Editing Kiwi (bird) (section)

==Behaviour and ecology==
Before the arrival of humans in the 13th century or earlier, New Zealand's only endemic mammals were [[List of mammals of New Zealand#Order: Chiroptera (bats)|three species of bat]], and the [[ecological niche]]s that in other parts of the world were filled by creatures as diverse as horses, wolves and mice were taken up by birds (and, to a lesser extent, reptiles, insects and gastropods).<ref>{{cite magazine|last1=Kolbert|first1=Elizabeth|title=The Big Kill|url=http://www.newyorker.com/magazine/2014/12/22/big-kill|access-date=16 December 2014|magazine=[[The New Yorker]]|date=22 December 2014|archive-date=16 December 2014|archive-url=https://web.archive.org/web/20141216050041/http://www.newyorker.com/magazine/2014/12/22/big-kill|url-status=live}}</ref>

The kiwi's mostly nocturnal habits may be a result of habitat intrusion by predators, including humans. In areas of New Zealand where introduced predators have been removed, such as sanctuaries, kiwi are often seen in daylight. They prefer subtropical and temperate [[podocarp]] and beech forests, but they are being forced to adapt to different habitat, such as sub-alpine scrub, tussock grassland, and the mountains.<ref name="Davies" /> Kiwi have a highly developed sense of smell, unusual in a bird, and are the only birds with nostrils at the end of their long beaks. Kiwi eat small invertebrates, seeds, grubs, and many varieties of worms. They also may eat fruit, small crayfish, eels and amphibians. Because their nostrils are located at the end of their long beaks, kiwi can locate insects and worms underground using their keen sense of smell, without actually seeing or feeling them.<ref name="Davies" /> This sense of smell is due to a highly developed olfactory chamber and surrounding regions. It is a common belief that the kiwi relies solely on its sense of smell to catch prey, but this has not been scientifically observed. Lab experiments have suggested that ''A. australis'' can rely on olfaction alone but is not consistent under natural conditions. Instead, the kiwi may rely on auditory and/or vibrotactile cues.<ref>{{Cite journal |last1=Cunningham |first1=Susan |last2=Castro |first2=Isabel |author-link2=Isabel Castro (biologist) |last3=Alley |first3=Maurice |date=1 October 2007 |title=A new prey-detection mechanism for kiwi (Apteryx spp.) suggests convergent evolution between paleognathous and neognathous birds |journal=Journal of Anatomy |language=en |volume=211 |issue=4 |pages=493–502 |doi=10.1111/j.1469-7580.2007.00786.x |issn=1469-7580 |pmc=2375824 |pmid=17711422}}</ref>

[[File:KiwiEggRatio.svg|upright|thumb|Relative size of the [[Bird egg|egg]]]]

=== Mating and breeding ===
Once bonded, a male and female kiwi tend to live their entire lives as a monogamous couple. During the mating season, June to March, the pair call to each other at night, and meet in the nesting burrow every three days. These relationships may last for up to 20&nbsp;years.<ref>{{Citation | url = http://SavetheKiwi.org.nz/ | title = Save the Kiwi | access-date = 3 July 2021 | archive-date = 10 June 2015 | archive-url = https://web.archive.org/web/20150610090610/http://savethekiwi.org.nz/ | url-status = live }}, formerly Kiwi Recovery.</ref> They are unusual among other birds in that, along with some raptors, they have a functioning pair of [[ovaries]]. (In most birds and in [[platypus]]es, the right ovary never matures, so that only the left is functional.<ref name="Davies" /><ref>Fitzpatrick, F.L., (1934). Unilateral and bilateral ovaries in raptorial birds. The Wilson Bulletin, 46(1): 19–22</ref><ref>Kinsky, F.C., (1971). The consistent presence of paired ovaries in the Kiwi (Apteryx) with some discussion of this condition in other birds. Journal of Ornithology 112(3): 334–357.</ref>).

Usually, only one egg is laid per season. The kiwi lays one of the largest eggs in proportion to its size of any bird in the world,<ref>{{Citation | publisher = Auckland Zoo | title = Official Guide Book | chapter = Wilderness New Zealand}}</ref>{{efn|Some petrels may exceed this.<ref>{{cite web |last1=Kerry-Jayne |first1=Kerry-Jayne |title=Petrels, Breeding |url=https://teara.govt.nz/en/petrels/page-2 |website=Te Ara |publisher=Te Ara – the Encyclopedia of New Zealand |access-date=13 April 2019 |archive-date=12 April 2019 |archive-url=https://web.archive.org/web/20190412083507/https://teara.govt.nz/en/petrels/page-2 |url-status=live }}</ref><ref>{{cite journal |last1=Sanz-Aguilar |first1=Ana |title=Is Laying a Large Egg Expensive? Female-Biased Cost of First Reproduction in a Petrel |journal=The Auk |volume=129 |issue=3 |pages=510–516 |publisher=BioOne Complete |doi=10.1525/auk.2012.12011 |year=2012 |url=https://digital.csic.es/bitstream/10261/99097/1/Sanz-The-Auk-2012-v129-n3-p510.pdf |hdl=10261/99097 |s2cid=27277394 |hdl-access=free |access-date=24 September 2019 |archive-date=8 March 2021 |archive-url=https://web.archive.org/web/20210308074910/https://digital.csic.es/bitstream/10261/99097/1/Sanz-The-Auk-2012-v129-n3-p510.pdf |url-status=live }}</ref>}} so even though the kiwi is about the size of a domestic chicken, it is able to lay eggs that are about six times the size of a chicken's egg.<ref>{{Citation | url = http://Savethekiwi.org/ | title = Save the kiwi | url-status = dead | archive-url = https://web.archive.org/web/20110924103747/http://www.savethekiwi.org/ | archive-date = 24 September 2011}}</ref> Kiwi eggs can weigh up to one-quarter the weight of the female, helped by their inability to fly that could limit the extent by its body weight; brown kiwi females carry and lay a single egg that may weigh as much as {{convert|450|g|oz|abbr=on}}.<ref name="Davies"/> The eggs are smooth in texture, and are ivory or greenish white.<ref name="kiwiweb">{{cite web | url = http://www.chemistry.co.nz/kiwibird.htm | title = The Kiwi Bird, New Zealand's Indigenous Flightless Bird | access-date = 16 January 2009 | archive-url = https://web.archive.org/web/20100210185436/http://www.chemistry.co.nz/kiwibird.htm | archive-date = 10 February 2010 | url-status = dead}}</ref> The male incubates the egg, except for the great spotted kiwi, ''A. haastii'', in which both parents are involved. The incubation period is 63–92&nbsp;days.<ref name="Davies" /> Producing the huge egg places significant physiological stress on the female; for the thirty days it takes to grow the fully developed egg, the female must eat three times her normal amount of food. Two to three days before the egg is laid there is little space left inside the female for her stomach and she is forced to fast.<ref>{{Citation | last = Piper | first = Ross | year = 2007 | title = Extraordinary Animals: An Encyclopedia of Curious and Unusual Animals | publisher = Greenwood Press}}</ref>

It was believed that the large eggs were a trait of much larger [[moa]]-like ancestors, and that kiwi retained large eggs as an evolutionarily neutral trait as they became smaller. However, research in the early 2010s suggested that kiwi were descended from smaller flighted birds that flew to New Zealand and Madagascar, where they gave rise to kiwi and elephant birds. The large egg is instead thought to be an adaptation for [[Precociality|precocity]], enabling kiwi chicks to hatch mobile and with yolk to sustain them for two and half weeks. The large eggs would be safe in New Zealand's historical absence of egg-eating ground predators, while the mobile chicks would be able to evade chick-eating flying predators.<ref name="Audubon_Dean">{{Cite web |last=Dean |first=Sam |date=2015-02-25 |title=Why Is the Kiwi's Egg So Big? |url=https://www.audubon.org/news/why-kiwis-egg-so-big |url-status=live |archive-url=https://web.archive.org/web/20210524073536/https://www.audubon.org/news/why-kiwis-egg-so-big |archive-date=2021-05-24 |access-date=2021-10-20 |website=Audubon |language=en}}</ref>