Struthioniformes

cassowaries, emus, kiwis, ostriches, and rheas

(Also: ratites)

Features
By Ellie Bollich

Diversity

Order Struthioniformes includes all of the flightless birds, also known as ratites due to their raft-like sternum that lacks a keel. The order is comprised of five extant families and one extinct family. The five families are Aptergyidae (kiwis), Casuariidae (cassowaries), Dromaiidae (emus), Rheidae (rheas), and Struthionidae (ostriches). The singular extinct family is Dinornithidae (moas), although there are several extinct species within the extant families. The majority of birds within this order are very large, like ostriches ( Struthio camelus ), which are the largest extant bird species. Ostriches have a wide geographical range, spanning across Australia, South America, and northern Africa. A notable member of the order is Casuarius casuarius , or southern cassowary, which is a highly aggressive, large bird found in New Guinea and Australia. This species is distinguishable by its featherless head, bright blue skin, and two bright red pendulous wattles that hang from the neck.

Geographic Range

Struthioniformes have a wide geographical range, covering most of the Southern hemisphere and a small region within the Northern hemisphere. They are found in the southwestern portion of the Neotropical region ( Rheidae ), the Northwestern portion of the Ethiopean Region ( Struthionidae ), the southeastern region of the Palearctic region ( Struthionidae ), and the Australian region ( Apterygidae , Cassuariidae , Dromaiidae , a small introduced population of Struthionidae , and extinct Dinornthidae ). No members of Struthioniformes are found in the Nearctic nor Oriental regions.

Habitat

Struthioniformes inhabit various habitats. Many reside in dense, tropical rainforests, such as families Casuariidae and Apterygidae . Rheiidea and Struthionidae are found in grasslands and savannahs. The extinct family Dinornithidae was believed to have inhabited the marshlands, grasslands, and forests of New Zealand. Dromiaidae occupies almost every habitat in Australia, avoiding urban areas and desert regions during the dry seasons, though they can be found there when it rains. Most Struthioniformes avoid areas of high urban settlement, but will often be found in areas of agricultural development and roadways. Members of family Casuariidae often have dangerous interactions with humans due to habitat disruption.

Systematic and Taxonomic History

Struthioniformes are in class Aves and subclass Paleognathae . Struthioniformes have a complex taxonomic history. In the past, species were often placed into their own order, which resulted in many different orders for the individual bird species. There is some debate over the classification of Struthioniformes , as some researchers place order Tinamiformes (subclass Paleognathae ), in Struthioniformes . In general, Struthioniformes has a very complicated history and is still heavily debated today.

Physical Description

Struthioniformes are grouped together based on their sternum that lacks a keel, which is a projection of bone found on the sternum of flying birds that provides a space for flight muscles. The raft-like sternum of Struthioniformes gives them the name “ratites," which is a name commonly used for this order. All the birds in the order are flightless and feature long legs that benefit their ground-dwelling behavior. All birds also have brown or black feathers, with a few families having distinct coloration. Ostrich ( Struthio camelus ) males have black or dark brown feathers with striking white plumage at the ends of their wings, tail feathers, and around their necks, which are used for mating displays and hostile encounters. Cassowaries ( Casuarius ) have very distinct coloration, with the three different species having bright coloration on the skin of their neck and a characteristic casque on the top of their head. Northern cassowaries ( Casuarius unappendiculatus ) have bright blue coloration on their necks and heads, with a red waddle on the base of their necks, much like southern cassowaries ( Casuarius casuarius ) and dwarf cassowaries ( Casuarius bennetti ). Unlike its relatives, northern cassowaries ( Casuarius unappendiculatus ) also feature a bright yellow patch on their necks, adding a beautiful contrast between the red of their waddles and the blue bases of their necks.

  • Sexual Dimorphism
  • sexes alike
  • female larger
  • male larger
  • sexes colored or patterned differently
  • male more colorful
  • ornamentation

Reproduction

Struthioniformes typically have multiple mates during a single mating season. Out of all of the groups found within the order, only kiwis ( Apteryx ) have been observed to have monogamous breeding pairs. In most groups, the nests are primarily protected by the males while the females go find more mates. All members of Struthioniformes have been observed to have solitary nests, even those that are social species, such as emus ( Dromaius ).

Struthioniformes ' breeding seasons range throughout the entire year, with the majority of species falling between the months of June through October. Clutch sizes range from small, with kiwis ( Apterygidae ), cassowaries ( Casuariidae ), and ostriches ( Struthionidae ) having clutches of around three to six eggs, to large, with rheas ( Rheidae ) having clutch sizes that have been reported to be in the thirties. Gestation periods for Struthioniformes typically last around a month to two months. Because this order contains flightless birds, young are able to move around on their own within a day or two. Juveniles will typically remain with the parent(s) for several months, and will often remain in the area until adulthood.

Struthioniformes males typically invest more into the offspring than the females. Females will often lay the eggs and incubate them for a week or two, then the males will take over incubation full-time and raise the offspring. During the incubation period, males will consume very little food and water. With ostriches ( Struthionidae ) and two species of kiwi ( Apteryx haastii and Apteryx australis ), males and females will both incubate the eggs. Males and females will also care for the offspring. Juvenile Struthioniformes are able to move around shortly after hatching, due to being a flightless species. Young will stay with their parents for several months, often remaining in the area until adulthood.

  • Parental Investment
  • precocial
  • male parental care
  • pre-fertilization
    • provisioning
    • protecting
      • male
      • female
  • pre-hatching/birth
    • provisioning
      • male
      • female
    • protecting
      • male
      • female
  • pre-independence
    • provisioning
      • male
    • protecting
      • male
      • female
  • extended period of juvenile learning
  • inherits maternal/paternal territory

Lifespan/Longevity

Very little is known about the natural lifespans of Struthioniformes , but most species are estimated to be able live several decades, with most of this information coming from individuals raised in captivity. Struthioniformes ' main predators include big cats, large dog species (i.e. dingos), and crocodilians. Humans also frequently hunt the birds for food and feathers.

Behavior

Struthioniformes have mostly solitary species. Cassowaries ( Casuariidae ), emus ( Dromaiidae ), and kiwis ( Apterygidae ) are solitary species, with kiwis only interacting with conspecifics while breeding in monogamous pairs during the breeding season. Ostriches ( Struthionidae ) and rheas ( Rheidae ) can live in groups, but can also be solitary. Most ostriches live in small family groups or harems. Rheas will form social groups during breeding season, usually returning to a solitary life when the season ends.

Struthioniformes ' behaviors vary between species. Many of the larger species will act very aggressive towards conspecifics, other species, and humans. Almost all but kiwis will show aggression towards humans. The most notorious Struthioniformes are southern cassowaries ( Casuarius casuarius ). Southern cassowaries have very sharp claws on their incredibly thick legs, which they use to violently kick at threats. This bird is often said to be very aggressive, causing many issues with local humans. They are also one of the few birds to have killed a person by directly attacking them. Although these birds have killed several hundred people, most attacks were due to territory issues and food, as people will occasionally feed the wildlife thus causing the cassowaries to associate humans with food.

Communication and Perception

Struthioniformes are fairly understudied in their methods of communication and perception. They have been observed to use a significant amount of acoustic calls to communicate with conspecifics. They also have been seen using body language, such as neck and wing movement, as well as feather-ruffling, to communicate with conspecifics.

Food Habits

Struthioniformes eat a wide range of food, including fruits, insects, worms, vegetation, and seeds. Some species, like southern cassowaries ( C. casuarius ), have been known to scavenge carcasses. Struthioniformes are very important for seed distribution, especially those that reside in dense, forest environments. The passage of fruits and seeds through the digestive tract of these birds has been shown to have a very important role in the germination of forests. Several papers have been published on southern cassowaries and their importance to the rainforests of northern Australia and New Guinea.

Predation

Struthioniformes are well-equipped to deal with predation. These birds are built for speed and defense, with all but kiwis being over five feet tall. Struthioniformes have long legs designed for running. These legs feature very sharp claws on the toes, which are often combined with a very powerful kick to act as an anti-predator defense mechanism. Because Struthioniformes are found all over the world, they have a variety of predators. Most commonly, large cat and dog species such as lions ( Panthera leo ) and dingos ( Canis lupus dingo ) prey on the birds - although in many cases, Struthioniformes are poor targets due to their strong defenses. Their eggs and young are a much easier target. The most dangerous predator for Struthioniformes is probably humans. Humans have been hunting Struthioniformes for thousands of years and are responsible for driving moas ( Dinornithidae ) extinct. Every species that was driven extinct in Struthiuoniformes was the result of anthropogenic impacts.

Ecosystem Roles

Struthioniformes ' ecological roles are largely based on their diet. Struthioniformes consume a majority fruit and vegetation diet, with species residing in tropical environments consuming mostly fruits. Thus, these species play a very important role via seed dispersion. Most species swallow the fruits whole, ingesting the entire fruit. The seeds pass through the gut, undigested, and are dispersed throughout the bird's territory, fertilizing the seeds and allowing them to germinate.

  • Ecosystem Impact
  • disperses seeds

Economic Importance for Humans: Positive

Struthioniformes have had some positive economic impacts on humans. Ostriches, rheas, and emus are farmed for their eggs, plumage, and occasionally meat. Other species are commonly hunted for their plumage. Indigenous peoples used to hunt Struthioniformes for their plumages, as well as for food. In Tanzania, locals harvest ostrich parts for medicinal and commercial use. Struthioniformes are also very popular in zoos for education and tourism. In addition to this, many species are popular in the exotic pet trade, as commercial farms used for tourism usually keep one or more species to attract consumers.

Economic Importance for Humans: Negative

Many species within Struthioniformes are considered agricultural pests, especially emus and kiwis. Because Struthioniformes have frequent interactions with humans due to habitat crossover as well as being raised for farming, there is also a risk of disease transmission from the birds to humans. In addition to this, some larger species will also attack humans if provoked, such as cassowaries and oastriches, both of which have killed humans before.

Conservation Status

Struthioniformes ' populations are on the decline. Their main threats are habitat loss and deforestation, especially for kiwis and cassowaries, both of which have relatively small ranges that are easily disrupted by human activity. Although Struthioniformes are declining and are at risk for becoming endangered, there is conservation action being taken around the world. New Zealand's government is working to protect the kiwis and educate their citizens on the importance of kiwis. Additionally, zoos around the world are working towards conservation efforts for Struthioniformes , as well as working on restoring the native ranges of Struthioniformes and protecting their habitats from destruction.

Encyclopedia of Life

Contributors

Ellie Bollich (author), Colorado State University, Sydney Collins (editor), Colorado State University.

Palearctic

living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.

World Map

native range

the area in which the animal is naturally found, the region in which it is endemic.

Ethiopian

living in sub-Saharan Africa (south of 30 degrees north) and Madagascar.

World Map

native range

the area in which the animal is naturally found, the region in which it is endemic.

Neotropical

living in the southern part of the New World. In other words, Central and South America.

World Map

native range

the area in which the animal is naturally found, the region in which it is endemic.

Australian

Living in Australia, New Zealand, Tasmania, New Guinea and associated islands.

World Map

introduced

referring to animal species that have been transported to and established populations in regions outside of their natural range, usually through human action.

native range

the area in which the animal is naturally found, the region in which it is endemic.

island endemic

animals that live only on an island or set of islands.

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

terrestrial

Living on the ground.

desert or dunes

in deserts low (less than 30 cm per year) and unpredictable rainfall results in landscapes dominated by plants and animals adapted to aridity. Vegetation is typically sparse, though spectacular blooms may occur following rain. Deserts can be cold or warm and daily temperates typically fluctuate. In dune areas vegetation is also sparse and conditions are dry. This is because sand does not hold water well so little is available to plants. In dunes near seas and oceans this is compounded by the influence of salt in the air and soil. Salt limits the ability of plants to take up water through their roots.

tropical savanna and grassland

A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.

savanna

A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.

temperate grassland

A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.

chaparral

Found in coastal areas between 30 and 40 degrees latitude, in areas with a Mediterranean climate. Vegetation is dominated by stands of dense, spiny shrubs with tough (hard or waxy) evergreen leaves. May be maintained by periodic fire. In South America it includes the scrub ecotone between forest and paramo.

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

rainforest

rainforests, both temperate and tropical, are dominated by trees often forming a closed canopy with little light reaching the ground. Epiphytes and climbing plants are also abundant. Precipitation is typically not limiting, but may be somewhat seasonal.

scrub forest

scrub forests develop in areas that experience dry seasons.

mountains

This terrestrial biome includes summits of high mountains, either without vegetation or covered by low, tundra-like vegetation.

marsh

marshes are wetland areas often dominated by grasses and reeds.

swamp

a wetland area that may be permanently or intermittently covered in water, often dominated by woody vegetation.

agricultural

living in landscapes dominated by human agriculture.

riparian

Referring to something living or located adjacent to a waterbody (usually, but not always, a river or stream).

endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

sexual ornamentation

one of the sexes (usually males) has special physical structures used in courting the other sex or fighting the same sex. For example: antlers, elongated tails, special spurs.

monogamous

Having one mate at a time.

polyandrous

Referring to a mating system in which a female mates with several males during one breeding season (compare polygynous).

polygynous

having more than one female as a mate at one time

polygynandrous

the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.

cooperative breeder

helpers provide assistance in raising young that are not their own

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

seasonal breeding

breeding is confined to a particular season

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

fertilization

union of egg and spermatozoan

internal fertilization

fertilization takes place within the female's body

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

young precocial

young are relatively well-developed when born

male parental care

parental care is carried out by males

diurnal
  1. active during the day, 2. lasting for one day.
nocturnal

active during the night

motile

having the capacity to move from one place to another.

nomadic

generally wanders from place to place, usually within a well-defined range.

migratory

makes seasonal movements between breeding and wintering grounds

sedentary

remains in the same area

solitary

lives alone

territorial

defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement

social

associates with others of its species; forms social groups.

colonial

used loosely to describe any group of organisms living together or in close proximity to each other - for example nesting shorebirds that live in large colonies. More specifically refers to a group of organisms in which members act as specialized subunits (a continuous, modular society) - as in clonal organisms.

dominance hierarchies

ranking system or pecking order among members of a long-term social group, where dominance status affects access to resources or mates

visual

uses sight to communicate

acoustic

uses sound to communicate

pet trade

the business of buying and selling animals for people to keep in their homes as pets.

food

A substance that provides both nutrients and energy to a living thing.

ecotourism

humans benefit economically by promoting tourism that focuses on the appreciation of natural areas or animals. Ecotourism implies that there are existing programs that profit from the appreciation of natural areas or animals.

drug

a substance used for the diagnosis, cure, mitigation, treatment, or prevention of disease

causes or carries domestic animal disease

either directly causes, or indirectly transmits, a disease to a domestic animal

carnivore

an animal that mainly eats meat

insectivore

An animal that eats mainly insects or spiders.

scavenger

an animal that mainly eats dead animals

herbivore

An animal that eats mainly plants or parts of plants.

folivore

an animal that mainly eats leaves.

frugivore

an animal that mainly eats fruit

granivore

an animal that mainly eats seeds

omnivore

an animal that mainly eats all kinds of things, including plants and animals

visual

uses sight to communicate

tactile

uses touch to communicate

acoustic

uses sound to communicate

chemical

uses smells or other chemicals to communicate

References

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Bradford, M., D. Westcott. 2010. Consequences of southern cassowary (Casuarius casuarius, L.) gut passage and deposition pattern on the germination of rainforest seeds. Austral Ecology , Volume 35, Issue 3: 325-333.

Cholewiak, D. 2003. "Rheidae" (On-line). Animal Diversity Web. Accessed March 23, 2022 at https://animaldiversity.org/accounts/Rheidae/ .

Cooper, R., K. Mahrose, J. Horbanczuk, R. Villeguz-Vizcaino, S. Kenou Sebei, A. Faki Mohammed. 2009. The wild ostrich (Struthio camelus): a review. Tropical Animal Health and Production , Volume 41: 1669.

Cramp, S., K. Simmons, I. Ferguson-Lees, R. Gillmor, P. Hollom, R. Hudson, E. Nicholson, M. Ogilvie, P. Olney, K. Voous, J. Wattel. 1977. Handbook of the Birds of Europe the Middle East and North Africa . Oxford: Oxford University Press.

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Kofron, C. 1999. Attacks to humans and domestic animals by the southern cassowary (Casuarius casuarius johnsonii) in Queensland, Australia. Journal Of Zoology , Volume 249, Issue 4: 375-381. Accessed February 05, 2022 at https://www-webofscience-com.ezproxy2.library.colostate.edu/wos/woscc/full-record/WOS:000084429000001 .

Magige, F., E. Roskaft. 2017. "Medicinal and Commercial Uses of Ostrich Products in Tanzania" (On-line). Accessed April 13, 2022 at https://pubmed.ncbi.nlm.nih.gov/28835266/ .

Marchant, S., P. Higgins. 1990. Handbook of Australian, New Zealand, and Antarctic Birds, Volume 1 . Australia: Oxford University Press.

Naish, D. 2018. "How Dangerous are Cassowaries, Really?" (On-line). Scientific American. Accessed April 01, 2022 at https://blogs.scientificamerican.com/tetrapod-zoology/how-dangerous-are-cassowaries-really/ .

Olson, V., S. Turvey. 2013. The evolution of sexual dimorphism in New Zealand giant moa (Dinornis) and other ratites. Proceedings of the Royal Society B , Volume 280, Issue 1760: 20130401.

Ryeland, J., T. Derham, R. Spencer. 2021. Past and future potential range changes in one of the last large vertebrates of the Australian continent, the emu Dromaius novaehollandiae. Scientific Reports , Volume 11: 851.

Taborsky, M., B. Taborsky. 1995. Habitat Use and Selectivity by the Brown Kiwi (Apteryx australis mantelli) in a Patchy Environment. The Auk , Volume 112, Issue 3: 680-689.

Worthy, T. 2017. "Moa - Distribution" (On-line). The Encyclopedia of New Zealand. Accessed February 13, 2022 at https://teara.govt.nz/en/moa/page-2 .

2022. "Dinornithidae" (On-line). Animal Diversity Web. Accessed February 12, 2022 at https://animaldiversity.org/accounts/Dinornithidae/classification/#Dinornithidae .

2016. "Greater Rhea" (On-line). IUCN Redlist. Accessed February 13, 2022 at https://www.iucnredlist.org/species/22678073/92754472 .

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2022. "Keel" (On-line). Oxford Reference. Accessed March 23, 2022 at https://www.oxfordreference.com/view/10.1093/oi/authority.20110810105209696 .

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To cite this page: Bollich, E. 2022. "Struthioniformes" (On-line), Animal Diversity Web. Accessed {%B %d, %Y} at https://animaldiversity.org/accounts/Struthioniformes/

Last updated: 2022-27-22 / Generated: 2025-11-24 03:00

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