Editing Emu (section)

=== Breeding ===
[[File:Emu Egg.JPG|thumb|alt=Emu egg|Dark green emu egg]]

Emus form breeding pairs during the summer months of December and January and may remain together for about five months. During this time, they stay in an area a few kilometres in diameter and it is believed they find and defend territory within this area. Both males and females put on weight during the breeding season, with the female becoming slightly heavier at between {{convert|45|and|58|kg|lb|abbr=on}}. Mating usually takes place between April and June; the exact timing is determined by the climate as the birds nest during the coolest part of the year.<ref name=e23 /> During the breeding season, males experience hormonal changes, including an increase in [[luteinizing hormone|luteinising hormone]] and [[testosterone]] levels, and their [[testicle]]s double in size.<ref>{{cite journal|doi=10.1016/S0378-4320(98)00110-9 |author1=Malecki, I.A. |author2=Martin, G.B. |author3=O'Malley, P.J. |author4=Meyer, G.T. |author5=Talbot, R.T. |author6=Sharp, P.J. |year=1998 |title=Endocrine and testicular changes in a short-day seasonally breeding bird, the emu (''Dromaius novaehollandiae''), in southwestern Australia |journal=Animal Reproduction Science |volume=53 |issue=1–4 |pages=143–155 |pmid=9835373 }}</ref>

Males construct a rough nest in a semi-sheltered hollow on the ground, using bark, grass, sticks and leaves to line it.<ref name=Davies /> The nest is almost always a flat surface rather than a segment of a sphere, although in cold conditions the nest is taller, up to {{convert|7|cm|abbr=on}} tall, and more spherical to provide some extra heat retention. When other material is lacking, the bird sometimes uses a [[Triodia (grass)|spinifex tussock]] a metre or so across, despite the prickly nature of the foliage.<ref name=e23 /> The nest can be placed on open ground or near a shrub or rock. The nest is usually placed in an area where the emu has a clear view of its surroundings and can detect approaching predators.<ref name=e24>Eastman, p. 24.</ref> The nest can contain eggs from multiple emus the number is usually between 15 and 25 eggs.<ref>{{Cite web |title=Emu |url=https://nationalzoo.si.edu/animals/emu |access-date=2024-03-21 |website=Smithsonian's National Zoo and Conservation Biology Institute |language=en}}</ref>

Female emus court the males; the female's plumage darkens slightly and the small patches of bare, featherless skin just below the eyes and near the beak turn turquoise-blue. The colour of the male's plumage remains unchanged, although the bare patches of skin also turn light blue.  When courting, females stride around, pulling their neck back while puffing out their feathers and emitting low, monosyllabic calls that have been compared to drum beats. This calling can occur when males are out of sight or more than {{convert|50|m|ft|-1}} away.  Once the male's attention has been gained, the female circles her prospective mate at a distance of {{convert|10|to|40|m|ft|-1}}. As she does this, she looks at him by turning her neck, while at the same time keeping her rump facing towards him. If the male shows interest in the parading female, he will move closer; the female continues the courtship by shuffling further away but continuing to circle him.<ref name=e23 /><ref name=Coddington/>

If a male is interested, he will stretch his neck and erect his feathers, then bend over and peck at the ground. He will circle around and sidle up to the female, swaying his body and neck from side to side, and rubbing his breast against his partner's rump. Often the female will reject his advances with aggression, but if amenable, she signals acceptance by squatting down and raising her rump.<ref name=Coddington/><ref name=Patodkar>{{cite journal |author1=Patodkar, V.R. |author2=Rahane, S.D. |author3=Shejal, M.A. |author4=Belhekar, D.R. |year=2011 |title=Behavior of emu bird (''Dromaius novaehollandiae'') |journal=Veterinary World |volume=2 |issue=11 |pages=439–440 |url=http://www.veterinaryworld.org/Vol.2/November/9.html }}</ref>

[[File:Emu Gelege.jpg|right|thumb|alt=Nest and eggs|Nest and eggs]]

Females are more aggressive than males during the courtship period, often fighting for access to mates, with fights among females accounting for more than half the aggressive interactions during this period.  If females court a male that already has a partner, the incumbent female will try to repel the competitor, usually by chasing and kicking.  These interactions can be prolonged, lasting up to five hours, especially when the male being fought over is single and neither female has the advantage of incumbency. In these cases, the females typically intensify their calls and displays.<ref name=Coddington/>

The sperm from a mating is stored by the female and can suffice to fertilise about six eggs.<ref name=Patodkar/> The pair mate every day or two, and every second or third day the female lays one of a clutch of five to fifteen very large, thick-shelled, green eggs. The shell is around {{convert|1|mm|in|2|abbr=on}} thick, but rather thinner in northern regions according to indigenous Australians.<ref name=Davies /><ref name=e24 /> The shell is substantially composed of [[calcite]], and its [[δ13C|δ{{sup|13}}C]] is a function of the emu's diet.<ref name="Lynch-et-al-2007" /> The eggs are on average {{convert|13|x|9|cm|in|abbr=on}} and weigh between {{convert|450|and|650|g|lb|1|abbr=on}}.<ref name=Campbell>{{cite book|author1=Campbell, Bruce |author2=Lack, Elizabeth |title=A Dictionary of Birds |url=https://books.google.com/books?id=kZqJAAAAQBAJ&pg=PA179 |year=2013 |publisher=Bloomsbury Publishing |isbn=978-1-4081-3839-7 |page=179}}</ref> The maternal investment in the egg is considerable, and the proportion of yolk to [[Egg white|albumen]], at about 50%, is greater than would be predicted for a precocial egg of this size. This probably relates to the long [[Egg incubation#Avian incubation|incubation]] period which means the developing chick must consume greater resources before hatching.<ref>{{cite journal |author=Dzialowski, Edward M. |author2=Sotherland, Paul R. |year=2004 |title=Maternal effects of egg size on emu ''Dromaius novaehollandiae'' egg composition and hatchling phenotype |journal=Journal of Experimental Biology |volume=207 |issue=4 |pages=597–606 |doi=10.1242/jeb.00792 |pmid=14718503 |doi-access=free |bibcode=2004JExpB.207..597D }}</ref> The first verified occurrence of genetically identical avian twins was demonstrated in the emu.<ref>{{cite journal |doi=10.1111/j.1469-7998.1999.tb01010.x |author1=Bassett, S.M. |author2=Potter, M.A. |author3=Fordham, R.A. |author4=Johnston, E.V. |year=1999 |title=Genetically identical avian twins |journal=Journal of Zoology |volume=247 |pages=475–478 |issue=4 }}</ref> The egg surface is granulated and pale green. During the incubation period, the egg turns dark green, although if the egg never hatches, it will turn white from the [[bleach]]ing effect of the sun.<ref name=e25>Eastman, p. 25.</ref>

The male becomes broody after his mate starts laying, and may begin to incubate the eggs before the clutch is complete. From this time on, he does not eat, drink, or defecate, and stands only to turn the eggs, which he does about ten times a day.<ref name=e25 /> He develops a [[brood patch]], a bare area of wrinkled skin which is in intimate contact with the eggs.<ref>{{cite book|title=The Emu|url=https://books.google.com/books?id=m8ogAQAAMAAJ |year=1956 |author=Royal Australasian Ornithologists' Union |publisher=The Union |page=408}}</ref> Over the course of the eight-week incubation period, he will lose a third of his weight and will survive on stored body fat and on any morning dew that he can reach from the nest. As with many other Australian birds, such as the [[superb fairywren]], infidelity is the norm for emus, despite the initial pair bond: once the male starts brooding, the female usually wanders off, and may mate with other males and lay in multiple nests; thus, as many as half the chicks in a brood may not be fathered by the incubating male, or even by either parent, as emus also exhibit [[Brood parasite|brood parasitism]].<ref>{{cite journal|author1=Taylor, Emma L. |author2=Blache, Dominique |author3=Groth, David |author4=Wetherall, John D. |author5=Martin, Graeme B. |year=2000 |title=Genetic evidence for mixed parentage in nests of the emu (''Dromaius novaehollandiae'') |journal=Behavioral Ecology and Sociobiology |volume=47 |issue=5 |pages=359–364 |jstor=4601755 |doi=10.1007/s002650050677|bibcode=2000BEcoS..47..359T |s2cid=20313464 }}</ref>

[[File:Baby Emu.jpg|thumb|alt=Chicks are camouflaged|Emu chicks have longitudinal stripes that provide camouflage]]

Some females stay and defend the nest until the chicks start hatching, but most leave the nesting area completely to nest again; in a good season, a female emu may nest three times.<ref name="Congress">{{cite book |author=Davies, S.J.J.F. |year=1976 |chapter=The natural history of the emu in comparison with that of other ratites |title=Proceedings of the 16th international ornithological congress |editor1=Firth, H.J. |editor2=Calaby, J.H. |publisher=[[Australian Academy of Science]] |pages=109–120 |isbn=978-0-85847-038-5}}</ref> If the parents stay together during the incubation period, they will take turns standing guard over the eggs while the other drinks and feeds within earshot.<ref name=e26 /> If it perceives a threat during this period, it will lie down on top of the nest and try to blend in with the similar-looking surrounds, and suddenly stand up to confront and scare the other party if it comes close.<ref name=e26>Eastman, p. 26.</ref>

Incubation takes 56&nbsp;days, and the male stops incubating the eggs shortly before they hatch.<ref name="Congress" /> The temperature of the nest rises slightly during the eight-week period. Although the eggs are laid sequentially, they tend to hatch within two days of one another, as the eggs that were laid later experienced higher temperatures and developed more rapidly.<ref name=Maloney2008/> During the process, the [[precocial]] emu chicks need to develop a capacity for thermoregulation. During incubation, the embryos are kept at a constant temperature but the chicks will need to be able to cope with varying external temperatures by the time they hatch.<ref name=Maloney2008/>

Newly hatched chicks are active and can leave the nest within a few days of hatching. They stand about {{convert|12|cm|in|0|abbr=on}} tall at first, weigh {{convert|0.5|kg|oz|1|abbr=on}},<ref name="S. Davies" /> and have distinctive brown and cream stripes for camouflage, which fade after three months or so. The male guards the growing chicks for up to seven months, teaching them how to find food.<ref name="S. Davies" /><ref name="Reader's Digest">{{cite book|title=Reader's Digest Complete Book of Australian Birds|publisher=Reader's Digest Services |isbn= 978-0-909486-63-1|title-link=Reader's Digest Complete Book of Australian Birds |year=1978 }}</ref> Chicks grow very quickly and are fully grown in five to six months;<ref name="S. Davies" /> they may remain with their family group for another six months or so before they split up to breed in their second season. During their early life, the young emus are defended by their father, who adopts a belligerent stance towards other emus, including the mother. He does this by ruffling his feathers, emitting sharp grunts, and kicking his legs to drive off other animals. He can also bend his knees to crouch over smaller chicks to protect them. At night, he envelops his young with his feathers.<ref name=e27>Eastman, p. 27.</ref> As the young emus cannot travel far, the parents must choose an area with plentiful food in which to breed.<ref name=e31 /> In the wild, emus can live for upwards of 10 years but in captivity, they can live up to 20 years.<ref name=HBWA/><ref>Blakers, M., S. Davies, P. Reilly. 1984. The Atlas of Australian Birds. Melbourne, Australia: Melbourne University Press.</ref>