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Immature birds have dull grey-brown plumage on their heads, wings, and backs, with numerous pale spots. Their underparts are paler and streaked with brown. The young birds have orange eyes and duller yellowish-green legs. They are very noisy birds in their nesting colonies, with calls that are commonly transcribed as {{Not a typo|''quok''}} or {{Not a typo|''woc''}}.
'''Measurements''':<ref>{{Cite web|title=Black-crowned Night- Heron Identification, All About Birds, Cornell Lab of Ornithology|url=https://www.allaboutbirds.org/guide/Black-crowned_Night-Heron/id|access-date=2020-09-26|website=www.allaboutbirds.org|language=en}}</ref>
* '''Length''': {{cvt|22.8|–|26|in|cm}}
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This heron is [[bird migration|migratory]] in the northernmost part of its range, but otherwise resident (even in the cold [[Patagonia]]). The North American population winters in Mexico, the southern United States, Central America, and the West Indies, and the Old World birds winter in tropical Africa and southern Asia.
A colony of the herons has regularly summered at the [[National Zoological Park (United States)|National Zoo]] in [[Washington, D.C.]] for more than a century.<ref name="Smithsonian’s mystery of the black-crowned night- herons solved by satellites">{{cite web|last1=Akpan|first1=Nsikan|date=12 May 2015|title=Smithsonian's mystery of the black-crowned night- herons solved by satellites|url=https://www.pbs.org/newshour/rundown/sciencescope-smithsonians-mystery-black-crowned-night-herons-solved-satellites/|website=[[PBS NewsHour]]|publisher=PBS|access-date=2 May 2016}}</ref> The birds also prominently live year-round in the shores around the [[San Francisco Bay]], with the largest rookery in [[Oakland, California|Oakland]].<ref name=":0">{{Cite web|date=2019-05-24|title=Oakland Has Its First Official Bird Thanks to These Dedicated Kids|url=https://www.audubon.org/news/oakland-has-its-first-official-bird-thanks-these-dedicated-kids|access-date=2021-06-19|website=Audubon|language=en}}</ref> Their ever presence at Oakland's [[Lake Merritt]] and throughout the city's downtown area, as well as their resilience to the urban environment and displacement efforts, have led to them being named Oakland's official city bird.<ref name=":0" />
=== Status in Great Britain ===
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== Behaviour ==
[[File:Black-crowned night heron (61438).jpg|thumb|upright=0.8| Juvenile in an "upright" threat display]]
These birds stand still at the water's edge and wait to ambush prey, mainly at night or early morning. They primarily eat small [[fish]], [[leech]]es, [[earthworm]]s, [[mussel]]s, [[squid]],<ref name="animaldiversity.org">{{cite web | url=https://animaldiversity.org/accounts/Nycticorax_nycticorax/ | title=Nycticorax nycticorax (Blackblack-crowned night- heron) | website=[[Animal Diversity Web]] }}</ref> [[crustacean]]s (such as [[crayfish]]),<ref name="animaldiversity.org"/> [[frog]]s, other [[amphibian]]s,<ref name="animaldiversity.org"/> [[aquatic insect]]s, terrestrial insects, [[lizard]]s, [[snake]]s,<ref name="animaldiversity.org"/> small [[mammal]]s (such as [[rodent]]s),<ref name="animaldiversity.org"/> small [[bird]]s, [[egg]]s, [[carrion]], [[plant]] material, and [[garbage]] and refuse at [[landfill]]s.<ref name="animaldiversity.org"/> They are among the seven heron species observed to engage in bait fishing; luring or distracting fish by tossing edible or inedible buoyant objects into water within their striking range – a rare example of tool use among birds.<ref>{{Cite journal|last=Riehl|first=Christina|date=2001|title=Black-Crowned Night- Heron Fishes with Bait|jstor=1522044|journal=Waterbirds: The International Journal of Waterbird Biology|volume=24|issue=2|pages=285–286|doi=10.2307/1522044}}</ref><ref>{{Cite journal|last1=Ruxton|first1=Graeme D.|last2=Hansell|first2=Michael H.|date=2011-01-01|title=Fishing with a Bait or Lure: A Brief Review of the Cognitive Issues|journal=Ethology|language=en|volume=117|issue=1|pages=1–9|doi=10.1111/j.1439-0310.2010.01848.x|bibcode=2011Ethol.117....1R |issn=1439-0310}}</ref> During the day they rest in trees or bushes. ''N. n. hoactli'' is more gregarious outside the breeding season than the [[Subspecies|nominate race]].
== Parasites ==
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{{commons}}
* {{cite web | last1=Blasco-Zumeta | first1=Javier | last2=Heinze | first2=Gerd-Michael | work=Identification Atlas of Aragon's Birds | title=Black-crowned Night Heron | url=http://blascozumeta.com/wp-content/uploads/aragon-birds/non-passeriformes/037.nightheron-nnycticorax.pdf | access-date=1 June 2018 | archive-date=25 October 2018 | archive-url=https://web.archive.org/web/20181025071051/http://blascozumeta.com/wp-content/uploads/aragon-birds/non-passeriformes/037.nightheron-nnycticorax.pdf | url-status=dead }}
* [httphttps://www.birdsallaboutbirds.cornell.eduorg/AllAboutBirds/BirdGuideguide/Black-crowned_Night-Heron.htmlcrowned_Night_Heron Black-crowned Night- Heron Species Account] – Cornell Lab of Ornithology
* [http://www.mbr-pwrc.usgs.gov/id/framlst/i2020id.html Black-crowned night-heron - ''Nycticorax nycticorax''] - USGS Patuxent Bird Identification InfoCenter
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