Rhea (bird)

The genus contains two extant species and eight subspecies, although one subspecies is disputed:[7]

Image	Scientific name	Common name	Subspecies	Distribution
	Rhea americana (Linnaeus, 1758)	Greater rhea	R. a. americana (Linnaeus, 1758), live in the cerrados (bushlands) and caatinga of central and eastern Brazil. R. a. intermedia Rothschild & Chubb 1914, intermediate rhea of southeastern Brazil in Rio Grande do Sul and Uruguay R. a. nobilis Brodkorb 1939, eastern Paraguay, east of Rio Paraguay R. a. araneipes Brodkorb 1938, chaco of Paraguay to Bolivia and Mato Grosso in Brazil R. a. albescens Lynch & Holmberg 1878, plains of Argentina south of Rio Negro	Argentina, Bolivia, Brazil, Paraguay and Uruguay
	Rhea pennata d'Orbigny 1834	Darwin's rhea or lesser rhea	R. p. garleppi (Chubb 1913), puna/Garlepp's rhea of southeastern Peru, southwestern Bolivia and northwestern Argentina. It is included in R. tarapacensis by The International Union for Conservation of Nature (IUCN). R. p. pennata d'Orbigny 1834, Darwin's lesser rhea of Patagonian steppes in southern Argentina and southern Chile	Altiplano and Patagonia in South America
	Rhea tarapacensis Chubb 1913	Puna rhea	No subspecies, but some consider it as a subspecies of the lesser rhea. The IUCN lists it as a third species.[8]	Tarapacá Rhea of northern Chile from Atacama to Tarapacá

Rhea pennata was not always in the genus Rhea. In 2008, the SACC, the last holdout, approved the merging of the genera, Rhea and Pterocnemia on August 7, 2008. This merging of genera leaves only the genus Rhea.[9] A former fourth species of rhea, Rhea nana, was described by Lydekker in 1894 based on a single egg found in Patagonia,[10] but today no major authorities consider it valid.

• †R. anchorenense (Ameghino & Rusconi 1932) [Rhea americana anchorenense Amcghino & Rusconi 1932]
• †R. fossilis (Moreno & Mercerat 1891) [Pterocnemia fossilis (Moreno & Mercerat 1891); Rhea pampeana (Moreno & Mercerat 1891)]
• †R. mesopotamica (Agnolín & Noriega 2012) [Pterocnemia mesopotamica Agnolín & Noriega 2012]
• †R. subpampeana Moreno & Mercerat 1891

A small population of rheas has emerged in Mecklenburg-Western Pomerania, northeastern Germany, after several couples escaped from an exotic meat farm near Lübeck in the late 1990s. Contrary to expectations, the large birds adapted well to conditions in the German countryside.[16] A monitoring system has been in place since 2008.[17] By 2014, there was already a population of well over 100 birds in an area of 150 square kilometres (58 sq mi) between the river Wakenitz and the A20 motorway, slowly expanding eastward.[18]

Feral greater rhea flock in Germany

The population grew steadily for several years. By autumn 2018 their numbers had greatly increased to about 600. As such, local farmers claim increasing damage to their fields, and some biologists say the rheas pose a growing risk to local wildlife. Still protected by German natural conservation law, a local discussion has begun regarding how to handle the situation. Eventually, Mecklenburg-Western Pomerania's government allowed limited hunting of the birds, explicitly to just reduce the population's growth and not to wipe them out. At this point, it was generally agreed that the rheas should be allowed to stay in the region. By spring 2021, just 247 rheas were counted; this development was attributed to both the hunting as well as the increased caution of the animals. Several had begun to avoid humans more than previously, and retreated into the woods.[19][20] Some members of this rhea population have also expanded into other areas; at least twice individual rheas who probably originated in Mecklenburg-Western Pomerania were sighted in Brandenburg's High Fläming Nature Park, over 200 kilometres (120 mi) from their usual range.[21]

There also appears to be a small population of wild rheas in the United Kingdom. In March 2021, a group of about 20 rheas were reported to be running free on a residential estate in Hertfordshire. Local police were unable to identify any owner, so the assumption was that they were wild birds. Once caught, authorities intend to place them in a suitable nature reserve to allow them to develop as a colony.[22]

Rheas tend to be silent birds, with the exception being when they are chicks or when the male is seeking a mate. During breeding season, the male will attempt to attract females by calling. This call is a loud booming noise. While calling like this, they will lift the front of their body, ruffle their plumage, all while keeping their neck stiff. They will then extend and raise their wings, and run short distances, alternating with their wings. He may then single out a female and walk alongside or in front of her with a lowered head and spread wings. If the female notices him, then he will wave his neck back and forth in a figure eight. Finally, a female may offer herself and copulation will commence.[11]

During the non-breeding season they may form flocks of between 20 and 25 birds,[23] although the lesser rhea forms smaller flocks than this. When in danger they flee in a zigzag course, using first one wing then the other, similar to a rudder. During breeding season the flocks break up.[11]

For the most part, rheas are herbivorous and prefer broad-leafed plants but they also eat fruits, seeds and roots, as well as insects such as grasshoppers and small reptiles and rodents.[11] Young rheas generally eat only insects for the first few days. Outside of the breeding season they gather in flocks and feed with deer and cattle.[23]

Rheas are polygamous, with males courting between two and twelve females. After mating, the male builds a nest, in which each female lays her eggs in turn. The nest consists of a simple scrape in the ground, lined with grass and leaves.[13] The male incubates from ten to sixty eggs. The male will use a decoy system and place some eggs outside the nest and sacrifice these to predators, so that they do not attempt to get inside the nest. The male may use another subordinate male to incubate his eggs, while he finds another harem to start a second nest.[11] The chicks hatch within 36 hours of each other. Right before hatching, the chicks begin to whistle.[24] The females, meanwhile, may move on and mate with other males. While caring for the young, the males will charge at any perceived threat that approach the chicks including female rheas and humans. The young reach full adult size in about six months but do not breed until they reach two years of age.[13]