudder. Unlike many other birds, they only have three toes. Rheas are mainly herbivorous and prefer broad-leafed plants, but they also eat fruits, seeds, roots, and animals such as insects, small reptiles, and rodents. Living rheas are only from South America and are limited within the continent to Argentina, Bolivia, Brazil, Chile, Paraguay, Peru and Uruguay. They live in open grasslands, the pampas, and chaco woodlands.

During the non-breeding season rheas may form flocks of between 10 and 100 birds, although the Lesser Rhea usually forms smaller flocks. These flocks will feed alongside deer and cattle. During the breeding season, the flocks break up, with males attempting to attract females with a loud, booming call, running short distances, and waving his neck back and forth. Rheas are polygynandrous, with males courting between two and twelve females and females commonly mating with multiple dominant males during the breeding season. After mating, the male builds a nest where each female will lay her eggs. The nest is a simple scrape in the ground, lined with grass and leaves. The male incubates from ten to sixty eggs, and may use a subordinate male to incubate his eggs while he finds another group of females to start a second nest with. The chicks will all hatch together, synchronizing their hatching via whistling within the eggs. While caring for the young, the males will aggressively charge at any perceived threat approaching the chicks, including female rheas and humans. Young rheas eat only insects for their first few days. They reach full adult size in about six months but do not breed until they reach two years of age.

Rheiformes arose in the Eocene, around 40 million years ago, with the living genus Rhea evolving in the Pleistocene.

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Propaganda under the cut:

Lesser Rhea (Rhea pennata)

Rheiformes. This order is made up of rheas, plant-eating flightless birds of South America

Apterygiformes. This order is made up of kiwis, small nocturnal flightless birds of New Zealand. They have hair-like feathers and poor eyesight.

Renowned Rheas

A distant cousin to the ostrich and the emu, rheas or ñandus are a group of birds belonging to the genus Rhea, consisting of the common rhea ( Rhea americana) and the lesser rhea (Rhea pennata). Also included as either a subspecies or a seperate species is the puna rhea ( Rhea tarapacensis). This group is found in the southern half of South America, typically in open grasslands or sparse woodlands.

Like their flightless relatives, rheas are large, flightless birds characterised by a small head, long neck, and long legs. Adults of the common rhea species can reach up to 1.5 m (4 ft 11 in) tall and 27 kg (60 lbs), while the smaller species only reach 1 m (39 in) and 29 kg (63 lbs). All members of the rhea group have dull grey or brown coloration. Males are typically larger than females, although both possess large clawed feet which are used for outrunning or out-kicking predators like cougars (Puma concolor) and pampas cats ((Leopardus colocolo), which often go after nests or chicks.

Rheas are largely herbivorous, and spend most of their days grazing. Their diets consist of grass, cacti, saltbrush, and the occasional small lizard or insect. Outside the breeding season they can be found in flocks of 10-100, with individuals taking turns watching for potential threats while the others graze. During the breeding season, from July to January, males fight each other with their sharp claws and beaks to gain dominance. The victor mates with up to 12 females, each of which produces a clutch of 20-40 eggs each season.

 Once the eggs are laid, the males provide all the care for the offspring. These eggs are laid once every 48 hours, and most are moved to a nest for protection. However, some eggs are left to rot, and the flies they attract serve as food for the brooding males and their chicks. Eggs take about 30 days to hatch, and the young are taken are of for an additional six months. Rhea fathers are extremely territorial, and will become aggressive even towards other females, all while guarding several broods of chicks. Once they reach independence at six months old, chicks join a group of young adults, though they don’t become sexually mature until they’re about two years old. In captivity individuals can live up to 13 years.

Conservation status: The greater rhea is considered Near Threatened by the IUCN, while the lesser rhea is classified as Least Concern. Their main threats are habitat destruction and increased hunting and nest poaching from humans.

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Photos

Dave Curtis via eBird

Konrad Wothe

Lesser Rhea (Rhea pennata)

Lesser rhea (Rhea pennata)