Animal Diversity Web

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. (Beehler, et al., 2016; "Di­nor­nithi­dae", 2022; Fuller, 1987; Marchant and Hig­gins, 1990)

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. (Beehler, et al., 2016; Bel­lis, et al., 2004; Marchant and Hig­gins, 1990; Rye­land, et al., 2021; Taborsky and Taborsky, 1995; Wor­thy, 2017)

• Biogeographic Regions
• palearctic
  • native
• ethiopian
  • native
• neotropical
  • native
• australian
  • introduced
  • native

• Other Geographic Terms
• island endemic

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. (Beehler, et al., 2016; Bel­lis, et al., 2004; Kofron, 1999; Marchant and Hig­gins, 1990; Taborsky and Taborsky, 1995; Wor­thy, 2017)

• Habitat Regions
• temperate
• tropical
• terrestrial

• Terrestrial Biomes
• desert or dune
• savanna or grassland
• chaparral
• forest
• rainforest
• scrub forest
• mountains

• Wetlands
• marsh
• swamp

• Other Habitat Features
• agricultural
• riparian

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. (Beehler, et al., 2016; Brad­ford and West­cott, 2010; Cramp, et al., 1977; Fuller, 1987; "IUCN Red List of Threat­ened Species", 2021; Marchant and Hig­gins, 1990)

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. (Beehler, et al., 2016; Cramp, et al., 1977; Marchant and Hig­gins, 1990; Olson and Tur­vey, 2013)

• Other Physical Features
• endothermic
• homoiothermic
• bilateral symmetry

• 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). (Beehler, et al., 2016; Cramp, et al., 1977; Fuller, 1987; Marchant and Hig­gins, 1990)

• Mating System
• monogamous
• polyandrous
• polygynous
• polygynandrous (promiscuous)
• cooperative breeder

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. (Beehler, et al., 2016; Cholewiak, 2003; Cramp, et al., 1977; Fuller, 1987; Marchant and Hig­gins, 1990)

• Key Reproductive Features
• iteroparous
• seasonal breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual
• fertilization
  • internal
• oviparous

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. (Beehler, et al., 2016; Cholewiak, 2003; Cramp, et al., 1977; Marchant and Hig­gins, 1990)

• 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. (Beehler, et al., 2016; Brad­ford and West­cott, 2010; Cramp, et al., 1977; Fuller, 1987; Marchant and Hig­gins, 1990)

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. (Beehler, et al., 2016; Cramp, et al., 1977; Fuller, 1987; Marchant and Hig­gins, 1990)

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. (Beehler, et al., 2016; Cramp, et al., 1977; Fuller, 1987; Hodges, 2018; Kofron, 1999; Marchant and Hig­gins, 1990; Naish, 2018)

• Key Behaviors
• cursorial
• terricolous
• diurnal
• nocturnal
• motile
• nomadic
• migratory
• sedentary
• solitary
• territorial
• social
• colonial
• dominance hierarchies

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. (Beehler, et al., 2016; Cramp, et al., 1977; Fuller, 1987; Hodges, 2018; Marchant and Hig­gins, 1990)

• Communication Channels
• visual
• acoustic

• Perception Channels
• visual
• tactile
• acoustic
• chemical

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. (Beehler, et al., 2016; Brad­ford and West­cott, 2010; Cramp, et al., 1977; Fuller, 1987; Hodges, 2018; Marchant and Hig­gins, 1990)

• Primary Diet
• carnivore
  • insectivore
  • eats non-insect arthropods
  • scavenger
• herbivore
  • folivore
  • frugivore
  • granivore
• omnivore

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. (Beehler, et al., 2016; Cramp, et al., 1977; Fuller, 1987; Marchant and Hig­gins, 1990)

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. (Beehler, et al., 2016; Brad­ford and West­cott, 2010; Cramp, et al., 1977; Fuller, 1987; Marchant and Hig­gins, 1990)

• 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. (Beehler, et al., 2016; Brad­ford and West­cott, 2010; Cramp, et al., 1977; Fuller, 1987; Magige and Roskaft, 2017; Marchant and Hig­gins, 1990)

• Positive Impacts
• pet trade
• food
• body parts are source of valuable material
• ecotourism
• source of medicine or drug
• research and education

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. (Beehler, et al., 2016; Brad­ford and West­cott, 2010; Cramp, et al., 1977; Fuller, 1987; "Greater Rhea", 2016; "Lesser Rhea", 2018; Marchant and Hig­gins, 1990)

• Negative Impacts
• injures humans
  • carries human disease
• crop pest
• causes or carries domestic animal disease

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. (Beehler, et al., 2016; Brad­ford and West­cott, 2010; Cramp, et al., 1977; "Di­nor­nithi­dae", 2022; Fuller, 1987; "Greater Rhea", 2016; "IUCN Red List of Threat­ened Species", 2021; "Lesser Rhea", 2018; Marchant and Hig­gins, 1990; "North African Os­trich Re­cov­ery Pro­ject", 2020; "Our Work With Kiwi: New Zealand Na­tive Land Birds", 2018; Wor­thy, 2017)

• IUCN Red List [Link]

  Not Evaluated

Con­trib­u­tors

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

Ref­er­ences

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

2021. "IUCN Red List of Threat­ened Species" (On-line). Ac­cessed April 25, 2022 at https://​www.​iucnredlist.​org/​search?​taxonomies=22672859&​searchType=species.

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2018. "Lesser Rhea" (On-line). IUCN Redlist. Ac­cessed Feb­ru­ary 13, 2022 at https://​www.​iucnredlist.​org/​species/​22728199/​132179491.

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