Editing Bird nest (section)

=== Cavity ===
[[File:Forpus xanthopterygius -tree hole -Brazil-8.jpg|thumb|"Secondary cavity nesters", like this [[cobalt-rumped parrotlet]], use natural cavities or holes excavated by other species.]]

The ''cavity'' nest is a chamber, typically in living or dead wood, but sometimes in the trunks of [[tree fern]]s<ref name="HBW6-94">{{Harvnb|Collar|2001|p=94}}</ref> or large [[cactus|cacti]], including [[Carnegiea|saguaro]].<ref name="HBW6-94"/><ref name = "WP"/> In tropical areas, cavities are sometimes excavated in arboreal insect nests.<ref>{{Citation |last=Brightsmith |first=Donald J. |title=Use of Arboreal Termitaria by Nesting Peruvian Amazon |journal=Condor |year=2000 |volume=102 |issue=3 |pages=529–538 |url=http://sora.unm.edu/sites/default/files/journals/condor/v102n03/p0529-p0538.pdf |doi=10.1650/0010-5422(2000)102[0529:UOATBN]2.0.CO;2 |s2cid=52541280 |url-status=live |archive-url=https://web.archive.org/web/20160128025203/http://sora.unm.edu/sites/default/files/journals/condor/v102n03/p0529-p0538.pdf |archive-date=28 January 2016 }}</ref><ref name = "HBW6-96">{{Harvnb|Collar|2001|p=96}}</ref> A relatively small number of species, including [[woodpecker]]s, [[trogon]]s, some [[nuthatch]]es and many [[Ramphastides|barbets]], can excavate their own cavities. Far more species—including parrots, [[Paridae|tit]]s, [[bluebird]]s, most [[hornbill]]s, some kingfishers, some [[true owl|owl]]s, some ducks and some flycatchers—use natural cavities, or those abandoned by species able to excavate them; they also sometimes usurp cavity nests from their excavating owners. Those species that excavate their own cavities are known as "primary cavity nesters", while those that use natural cavities or those excavated by other species are called "secondary cavity nesters". Both primary and secondary cavity nesters can be enticed to use [[nest box]]es (also known as bird houses); these mimic natural cavities, and can be critical to the survival of species in areas where natural cavities are lacking.<ref>{{Citation |journal=BirdScope |date=Winter 2005 |title=Nest Boxes: More than Just Birdhouses |last=Phillips |first=Tina |volume=19 |issue=1 |url=http://www.birds.cornell.edu/Publications/Birdscope/Winter2005/nest_boxes.html |url-status=live |archive-url=https://web.archive.org/web/20070719060059/http://www.birds.cornell.edu/Publications/Birdscope/winter2005/nest_boxes.html |archive-date=19 July 2007 }}</ref>

Woodpeckers use their chisel-like bills to excavate their cavity nests, a process which takes, on average, about two weeks.<ref name = "WP">{{Harvnb|Reed|2001|pp=380–1}}</ref> Cavities are normally excavated on the downward-facing side of a branch, presumably to make it more difficult for predators to access the nest, and to reduce the chance that rain floods the nest.<ref name = "Conner">{{Harvnb|Conner|1975|p=373}}</ref> There is also some evidence that fungal rot may make the wood on the underside of leaning trunks and branches easier to excavate.<ref name = "Conner"/> Most woodpeckers use a cavity for only a single year. The endangered [[red-cockaded woodpecker]] is an exception; it takes far longer—up to two years—to excavate its nest cavity, and may reuse it for more than two decades.<ref name = "WP"/> The typical woodpecker nest has a short horizontal tunnel which leads to a vertical chamber within the trunk. The size and shape of the chamber depends on species, and the entrance hole is typically only as large as is needed to allow access for the adult birds. While wood chips are removed during the excavation process, most species line the floor of the cavity with a fresh bed of them before laying their eggs.

[[File:BlackWoods.jpg|thumb|left|Only a relatively small number of species, including the woodpeckers, are capable of excavating their own cavity nests.]]

Trogons excavate their nests by chewing cavities into very soft dead wood; some species make completely enclosed chambers (accessed by upward-slanting entrance tunnels), while others—like the extravagantly plumed [[resplendent quetzal]]—construct more open niches.<ref name="HBW6-96"/> In most trogon species, both sexes help with nest construction. The process may take several months, and a single pair may start several excavations before finding a tree or stump with wood of the right consistency.

Species which use natural cavities or old woodpecker nests sometimes line the cavity with soft material such as grass, moss, lichen, feathers or fur. Though a number of studies have attempted to determine whether secondary cavity nesters preferentially choose cavities with entrance holes facing certain directions, the results remain inconclusive.<ref name="Rendell">{{citation |last1=Rendell |first1=Wallace B. |last2=Robertson |first2=Raleigh J. |title=Cavity Entry Orientation and Nest-site Use by Secondary Hole-nesting Birds |journal=Journal of Field Ornithology |year=1994 |volume=65 |pages=27–35 |issue=1 |url=http://sora.unm.edu/sites/default/files/journals/jfo/v065n01/p0027-p0035.pdf |url-status=live |archive-url=https://web.archive.org/web/20160304210619/http://sora.unm.edu/sites/default/files/journals/jfo/v065n01/p0027-p0035.pdf |archive-date=4 March 2016 }}</ref> While some species appear to preferentially choose holes with certain orientations, studies (to date) have not shown consistent differences in fledging rates between nests oriented in different directions.<ref name = "Rendell"/>

Cavity-dwelling species have to contend with the danger of predators accessing their nest, catching them and their young inside and unable to get out.<ref>{{Citation |title=New Generation Guide to the Birds of Britain and Europe |first1=Christopher M |last1=Perrins |first3=Norman |last3=Arlott |first2=David |last2=Attenborough |year=1987 |publisher=University of Texas Press |page=230 |location=Austin, TX |isbn=978-0-292-75532-1}}</ref> They have a variety of methods for decreasing the likelihood of this happening. Red-cockaded woodpeckers peel bark around the entrance, and drill wells above and below the hole; since they nest in live trees, the resulting flow of resin forms a barrier that prevents snakes from reaching the nests.<ref>{{harvnb|Rudolph|Kyle|Conner|1990}}</ref> [[Red-breasted nuthatch]]es smear sap around the entrance holes to their nests, while [[white-breasted nuthatch]]es rub foul-smelling insects around theirs.<ref>{{Harvnb|Reed|2001|p=437}}</ref> [[Eurasian nuthatch]]es wall up part of their entrance holes with mud, decreasing the size and sometimes extending the tunnel part of the chamber. Most female hornbills seal themselves into their cavity nests, using a combination of mud (in some species brought by their mates), food remains and their own droppings to reduce the entrance hole to a narrow slit.<ref>{{Harvnb|Kemp|2001|p=469}}</ref>

A few birds are known to use the nests of insects within which they create a cavity in which they lay their eggs. These include the [[rufous woodpecker]] which nests in the arboreal nests of ''[[Crematogaster]]'' ants and the [[collared kingfisher]] which uses termite nests.<ref>{{Cite journal|last=Moreau|first=R. E.|date=1936|title=XXVI.-Bird-Insect Nesting Associations|journal=Ibis|language=en|volume=78|issue=3|pages=460–471|doi=10.1111/j.1474-919X.1936.tb03399.x}}</ref>

In December 2024, scientists reported that birds that build their nests in cavities are more than six times more likely to incorporate snakeskin into their nests than those which build cup-shaped nests. The same study found that the snake skin helped deter predators from eggs during their incubation period.<ref>{{Cite news |last=Golembiewski |first=Kate |date=2025-01-25 |title=Snakeskin Isn’t Just a Fashion Statement for Birds |url=https://www.nytimes.com/2025/01/25/science/snakeskin-birds-nests.html |access-date=2025-01-30 |work=The New York Times |language=en-US |issn=0362-4331}}</ref>