Editing Nuthatch (section)

===Nesting, breeding and survival===
[[File:NuthatchNest.svg|thumb|right| Cross-section of a western rock nuthatch nest cavity with a mud wall and tunnel across its entrance]]
[[File:White-breasted nuthatch creating cavity.webm|thumb|thumbtime=105|A [[white-breasted nuthatch]] creating a cavity through the fibrous tissue in the stub of a pruned dead [[Canary Island Date Palm]] frond.]]
All nuthatches nest in cavities; except for the two species of rock nuthatches, all use tree holes, making a simple cup lined with soft materials on which to rest eggs. In some species the lining consists of small woody objects such as bark flakes and seed husks, while in others it includes the moss, grass, hair and feathers typical of passerine birds.<ref name="HQeurasian"/><ref name="HQpigmy"/>

Members of the red-breasted nuthatch superspecies excavate their own tree holes, although most other nuthatches use natural holes or old [[woodpecker]] nests. Several species reduce the size of the entrance hole and seal up cracks with mud. The red-breasted nuthatch makes the nest secure by daubing sticky conifer [[resin]] globules around the entrance, the male applying the resin outside and the female inside. The resin may deter predators or competitors (the resident birds avoid the resin by diving straight through the entrance hole).<ref name="Cornellrbn">{{cite web| title= Red-breasted Nuthatch | work= Bird Guide | url= http://www.birds.cornell.edu/AllAboutBirds/BirdGuide/Red-breasted_Nuthatch_dtl.html| publisher= Cornell Laboratory of Ornithology | access-date=2008-06-20}}</ref> The white-breasted nuthatch smears [[blister beetle]]s around the entrance to its nest, and it has been suggested that the unpleasant smell from the crushed insects deters [[squirrel]]s, its chief competitor for natural tree cavities.<ref name="Kilham">{{cite journal| last= Kilham | first= Lawrence |date=January 1971 | title= Use of in bill-sweeping by White-breasted Nuthatch | journal= The Auk | volume=88 | issue= 1 | pages= 175–176 | url =http://sora.unm.edu/sites/default/files/journals/auk/v088n01/p0175-p0176.pdf | doi= 10.2307/4083981| jstor= 4083981 }}</ref>

The western rock nuthatch builds an elaborate flask-shaped nest from mud, dung and hair or feathers, and decorates the nest's exterior and nearby crevices with feathers and insect wings. The nests are located in rock crevices, in caves, under cliff overhangs or on buildings.<ref name="HQwrock"/> The eastern rock nuthatch builds a similar but less complex structure across the entrance to a cavity. Its nest can be quite small but may weigh up to 32&nbsp;[[kilogram|kg]] (70&nbsp;[[pound (mass)|lb]]). This species will also nest in river banks or tree holes and will enlarge its nest hole if it the cavity is too small.<ref name="HQerock"/>

[[File:Dendrocopos major 4-3c.jpg|upright|thumb|left|The [[great spotted woodpecker]] is an important predator of Eurasian nuthatch nests.<ref name="Varo">{{cite journal| last=González-Varo | first= Juan P |author2=López-Bao, José V.|author3=Guitián, José | year=2008 | title= Presence and abundance of the Eurasian nuthatch ''Sitta europaea'' in relation to the size, isolation and the intensity of management of chestnut woodlands in the NW Iberian Peninsula | journal= Landscape Ecology | volume= 23| issue= 1 | pages=79–89 | doi =10.1007/s10980-007-9166-7| bibcode= 2008LaEco..23...79G | s2cid= 19446422 }}</ref>]]
Nuthatches are [[monogamy in animals|monogamous]]. The female produces eggs that are white with red or yellow markings; the clutch size varies, tending to be larger for northern species. The eggs are incubated for 12 to 18 days by the female alone, or by both parents, depending on the species. The [[altricial]] (naked and helpless) chicks take between 21 and 27 days to fledge.<ref name="HQerock"/><ref name="BWP1406">Snow & Perrins (1998) pp. 1406–1407 "Rock Nuthatch"</ref><ref name="BWPintro">Snow & Perrins (1998) p. 1398 "Nuthatch: Family Sittidae"</ref><ref name="Matthysen & Löhrl">{{cite book | last = Matthysen | first = Erik | author2 = Löhrl, Hans | chapter = Nuthatches | editor = Perrins, Christopher | editor-link = Christopher Perrins | title = Firefly Encyclopedia of Birds | publisher = Firefly Books | year = 2003 | pages = [https://archive.org/details/fireflyencyclope0000unse/page/536 536–537] | isbn = 978-1-55297-777-4 | chapter-url-access = registration | chapter-url = https://archive.org/details/fireflyencyclope0000unse | url = https://archive.org/details/fireflyencyclope0000unse/page/536 }}</ref> Both parents feed the young, and in the case of two American species, brown-headed and pygmy, [[helpers at the nest|helper]] males from the previous brood may assist the parents in feeding.<ref name="ADWpygmy"/><ref name="Cornellbhn">{{cite web| title= Brown-headed Nuthatch | work= Bird Guide | url= http://www.birds.cornell.edu/AllAboutBirds/BirdGuide/Brown-headed_Nuthatch_dtl.html | publisher= Cornell Laboratory of Ornithology | access-date=2008-06-21}}</ref>

For the few species on which data are available, the average nuthatch lifespan in the wild is between 2 and 3.5&nbsp;years, although ages of up to 10 years have been recorded.<ref name="ADWpygmy">{{cite web| author = Kieliszewski, Jordan | title= ''Sitta pygmaea'' | work= Animal Diversity Web| url= http://animaldiversity.ummz.umich.edu/site/accounts/information/Sitta_pygmaea.html | publisher= University of Michigan Museum of Zoology | access-date=2008-06-21}}</ref><ref name="ADWwbn">{{cite web|author1=Roof, Jennifer |author2=Dewey, Tanya | title= ''Sitta carolinensis'' | work= Animal Diversity Web| url= http://animaldiversity.ummz.umich.edu/site/accounts/information/Sitta_carolinensis.html | publisher= University of Michigan Museum of Zoology | access-date=2008-06-21}}</ref> The Eurasian nuthatch has an adult annual [[survival rate]] of 53%<ref name="BTO">{{cite web| title= Nuthatch ''Sitta europaea'' [Linnaeus, 1758&#93; | work= BTO Birdfacts | url= http://blx1.bto.org/birdfacts/results/bob14790.htm | publisher= [[British Trust for Ornithology]]| access-date=2008-12-01}}</ref> and the male Corsican nuthatch 61.6%.<ref name="Thibault">{{cite journal| last= Thibault | first= Jean-Claude |author2=Jenouvrier, Stephanie  | year=2006 | title= Annual survival rates of adult male Corsican nuthatches ''Sitta whiteheadi'' | journal= [[Ringing & Migration]] | volume= 23 | pages= 85–88 | url = http://blx1.bto.org/pdf/ringmigration/23_2/thibault.pdf | doi= 10.1080/03078698.2006.9674349| issue= 2| s2cid= 85182636 | doi-access= free }}</ref> Nuthatches and other small woodland birds share the same predators: [[accipiter]]s, [[owl]]s, squirrels and woodpeckers. An American study showed that nuthatch responses to predators may be linked to reproductive strategies. It measured the willingness of males of two species to feed incubating females on the nest when presented with models of a [[sharp-shinned hawk]], which hunts adult nuthatches, or a [[Northern house wren|house wren]], which destroys eggs. The white-breasted nuthatch is shorter-lived than the red-breasted nuthatch, but has more young, and was found to respond more strongly to the egg predator, whereas the red-breasted showed greater concern with the hawk. This supports the theory that longer-lived species benefit from adult survival and future breeding opportunities while birds with shorter life spans place more value on the survival of their larger broods.<ref name="Ghalambor">{{cite journal| last= Ghalambor | first= Cameron K. |author2=Martin, Thomas E.  |date=August 2000 | title= Parental investment strategies in two species of nuthatch vary with stage-specific predation risk and reproductive effort | journal=Animal Behaviour | volume=60| pmid= 10973729 | issue=2 | pages=263–267 | url = http://www.umt.edu/mcwru/personnel/martin/PDF%20Martin/Reprint577.pdf | doi =10.1006/anbe.2000.1472| s2cid= 13165711 }}</ref>

Cold can be a problem for small birds that do not migrate. [[Communal roosting]] in tight huddles can help conserve heat and several nuthatch species employ it&mdash;up to 170 pygmy nuthatches have been seen in a single roost. The pygmy nuthatch is able to lower its body temperature when roosting, conserving energy through [[hypothermia]] and a lowered [[basal metabolic rate|metabolic rate]].<ref name="ADWpygmy"/>