Editing Kākāpō (section)

===Breeding===
[[File:Kakapo egg hatching.jpg|thumb|left|Hatching kākāpō egg]]

Kākāpō are the only flightless bird that has a [[lek (mating arena)|lek]] breeding system.<ref name="CFGNZW">{{cite book |title=Collins Field Guide to New Zealand Wildlife |first1=Terrence |last1=Lindsey |first2=Rod |last2=Morris |publisher=HarperCollins New Zealand |year=2000 |isbn=978-1-86950-300-0}}</ref> Males loosely gather in an arena and compete with each other to attract females. Females listen to the males as they display, or "lek".<ref name="Merton77">{{cite book |author-link=Don Merton |author=Merton, D. V. |year=1976 |chapter=Conservation of the kakapo: A progress report. |title=Proc. Science in Nat. Parks. |publisher=National Parks Authority |location=Wellington, N.Z. |series=National Parks Series |volume=6 |pages=139–148}}</ref> They choose a mate based on the quality of his display; they are not pursued by the males in any overt way. No pair bond is formed; males and females meet only to mate.<ref>{{Cite news |last=Deborah |first=Sloan |date=22 Oct 2008 |title=Scientists study smelly birds |pages=14 |work=[[Taranaki Daily News]] }}</ref>

During the courting season, males leave their home ranges for hilltops and ridges where they establish their own mating courts. These leks can be up to {{convert|5|km|mi|0}} from a kākāpō's usual territory and are an average of {{Convert|50|m|ft|-1}} apart within the lek arena. Males remain in the region of their court throughout the courting season. At the start of the breeding season, males will fight to try to secure the best courts. They confront each other with raised feathers, spread wings, open beaks, raised claws and loud screeching and growling. Fighting may leave birds with injuries or even kill them. Mating occurs only approximately every five years, with the ripening of the [[rimu]] fruit. In mating years, males may make "booming" calls for 6–8 hours every night for more than four months.<ref>{{cite journal |doi=10.1017/S0959270900001933 |last1=Clout |first1=M. N. |last2=Merton |first2=D. V. |author-link2=Don Merton |date=1998 |title=Saving the kakapo: The conservation of the world's most peculiar parrot |journal=Bird Conservation International |volume=8 |issue=3 |pages=281–295|doi-access=free }}</ref>

[[File:051226-kakapo-billbooming.ogg|thumb|The sound of a kākāpō booming]]
Each court consists of one or more saucer-shaped depressions or "bowls" dug in the ground by the male, up to {{Convert|10|cm|in|0}} deep and long enough to fit the half-metre length of the bird. The kākāpō is one of only a handful of birds in the world which actually constructs its leks.<ref name="CFGNZW"/> Bowls are often created next to rock faces, banks, or tree trunks to help reflect sound:<ref name="Merton1984">{{Cite journal |last1=Merton |first1=D. V. |author-link1=Don Merton |last2=Morris |first2=R. B. |last3=Atkinson |first3=I. A. |date=1984 |title=Lek behaviour in a parrot: the kakapo ''Strigops habroptilus'' of New Zealand. |journal=[[Ibis (journal)|Ibis]] |volume=126 |issue=3 |pages=277–283 |doi=10.1111/j.1474-919X.1984.tb00250.x}}</ref> the bowls themselves function as amplifiers to enhance the projection of the males' booming mating calls.<ref name="CFGNZW"/> Each male's bowls are connected by a network of trails or tracks which may extend {{Convert|50|m|ft|-1}} along a ridge or {{Convert|20|m|ft|-1}} in diameter around a hilltop. Males meticulously clear their bowls and tracks of debris.<ref name="Merton1984"/>

To attract females, males make loud, low-frequency (below 100{{nbsp}}[[Hertz|Hz]]) booming calls from their bowls by inflating a [[thorax|thoracic]] sac.{{sfn|Higgins|1999|pp=639, 641}}<ref name="Cockrem2002">{{cite journal |last=Cockrem |first=J. F. |title=Reproductive biology and conservation of the endangered kakapo (''Strigops habroptilus'') in New Zealand |journal=Avian and Poultry Biology Reviews |date=2002 |volume=13 |issue=3 |pages=139–144 |doi=10.3184/147020602783698548}}</ref> They start with low grunts, which increase in volume as the sac inflates. After a sequence of about 20 loud booms, the male kākāpō emits a high-frequency, metallic "ching" sound.<ref>{{cite web |title=Meet the kakapo: Breeding |url=http://kakaporecovery.org.nz/breeding/ |website=Kakapo Recovery |access-date=3 September 2013}}</ref> He stands for a short while before again lowering his head, inflating his chest and starting another sequence of booms. The booms can be heard at least {{Convert|1|km|mi}} away on a still night; wind can carry the sound at least {{Convert|5|km|mi}}.<ref name="Merton1984"/> {{citation needed span|Males boom for an average of eight hours a night; each male may produce thousands of booms in this time. This may continue every night for three or four months during which time the male may lose half his body weight. Each male moves around the bowls in his court so that the booms are sent out in different directions. These booms are also notorious for attracting predators, because of the long range at which they can be heard.|date=December 2022}}

Females are attracted by the booms of the competing males; they too may need to walk several kilometres from their territories to the arena. Once a female enters the court of one of the males, the male performs a display in which he rocks from side to side and makes clicking noises with his beak.<ref name="Powlesland2006"/> He turns his back to the female, spreads his wings in display and walks backwards towards her. He will then attempt copulation for 40 minutes or more.<ref name="Ballance20180">{{cite book |last=Ballance |first=Alison |author-link=Alison Ballance |title=Kākāpō: rescued from the brink of extinction |publisher=Potton and Burton |year=2018 |isbn=9781877517273 |edition=2nd revised |location=Nelson, New Zealand}}</ref> Once the birds have mated, the female returns to her home territory to lay eggs and raise the chicks. The male continues booming in the hope of attracting another female.{{sfn|Higgins|1999|p=638}}

[[File:Kakapo chicks.jpg|thumb|Hatchlings]] 
The female kākāpō lays 1–4 eggs per breeding cycle, with several days between eggs.<ref name="Cockrem2002"/><ref name="Ballance20180" /> The nest is placed on the ground under the cover of plants or in cavities such as hollow tree trunks. The female incubates the eggs beginning after the first egg is laid, but is forced to leave the nest every night in search of food. Predators are known to eat the eggs, and the embryos inside can also die of cold in the mother's absence. Kākāpō eggs usually hatch within 30 days,<ref name="Easton2006">{{cite journal |title=Breeding biology of kakapo (''Strigops habroptilus'') on offshore island sanctuaries, 1990–2002 |last1=Eason |first1=D.K. |last2=Elliott |first2=G.P. |last3=Merton |first3=D.V. |author-link3=Don Merton |last4=Jansen |first4=P.W. |last5=Harper |first5=G.A. |last6=Moorhouse |first6=R.J. |journal=Notornis |volume=54 |issue=1 |date=2006 |pages=27–36 |url=https://www.birdsnz.org.nz/wp-content/uploads/2021/12/Notornis_53_1_27.pdf }}</ref> bearing fluffy grey chicks that are quite helpless. The female feeds the chicks for three months, and the chicks remain with the female for some months after [[fledge|fledging]].<ref name="Cockrem2002"/> The young chicks are just as vulnerable to predators as the eggs, and young have been killed by many of the same predators that attack adults. Chicks leave the nest at approximately 10 to 12 weeks of age. As they gain greater independence, their mothers may feed the chicks sporadically for up to 3 months.<ref name="Powlesland2006"/>{{sfn|Higgins|1999|p=643}}

The kākāpō is long-lived, with an average life expectancy of 60 (plus or minus 20) years, and tends to reach adolescence before it starts breeding.<ref name="Ballance20180" /> Males start booming at about 5 years of age.{{sfn|Higgins|1999|p=640}} It was thought that females reached [[sexual maturity]] at 9 years of age, but four five-year-old females have now been recorded reproducing.<ref name="Easton2006"/><ref name="Ballance20180" /> The kākāpō does not breed every year and has one of the lowest rates of reproduction among birds. Breeding occurs only in years when trees mast (fruit heavily), providing a plentiful food supply. Rimu mast occurs only every three to five years, so in rimu-dominant forests, such as those on Whenua Hou, kākāpō breeding occurs as infrequently.<ref>{{cite journal |title=Nutrient composition of the diet of parent-raised kakapo nestlings |first1=Yvette |last1=Cottam |first2=Don V. |last2=Merton  |author-link2=Don Merton |first3=Wouter |last3=Hendriks |pages=90–99|journal=Notornis |volume=53 |issue=1 |year=2006 |url=https://www.birdsnz.org.nz/wp-content/uploads/2021/12/Notornis_53_1_90.pdf }}</ref>

Another aspect of the kākāpō's breeding system is that a female can alter the sex ratio of her offspring depending on her condition. A female in good condition produces more male offspring (males have 30%–40% more body weight than females).<ref name="Powlesland2006"/> Females produce offspring biased towards the dispersive sex when competition for resources (such as food) is high and towards the non-dispersive sex when food is plentiful. A female kākāpō will likely be able to produce eggs even when there are few resources, while a male kākāpō will be more capable of perpetuating the species when there are plenty, by mating with several females.<ref name="berkeley_kakapo_reproduction">{{cite web |url=http://evolution.berkeley.edu/evolibrary/news/060401_kakapo |title=Conserving the kakapo |access-date=22 March 2008 |date=April 2006 |work=Understanding Evolution |publisher=University of California, Berkeley}}</ref> This supports the [[Trivers–Willard hypothesis]]. The relationship between clutch sex ratio and maternal diet has conservation implications, because a captive population maintained on a high quality diet will produce fewer females and therefore fewer individuals valuable to the recovery of the species.<ref name="sutherland-sciencesexkakapo">{{cite journal |last=Sutherland |first=William J. |title=Conservation biology: Science, sex and the kakapo |journal=Nature |volume=419 |year=2002 |pages=265–266 |doi=10.1038/419265a |pmid=12239554 |issue=6904|bibcode=2002Natur.419..265S |s2cid=52871178 |doi-access=free }}</ref>