Editing Bird nest (section)

=== Mound ===
[[File:Malleefowl mound.jpg|alt=A large pile of bare earth stands amidst pale tree trunks, bleached grass and fallen sticks.|The huge mound nest of the [[malleefowl]] acts like a compost heap, warming and incubating the eggs as it rots around them.|thumb|right]]

Burying eggs as a form of incubation reaches its zenith with the [[Australasia]]n [[megapode]]s. Several megapode species construct enormous ''mound'' nests made of soil, branches, sticks, twigs and leaves, and lay their eggs within the rotting mass. The heat generated by these mounds, which are in effect giant [[compost heap]]s, warms and incubates the eggs.<ref name="Campbell386"/> The nest heat results from the respiration of thermophilic fungi and other [[microorganism]]s.<ref name="HBW2-287"/> The size of some of these mounds can be truly staggering; several of the largest—which contain more than {{convert|100|m3|yd3}} of material, and probably weigh more than 50 tons (45,000&nbsp;kg)<ref name="HBW2-287">{{Harvnb|Elliott|1994|p=287}}</ref>—were initially thought to be [[Indigenous Australians|Aboriginal]] middens.{{sfn|Hansell|2000|p=9}}

In most mound-building species, males do most or all of the nest construction and maintenance. Using his strong legs and feet, the male scrapes together material from the area around his chosen nest site, gradually building a [[cone (geometry)|conical]] or bell-shaped pile. This process can take five to seven hours a day for more than a month. While mounds are typically reused for multiple breeding seasons, new material must be added each year to generate the appropriate amount of heat. A female will begin to lay eggs in the nest only when the mound's temperature has reached an optimal level.<ref name="HBW2-288">{{Harvnb|Elliott|1994|p=288}}</ref>

[[File:Slimbridge.chilean.flamingo.arp.jpg|thumb|left|upright|alt=Two long-legged, long-necked pink birds stand atop cylindrical piles of mud, with water in the background.|The mound nests of flamingos, like these [[Chilean flamingo]]s, help to protect their eggs from fluctuating water levels.]]

Both the temperature and the moisture content of the mound are critical to the survival and development of the eggs, so both are carefully regulated for the entire length of the breeding season (which may last for as long as eight months), principally by the male.<ref name="HBW2-287"/> [[Ornithologist]]s believe that megapodes may use sensitive areas in their mouths to assess mound temperatures; each day during the breeding season, the male digs a pit into his mound and sticks his head in.<ref>{{Harvnb|Elliott|1994|p=280}}</ref> If the mound's core temperature is a bit low, he adds fresh moist material to the mound, and stirs it in; if it is too high, he opens the top of the mound to allow some of the excess heat to escape. This regular monitoring also keeps the mound's material from becoming compacted, which would inhibit oxygen diffusion to the eggs and make it more difficult for the chicks to emerge after hatching.<ref name="HBW2-288"/> The [[malleefowl]], which lives in more open forest than do other megapodes, uses the sun to help warm its nest as well—opening the mound at midday during the cool spring and autumn months to expose the plentiful sand incorporated into the nest to the sun's warming rays, then using that warm sand to insulate the eggs during the cold nights. During hot summer months, the malleefowl opens its nest mound only in the cool early morning hours, allowing excess heat to escape before recovering the mound completely.<ref>{{Harvnb|Elliott|1994|p=289}}</ref> One recent study showed that the sex ratio of [[Australian brushturkey]] hatchlings correlated strongly with mound temperatures; females hatched from eggs incubated at higher mean temperatures.<ref>{{Citation |last=Göth |first=Anne |title=Incubation temperatures and sex ratios in Australian brush-turkey (''Alectura lathami'') mounds |journal=Austral Ecology |year=2007 |volume=32 |issue=4 |pages=278–285 |doi=10.1111/j.1442-9993.2007.01709.x|bibcode=2007AusEc..32..378G }}</ref>

[[Flamingo]]s make a different type of mound nest. Using their [[beak]]s to pull material towards them,<ref name = "delHoyo516">{{Harvnb|del Hoyo|1992|p=516}}</ref> they fashion a cone-shaped pile of mud between {{convert|15|–|46|cm|in|round=0.5|abbr=on}} tall, with a small depression in the top to house their single egg.<ref>{{Harvnb|Seng|2001|p=188}}</ref> The height of the nest varies with the substrate upon which it is built; those on [[clay]] sites are taller on average than those on dry or sandy sites.<ref name = "delHoyo516"/> The height of the nest and the circular, often water-filled trench which surrounds it (the result of the removal of material for the nest) help to protect the egg from fluctuating water levels and excessive heat at ground level. In East Africa, for example, temperatures at the top of the nest mound average some {{convert|20|°C-change|abbr=on}} cooler than those of the surrounding ground.<ref name = "delHoyo516"/>

The base of the [[horned coot]]'s enormous nest is a mound built of stones, gathered one at a time by the pair, using their beaks. These stones, which may weigh as much as 450 g (about a pound) each, are dropped into the shallow water of a lake, making a [[Cone (geometry)|cone]]-shaped pile which can measure as much as {{convert|4|m2|ft2|abbr=on}} at the bottom and {{convert|1|m2|ft2|abbr=on}} at the top, and {{convert|0.6|m|ft|abbr=on}} in height. The total combined weight of the mound's stones may approach 1.5 tons (1,400&nbsp;kg). Once the mound has been completed, a sizable platform of aquatic vegetation is constructed on top. The entire structure is typically reused for many years.<ref>{{Citation|title=Rails |first1=Barry |last1=Taylor |first2=Ber |last2=van Perlo |year=1998 |publisher=Pica Press |location=Sussex |isbn=978-1-873403-59-4 |page=557}}</ref>