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The rheas ( ), also known as ñandus ( ) or South American ostriches, are large
ratite A ratite () is any of a diverse group of flightless, large, long-necked, and long-legged birds of the infraclass Palaeognathae. Kiwi, the exception, are much smaller and shorter-legged and are the only nocturnal extant ratites. The systematics ...
s (
flightless bird Flightless birds are birds that through evolution lost the ability to fly. There are over 60 extant species, including the well known ratites (ostriches, emu, cassowaries, rheas, and kiwi) and penguins. The smallest flightless bird is the ...
s without a
keel The keel is the bottom-most longitudinal structural element on a vessel. On some sailboats, it may have a hydrodynamic and counterbalancing purpose, as well. As the laying down of the keel is the initial step in the construction of a ship, in Br ...
on their sternum bone) in the order Rheiformes, native to
South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the sou ...
, distantly related to the
ostrich Ostriches are large flightless birds of the genus ''Struthio'' in the order Struthioniformes, part of the infra-class Palaeognathae, a diverse group of flightless birds also known as ratites that includes the emus, rheas, and kiwis. There ...
and emu. Most taxonomic authorities recognize two extant species: the greater or American rhea (''Rhea americana''), and the lesser or Darwin's rhea (''Rhea pennata''). The
International Union for Conservation of Nature The International Union for Conservation of Nature (IUCN; officially International Union for Conservation of Nature and Natural Resources) is an international organization working in the field of nature conservation and sustainable use of natu ...
(IUCN) classifies the
puna rhea Darwin's rhea or the lesser rhea (''Rhea pennata'') is a large flightless bird, the smaller of the two extant species of rheas. It is found in the Altiplano and Patagonia in South America. Description The lesser rhea stands at tall. Leng ...
as another species instead of a subspecies of the
lesser rhea Darwin's rhea or the lesser rhea (''Rhea pennata'') is a large flightless bird, the smaller of the two extant species of rheas. It is found in the Altiplano and Patagonia in South America. Description The lesser rhea stands at tall. Leng ...
. The IUCN currently rates the greater and puna rheas as near-threatened in their native ranges, while Darwin's rhea is of least concern. In addition, a feral population of the greater rhea in Germany appears to be growing, though control efforts are underway, and seem to be succeeding in controlling the birds' population growth.


Etymology

The name "rhea" was used in 1752 by Paul Möhring and adopted as the
English English usually refers to: * English language * English people English may also refer to: Peoples, culture, and language * ''English'', an adjective for something of, from, or related to England ** English national ...
common name. Möhring named the rhea after the Greek Titan Rhea, whose
Ancient Greek Ancient Greek includes the forms of the Greek language used in ancient Greece and the ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Dark Ages (), the Archaic pe ...
name () is thought to come from "ground". This was fitting with the rhea being a flightless ground bird. Depending on the South American region, the rhea is known locally as ( Guaraní, meaning big spider, most probably in relation to their habit of opening and lowering alternate wings when they run), ( Portuguese), ( Aymara and Quechua), or (
Mapudungun Mapuche (, Mapuche & Spanish: , or Mapudungun; from ' 'land' and ' 'speak, speech') is an Araucanian language related to Huilliche spoken in south-central Chile and west-central Argentina by the Mapuche people (from ''mapu'' 'land' and ''che ...
). is the common name in many European languages and may sometimes also be heard in English.


Taxonomy and systematics

The
genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...
''Rhea'' was introduced by the French zoologist
Mathurin Jacques Brisson Mathurin Jacques Brisson (; 30 April 1723 – 23 June 1806) was a French zoologist and natural philosopher. Brisson was born at Fontenay-le-Comte. The earlier part of his life was spent in the pursuit of natural history; his published wo ...
in 1760 with the
greater rhea The greater rhea (''Rhea americana'') is a species of flightless bird native to eastern South America. Other names for the greater rhea include the grey, common, or American rhea; ema (Portuguese); or ñandú ( Guaraní and Spanish). One of two ...
(''Rhea americana'') as the
type species In zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological type specim ...
.


Extant species

The genus contains two extant species and eight subspecies, although one subspecies is disputed: ''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''. A former fourth species of rhea, ''Rhea nana'', was described by
Lydekker Richard Lydekker (; 25 July 1849 – 16 April 1915) was an English naturalist, geologist and writer of numerous books on natural history. Biography Richard Lydekker was born at Tavistock Square in London. His father was Gerard Wolfe Lydekker, ...
in 1894 based on a single egg found in
Patagonia Patagonia () refers to a geographical region that encompasses the southern end of South America, governed by Argentina and Chile. The region comprises the southern section of the Andes Mountains with lakes, fjords, temperate rainforests, and g ...
, but today no major authorities consider it valid.


Fossils

* †'' 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)] * †''Rhea mesopotamica, R. mesopotamica'' (Agnolín & Noriega 2012) [''Pterocnemia mesopotamica'' Agnolín & Noriega 2012] * †''Rhea subpampeana, R. subpampeana'' Moreno & Mercerat 1891


Description

Rheas are large,
flightless bird Flightless birds are birds that through evolution lost the ability to fly. There are over 60 extant species, including the well known ratites (ostriches, emu, cassowaries, rheas, and kiwi) and penguins. The smallest flightless bird is the ...
s with grey-brown
plumage Plumage ( "feather") is a layer of feathers that covers a bird and the pattern, colour, and arrangement of those feathers. The pattern and colours of plumage differ between species and subspecies and may vary with age classes. Within species, ...
, long legs and long necks, similar to an
ostrich Ostriches are large flightless birds of the genus ''Struthio'' in the order Struthioniformes, part of the infra-class Palaeognathae, a diverse group of flightless birds also known as ratites that includes the emus, rheas, and kiwis. There ...
. Large males of ''R. americana'' can reach tall at the head, at the back and can weigh up to . The lesser rhea is smaller, with a height of . Their wings are large for a flightless bird () and are spread while
running Running is a method of terrestrial locomotion allowing humans and other animals to move rapidly on foot. Running is a type of gait characterized by an aerial phase in which all feet are above the ground (though there are exceptions). This i ...
, to act like
sail A sail is a tensile structure—which is made from fabric or other membrane materials—that uses wind power to propel sailing craft, including sailing ships, sailboats, windsurfers, ice boats, and even sail-powered land vehicles. Sails ma ...
s. Unlike most birds, rheas have only three toes. Their tarsus has 18 to 22 horizontal plates on the front of it. They also store
urine Urine is a liquid by-product of metabolism in humans and in many other animals. Urine flows from the kidneys through the ureters to the urinary bladder. Urination results in urine being excreted from the body through the urethra. Cellul ...
separately in an expansion of the
cloaca In animal anatomy, a cloaca ( ), plural cloacae ( or ), is the posterior orifice that serves as the only opening for the digestive, reproductive, and urinary tracts (if present) of many vertebrate animals. All amphibians, reptiles and birds, ...
.


Distribution and habitat

Rheas are from
South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the sou ...
only and are limited within the continent to
Argentina Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country in the southern half of South America. Argentina covers an area of , making it the List of South American countries by area, second-largest ...
,
Bolivia , image_flag = Bandera de Bolivia (Estado).svg , flag_alt = Horizontal tricolor (red, yellow, and green from top to bottom) with the coat of arms of Bolivia in the center , flag_alt2 = 7 × 7 square p ...
,
Brazil Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the largest country in both South America and Latin America. At and with over 217 million people, Brazil is the world's fifth-largest country by area ...
,
Chile Chile, officially the Republic of Chile, is a country in the western part of South America. It is the southernmost country in the world, and the closest to Antarctica, occupying a long and narrow strip of land between the Andes to the eas ...
,
Paraguay Paraguay (; ), officially the Republic of Paraguay ( es, República del Paraguay, links=no; gn, Tavakuairetã Paraguái, links=si), is a landlocked country in South America. It is bordered by Argentina to the south and southwest, Brazil to t ...
,
Peru , image_flag = Flag of Peru.svg , image_coat = Escudo nacional del Perú.svg , other_symbol = Great Seal of the State , other_symbol_type = National seal , national_motto = "Firm and Happy f ...
, and
Uruguay Uruguay (; ), officially the Oriental Republic of Uruguay ( es, República Oriental del Uruguay), is a country in South America. It shares borders with Argentina to its west and southwest and Brazil to its north and northeast; while bordering ...
. They are grassland birds and both species prefer open land. The greater rheas live in open grasslands,
pampa The Pampas (from the qu, pampa, meaning "plain") are fertile South American low grasslands that cover more than and include the Argentine provinces of Buenos Aires, La Pampa, Santa Fe, Entre Ríos, and Córdoba; all of Uruguay; and Brazi ...
s, and chaco woodlands. They prefer to breed near water and prefer lowlands, seldom going above . On the other hand, the lesser rhea will inhabit most
shrubland Shrubland, scrubland, scrub, brush, or bush is a plant community characterized by vegetation dominated by shrubs, often also including grasses, herbs, and geophytes. Shrubland may either occur naturally or be the result of human activity. It ...
, grassland, even desert salt puna up to .


Feral populations in Europe

A small population of rheas has emerged in
Mecklenburg-Western Pomerania Mecklenburg-Vorpommern (MV; ; nds, Mäkelborg-Vörpommern), also known by its anglicized name Mecklenburg–Western Pomerania, is a state in the north-east of Germany. Of the country's sixteen states, Mecklenburg-Vorpommern ranks 14th in po ...
, northeastern
Germany Germany,, officially the Federal Republic of Germany, is a country in Central Europe. It is the second most populous country in Europe after Russia, and the most populous member state of the European Union. Germany is situated betwee ...
, after several couples escaped from an exotic meat farm near
Lübeck Lübeck (; Low German also ), officially the Hanseatic City of Lübeck (german: Hansestadt Lübeck), is a city in Northern Germany. With around 217,000 inhabitants, Lübeck is the second-largest city on the German Baltic coast and in the state ...
in the late 1990s. Contrary to expectations, the large birds adapted well to conditions in the German countryside. A monitoring system has been in place since 2008. By 2014, there was already a population of well over 100 birds in an area of between the river
Wakenitz The Wakenitz is a river in southeastern Schleswig-Holstein and at the border to Mecklenburg-Vorpommern. The Wakenitz's source is the Ratzeburger See in Ratzeburg. It is about long and drains into the Trave in Lübeck. The majority of its eas ...
and the A20 motorway, slowly expanding eastward. 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. 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 Brandenburg (; nds, Brannenborg; dsb, Bramborska ) is a state in the northeast of Germany bordering the states of Mecklenburg-Vorpommern, Lower Saxony, Saxony-Anhalt, and Saxony, as well as the country of Poland. With an area of 29,480 squ ...
's
High Fläming Nature Park High Fläming Nature Park (german: Naturpark Hoher Fläming) is an 827 km2 nature park in Potsdam-Mittelmark district in the German state Brandenburg. It is the third largest of 11 nature parks in the state of Brandenburg. In 1997, it was dec ...
, over from their usual range. There also appears to be a small population of wild rheas in the
United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the continental mainland. It comprises England, Scotland, Wales and ...
. In March 2021, a group of about 20 rheas were reported be running free on a residential estate in
Hertfordshire Hertfordshire ( or ; often abbreviated Herts) is one of the home counties in southern England. It borders Bedfordshire and Cambridgeshire to the north, Essex to the east, Greater London to the south, and Buckinghamshire to the west. For gov ...
. 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.


Behavior


Individual and flocking

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. During the non-breeding season they may form flocks of between 20 and 25 birds, although the lesser rhea forms smaller flocks than this. When in danger they flee in a
zig-zag A zigzag is a pattern made up of small corners at variable angles, though constant within the zigzag, tracing a path between two parallel lines; it can be described as both jagged and fairly regular. In geometry, this pattern is described as a ...
course, using first one wing then the other, similar to a rudder. During breeding season the flocks break up.


Diet

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. 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.


Reproduction

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. 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. The chicks hatch within 36 hours of each other. Right before hatching, the chicks begin to whistle. 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.


Status and conservation

The numbers of both the greater and puna rhea are decreasing as their habitats are shrinking. Both are considered
near threatened A near-threatened species is a species which has been categorized as "Near Threatened" (NT) by the International Union for Conservation of Nature as that may be vulnerable to endangerment in the near future, but it does not currently qualify fo ...
by the IUCN. The IUCN also states that they are both approaching vulnerable status. The lesser rhea is classified as
least concern A least-concern species is a species that has been categorized by the International Union for Conservation of Nature (IUCN) as evaluated as not being a focus of species conservation because the specific species is still plentiful in the wild. ...
.


Human interaction

Rheas have many uses in South America. Feathers are used for feather dusters, skins are used for cloaks or leather, and their meat is a staple to many people.
Gaucho A gaucho () or gaúcho () is a skilled horseman, reputed to be brave and unruly. The figure of the gaucho is a folk symbol of Argentina, Uruguay, Rio Grande do Sul in Brazil, and the south of Chilean Patagonia. Gauchos became greatly admired and ...
s traditionally hunt rheas on horseback, throwing '' bolas'' or ''boleadoras''—a throwing device consisting of three balls joined by rope—at their legs, which immobilises the bird. The rhea is pictured on Argentina's 1 Centavo coin minted in 1987, and on the Uruguayan 5 peso coin.


Notes


References


External links


Rhea videos
on the Internet Bird Collection * {{Authority control Rheidae Ratites Domesticated birds Flightless birds Higher-level bird taxa restricted to the Neotropics Bird genera Birds of South America Extant Late Pleistocene first appearances Taxa named by Mathurin Jacques Brisson