Animal Diversity Web

Ge­o­graphic Range

The black-crowned night heron is found across North Amer­ica from Wash­ing­ton through Que­bec, south through coastal Mex­ico, as well as lo­cally in Cen­tral Amer­ica and the Caribbean. Some win­ter as far north as Ore­gon and the New Eng­land states. The Old World race 'nyc­ti­co­rax' oc­curs from Eu­rope to Japan, Africa and India. (Davis, 1993)

• Biogeographic Regions
• nearctic
  • native
• palearctic
  • native
• oriental
  • native
• ethiopian
  • native
• neotropical
  • native

Habi­tat

Most colonies of black-crowned night herons are as­so­ci­ated with large wet­lands. They in­habit a va­ri­ety of wet­land habi­tats such as swamps, streams, rivers, marshes, mud flats and the edges of lakes that have be­come over­grown with rushes and cat­tails. (Davis, 1993; http://​www.​biology.​ualberta.​ca/​uamz.​hp/​heron.​html)

Phys­i­cal De­scrip­tion

The night heron has a stocky body, with a com­par­a­tively short neck and legs. The length av­er­ages 58-72 cm, with the fe­males av­er­ag­ing slightly smaller than the males. The adult has dis­tinc­tive col­or­ing, with black cap, upper back and scapu­lars; gray wings, rump and tail; and white to pale gray un­der­parts. The bill is stout and black, and the eyes are red. For most of the year, the legs of the adult are yel­low-green, but by the height of the breed­ing sea­son, they have turned pink. The eyes of the ju­ve­nile black-crowned night heron are yel­low­ish or amber, and the dull gray legs lack the col­or­ful pig­men­ta­tion of those of the adult. The ju­ve­nile has a brown head, neck, chest and belly streaked with buff and white. The wings and back are darker brown, though the tips of the feath­ers have large white spots. These spots are par­tic­u­larly large on the greater sec­ondary coverts. The young do not ac­quire full adult plumage until the third year. (Davis, 1993; http://​www.​mbr.​nbs.​gov/​id/​htmid/​h2020id.​html)

• Other Physical Features
• endothermic
• bilateral symmetry

• Average mass

  800 g

  28.19 oz

  AnAge

Re­pro­duc­tion

Black-crowned night herons are pre­sumed to be monog­a­mous. Pair for­ma­tions are sig­naled by males be­com­ing ag­gres­sive and per­form­ing Snap Dis­plays, in which they walk around in a crouched po­si­tion, head low­ered, snap­ping their mandibles to­gether or grasp­ing a twig. The Snap Dis­play is fol­lowed by the Ad­ver­tise­ment Dis­play--some­times called the Stretch, Snap-hiss, or Song and Dance dis­play--to at­tract fe­males. In this dis­play a male stretches his neck out and bobs his head, and when his head is level with his feet, he gives a snap-hiss vo­cal­iza­tion. Twig-shak­ing and preen­ing may be occur be­tween songs. It has been sug­gested that these dis­plays pro­vide so­cial stim­u­lus to other birds, prompt­ing them to dis­play. This sti­m­ul­tion in colo­nial species may be cru­cial for suc­cess­ful re­pro­duc­tion. Fe­males that come near the dis­play­ing male are re­jected at first, but even­tu­ally a fe­male is al­lowed to enter his ter­ri­tory. The newly-formed pair then al­lo­preens and en­gages in mu­tual billing. At the time of pair for­ma­tion, the legs of both sexes turn pink. Cop­u­la­tion usu­ally takes place on or near the nest, and be­gins the first or sec­ond day after the pair is formed.

There is one brood per sea­son. Black-crowned night herons nest colo­nially, and often there can be more than a dozen nests in one tree. The nest is built near the trunk of a tree or in the fork of branches, ei­ther in the open or deep in fo­liage. The male ini­ti­ates nest build­ing by be­gin­ning to build a new nest or re­fur­bish­ing an old one. The nest is usu­ally a plat­form lined with roots and grass. Dur­ing and after pair for­ma­tion, the male col­lects sticks and pre­sents them to the fe­male, who works them into the nest. The male's twig cer­e­mony grad­u­ally changes to nest build­ing.

The eggs are laid at 2 day in­ter­vals, be­gin­ning 4-5 days after pair for­ma­tion. In­cu­ba­tion, which lasts 24-26 days, is car­ried out by both adults. The clutch size is 3-5 eggs. The eggs are green­est on the first day and fade to pale blue or green after that. On hot days, the par­ents wet their feath­ers, per­haps to keep the eggs cool. Both par­ents brood the young. After 2 weeks, the young leave the nest, al­though they don't go far. By 3 weeks, they can be found clus­tered at the tops of trees if they are dis­turbed. By Week 6-7 they fly well and de­part for the feed­ing grounds. Adult black-crowned night herons do not rec­og­nize their own young and will ac­cept and brood young from other nests. The young have a ten­dancy to re­gur­gi­tate their food onto in­trud­ers when dis­turbed. (Davis, 1993)

• Key Reproductive Features
• iteroparous
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual
• oviparous

• Average eggs per season

  4

  AnAge

• Average time to hatching

  25 days

  AnAge

• Average age at sexual or reproductive maturity (female)
  Sex: female

  730 days

  AnAge

• Average age at sexual or reproductive maturity (male)
  Sex: male

  730 days

  AnAge

Lifes­pan/Longevity

• Average lifespan
  Status: wild

  253 months

  Bird Banding Laboratory

Be­hav­ior

Black-crowned night herons are so­cial at all times of the year, as­so­ci­at­ing with other species of herons fre­quently. In the win­ter, it roosts com­mu­nally. It is a mi­grat­ing species. The nor­mal call is a 'Qua,' 'Quak,' or 'Quark.' These calls are most often given in flight or from a perch. The fact that this night heron feeds through­out the night means that it avoids com­pe­ti­tion with day herons which use the same habi­tat. Feed­ing sites are used re­peat­edly. When feed­ing, it alights on water feet first, or plunges from the air. When walk­ing, it usu­ally keeps its head and neck low­ered, and it rarely runs. It may re­tract its feet when fly­ing on cold days in order to con­serve heat. The young leave their perches and hud­dle in the nest when cold. Black-crowned night herons de­fend both feed­ing and nest­ing ter­ri­tory. The young can be ag­gres­sive, re­gur­gi­tat­ing or defe­cat­ing on human in­trud­ers. (Davis, 1993)

• Key Behaviors
• flies
• motile

Com­mu­ni­ca­tion and Per­cep­tion

• Perception Channels
• visual
• tactile
• acoustic
• chemical

Food Habits

The black-crowned night heron is an op­por­tunis­tic feeder. Its diet con­sists mainly of fish, though it is fre­quently rounded out by other items such as leeches, earth­worms, aquatic and ter­res­trial in­sects. It also eats cray­fish, mus­sels, squid, am­phib­ians, lizards, snakes, ro­dents, birds, eggs, car­rion, plant ma­te­ri­als, and garbage and refuse at land­fills. It is usu­ally a soli­tary for­ager, and it strongly de­fends its feed­ing ter­ri­tory. The night heron prefers to feed in shal­low wa­ters, where it grasps its prey with its bill in­stead of stab­bing it. A tech­nique called 'bill vi­brat­ing'--which is open­ing and clos­ing the bill rapidly in wa­ter--cre­ates a dis­tur­bance which may lure prey. Evening to early morn­ing are the usual times it feeds, but when food is in high de­mand, such as dur­ing the breed­ing sea­son, it will feed at any time of the day. (Davis, 1993)

Eco­nomic Im­por­tance for Hu­mans: Pos­i­tive

Black-crowned night herons have been hunted for food, though they are hunted for this pur­pose much less fre­quently now.

Eco­nomic Im­por­tance for Hu­mans: Neg­a­tive

At fish hatch­eries, hu­mans claimed that the amount of fish the birds were con­sum­ing were be­com­ing de­struc­tive. If they nest near human set­tle­ments, they are con­sid­ered pests. (Davis, 1993)

Con­ser­va­tion Sta­tus

In the late 1960s, de­clines in many black-crowned night heron pop­u­la­tions were noted, and were at­trib­uted to the use of DDT. The sta­tus of these pop­u­la­tions is in­dica­tive of en­vi­ron­men­tal qual­ity due to the high rank of these birds in the food chain, and their wide ge­o­graphic dis­tri­b­u­tion.

Adults were often killed or trapped near fish-cul­ture es­tab­lish­ments, due to their fishy diet, but other meth­ods of dis­cour­ag­ing them from eat­ing the fish are now avail­able. It is es­ti­mated that 1,300 birds were killed per year at fish hatch­eries in nine states. Herons that nested too close to human set­tle­ments were con­sid­ered pests and were also often killed, but other meth­ods that do not in­volve killing have been de­vel­oped. Since most pop­u­la­tions are sta­blized or in­creas­ing, man­age­ment has not been a major focus, though habi­tat de­struc­tion is an im­por­tant fac­tor in the con­ser­va­tion of this species. (Davis, 1993) This is a species of spe­cial con­cern in Michi­gan.

• IUCN Red List

  Least Concern
  More information

• IUCN Red List

  Least Concern
  More information

• US Migratory Bird Act

  Protected

• US Federal List

  No special status

• CITES

  No special status

• State of Michigan List

  Special Concern

Con­trib­u­tors

Ali­cia Ivory (au­thor), Uni­ver­sity of Michi­gan-Ann Arbor.

Ref­er­ences

Davis, W.E., Jr. 1993. Black-crowned Night-Heron (Nyc­ti­co­rax nyc­ti­co­rax). In The Birds of North Amer­ica, No. 74 (A. Poole and F. Gill, Eds.). Philadel­phia: The Acad­emy of Nat­ural Sci­ences; Wash­ing­ton, D.C.: The Amer­i­can Or­nithol­o­gists' Union.

http://​www.​mbr.​nbs.​gov/​id/​htmid/​h2020id.​html

http://​www.​biology.​ualberta.​ca/​uamz.​hp/​heron.​html