Nyctanassa violacea

Geographic Range

Yellow-crowned night-herons ( Nyctanassa violacea ) are small, semi-nocturnal wading birds that inhabit freshwater and coastal regions throughout North and South America, specifically the southeastern United States, Central America, and northern South America. In North America, their range has increased northward in recent decades and the species can now be found from southern New England, south to Florida, and west to Texas. Their range extends into the continent along the Mississippi and Minnesota Rivers. Further south, their range includes the coasts of Mexico and Central America, to northern Brazil and Peru. This species is also found on Caribbean islands like the Bahamas, Puerto Rico, Cuba, and the Lesser Antilles. Their breeding grounds are primarily located in the northern half of their United States range, in inland areas. Their wintering range is farther south in Central and South America and more coastal. Much of the research on this species has been conducted in the United States in coastal and inland habitats.

• Biogeographic Regions
• nearctic nearctic
  • native native
• neotropical neotropical
  • native native

Habitat

Yellow-crowned night-herons live in two major habitat types. Farther inland, this species is found in freshwater wetlands, wooded swamps, and marshes. They are also commonly found in freshwater lowlands and other areas that regularly flood. Along the coast, yellow-crowned night-herons inhabit brackish to saline thickets, lagoons, mangrove forests, and rocky, cliff-bound coasts. They have even been observed on dry islands in the Caribbean Sea, with little fresh water. Yellow-crowned night-herons are specific to these habitats because their diet consists mostly of aquatic prey. This species builds nests at a variety of heights, from a few meters above the water, to tree branches 12 m above the ground.

• Habitat Regions
• temperate temperate
• tropical tropical
• saltwater or marine saltwater or marine
• freshwater freshwater

• Terrestrial Biomes
• forest forest

• Aquatic Biomes
• lakes and ponds
• rivers and streams
• coastal coastal
• brackish water brackish water

• Wetlands
• marsh marsh
• swamp swamp

• Other Habitat Features
• riparian riparian
• estuarine estuarine

Physical Description

Yellow-crowned night-herons are medium-sized wading birds, weighing between 650 and 800 g. This species is about 55 to 70 cm in length, from the tip of their bill to the end of their tail, with a wingspan of 1.1 m. There are no major differences in the physical appearance of males and females, though males are slightly larger. Adult yellow-crowned night-herons have a slate-gray body with a black head, a white streak across both cheeks, and distinct yellowish crown and plumes. Their bill is black, broad, and stout. Their legs are orange-to-yellow, and their eyes are noticeably red. The feathers of their wings, mantle, and back have black centers and are edged in light gray; this gives the adult’s wings a scaled appearance. Immature yellow-crowned night-herons have distinctly different plumage from adults. Juvenile herons are grayish brown across their body and head, with fine white speckles throughout their body. They lack the yellow crown and plumes, but have the red eyes. Their bill and legs are black. Immature yellow-crowned night-herons are similar in appearance to juvenile black-crowned night-herons . These juveniles can be distinguished during flight. In flight, the feet and part of the legs of yellow-crowned night-herons extend beyond their tail, whereas the feet and legs are barely visible in black-crowned night-herons. Juvenile yellow-crowned night-herons slowly develop adult plumage after several years of molting.

• Other Physical Features
• endothermic endothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• sexes alike
• male larger

Reproduction

Yellow-crowned night-herons are a monogamous, pair-bonding species that nests either alone or in colonies of four to five nearby nests. When in colonies, pairs construct nests on separate trees. Pair formation occurs either during migration or early in the breeding season on the breeding range. The details of pair formation are unclear, though flight activities, stretch displays, and preening are more frequent early in the breeding season and may play some role in mate choice. Once a pair is formed, the male and female work together to build a nest, but play different roles. The male typically collects materials for the nest and the female remains at the nest site and builds the nest. There is great variety in nest substrate and location. Both of these factors depend on the habitat, freshwater, brackish, or saltwater, and on more variable conditions like the flood regime. A typical nest consists of a platform of sticks with a lining of leaves or needles. In freshwater habitats, oak branches and pine needles are the most common materials used to build nests, though mangrove materials are often used in brackish conditions. Nest locations vary even more than nest materials, but there are two main trends. Herons breeding farther inland in freshwater habitats tend to nest in the upper reaches of the canopy, away from the center of the tree. In coastal regions, the nests are typically closer to the surface of the water, possibly due to a scarcity of high trees. Low nests are particularly common in mangrove swamps.

• Mating System
• monogamous monogamous

Once the nest is complete, the full spectrum of yellow-crowned night-herons' reproductive behaviors are revealed. The first set of reproductive behaviors occurs during pair formation and nest construction and includes flight activities and stretch displays. Flight activities involve in-flight behaviors like pursuit, circle flight, and exaggerated wing flapping, used to alert mates and other colony members to breeding activities, like nest construction and egg laying. Stretch displays involve a rapid up and down extension of the neck, with the head and bill kept horizontal. These displays are used to synchronize nest construction and activities between mates. Once the nest is complete and egg laying begins, the greeting ceremony signifies a mate returning to the nest, oftentimes for copulation or nest relief. In this display, the returning bird quickly raises and lowers the plumes of the crest and scapulae and gives a soft “yup, yup” call. Yellow-crowned night-herons breed once a year, from early spring to early summer. Pair bonding and nesting occurs from early March to April and the eggs hatch after two to three weeks of incubation. Yellow-crowned night-herons are a single brood species and usually lay three to five oval, pale blue-green eggs. If the nest is lost early in the breeding season, a second brood may occur. After hatching, the chicks grow rapidly for five weeks and fledge in about their sixth to eighth week. Even after fledging, the juveniles often remain tied to the nest for a couple more weeks, receiving food from the parents and learning how to forage through observation. Thus, the complete breeding season can end as late as July, when the juveniles have grown and learned enough to survive on their own.

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

Parental investment is very high in this species. Both the male and female are heavily involved in offspring care from the period of nest construction through post-fledging learning. The parents build and defend the nest together, with the male collecting materials and the female constructing the nest. After egg laying begins, both sexes incubate the eggs in the same position: head retracted and eyes closed. A parent places one foot on either side of the eggs, lowers its body on top, and fidgets until it has reached this position. When the eggs hatch, both parents participate in feeding the altricial young. One parent typically leaves the nest to forage and then regurgitates digested food into the nest for the young to eat. Throughout nest construction and offspring care, both the male and female use aggressive forward displays to defend the nest and their young against intruders and extra-pair conspecifics. The defending individual either stands still or walks toward the intruder while thrusting their head forward and vocalizing or snapping their bill. Another defensive reproductive behavior occurs when both parents are at the nest. When eggs or young are present, the adults face in opposite directions almost 75% of the time they are together at the nest. This is most likely a mechanism to improve vigilance in a colonial nesting situation, where the threats of predation and extra-pair copulations are high. As the nestlings age, they begin to use feeding displays to alert the parents of their hunger. With time, the nestlings are slowly able to lift their heads, stand, walk, and eventually flap their wings and fly. However, even when the juveniles fledge about six to eight weeks after hatching, they return to the nest for a couple more weeks for food. During this interval, juveniles learn important skills from their parents, in particular the ability to forage more efficiently. In this way, adult yellow-crowned night-herons exhibit intense parental care throughout all stages of juvenile development.

• Parental Investment
• altricial altricial
• male parental care male parental care
• female parental care female parental care
• pre-fertilization
  • provisioning
  • protecting
    • male
    • female
• pre-hatching/birth
  • provisioning
    • male
    • female
  • protecting
    • male
    • female
• pre-weaning/fledging
  • provisioning
    • male
    • female
  • protecting
    • male
    • female
• pre-independence
  • provisioning
    • male
    • female
  • protecting
    • male
    • female
• post-independence association with parents
• extended period of juvenile learning

Lifespan/Longevity

There is little information available regarding the lifespan of yellow-crowned night-herons in the wild or in captivity. However, the transition from juvenile to adult plumage takes about two years. Banding stations in the United States have records of a banded individual that was six years and three months old when collected. From this evidence, yellow-crowned night-herons must have the ability to live at least four to six years, but studies tracking individual birds must be conducted in order to determine the average and maximum lifespan of the species.

Behavior

Outside of reproduction, the behavior of yellow-crowned night-herons can be split into two categories: general and foraging. When not foraging, adult herons walk slowly through the shallow waters of wetlands, swamps, and coastal thickets and rarely enter deep waters. In flight, the feet and legs of yellow-crowned night-herons are visible beyond the end of the tail and they flap their wings slowly. Preening is a common and important behavior for this species. Adults preen themselves and one another, particularly after foraging. Foraging behavior involves a slow, stalking motion as night-herons search for prey in the shallow water. Upon finding prey, individuals strike quickly and use their wide, stout beak to crush the organism in their mouth. Larger prey items tend to be handled longer, but dropped more often. Although they live in colonies, they typically forage alone. A large group of herons in one area may indicate an abundant food source. Adults and juveniles spend roughly the same amount of time doing general and foraging behaviors. However, adults are more efficient foragers than juveniles, who learn from the adults by observation.

• Key Behaviors
• arboreal arboreal
• flies
• diurnal diurnal
• nocturnal nocturnal
• motile motile
• migratory migratory
• colonial colonial

Home Range

During the breeding season, adults maintain and protect territories that are at least as large as the nest and nearby area. While breeding, adults have been observed foraging as far as 15 to 20 meters from the nest. There is little information about the range and territories of the species during migration and wintering.

Communication and Perception

Yellow-crowned night-herons communicate with conspecifics and other species via visual, tactile, and acoustic channels. Visually, herons use physical displays mostly for reproduction and occasionally for nest defense. Reproductive displays include a greeting ceremony when approaching the nest and a stretch display used during nest construction. The forward display is used to defend the nest against intruders. Tactile communication occurs frequently between adults and juveniles, starting with the incubation of the eggs. Adults feed the young in the nest by regurgitating food. Between adults, tactile communication takes the form of preening, feather ruffling, head scratching, and bill clappering. Acoustically, adult yellow-crowned night-herons have six major types of calls. The most common call is the “scaup” call, which is a loud, high-pitched quawk sound. It is usually used when a yellow-crowned night-heron is startled or leaving the colony. There are three calls linked to breeding: the “whoop” call during a stretch display, the “huh” call during pair formation, and the “yup, yup” call during the greeting ceremony. The “ahhh, ahhh” call is more aggressive and used when an intruder enters the nest area. The “squawk” call and the “bill snap” are also aggressive and used for the forward display.

• Communication Channels
• visual visual
• tactile tactile
• acoustic acoustic

• Perception Channels
• visual visual
• tactile tactile
• acoustic acoustic
• chemical chemical

Food Habits

Yellow-crowned night-herons eat mostly aquatic prey. They are considered crustacean specialists and over 80% of their diet consists of crayfish and crabs, particularly fiddler crabs, marsh crabs, and green crabs. Their wide, stout beak is well adapted for crushing crustacean exoskeletons. Inland herons eat primarily crayfish and coastal herons consume mostly crabs. The other 20% of their diet includes a wide variety of aquatic and terrestrial organisms. In terms of aquatic prey, yellow-crowned night-herons eat mussels, snails, aquatic worms and insects, leeches, amphibians (both frogs and tadpoles), and small fish such as eels and pipefish. The species also hunts an array of terrestrial organisms, including lizards, snakes, small mammals, and young birds that fall out of their nest. Yellow-crowned night-herons do not exclusively hunt during the night and have been observed foraging at all hours of the day. They forage alone by walking slowly through the wetland or coastal thicket and stalking for prey in the water. The herons typically select prey visually and at least partly by size. They spend longer amounts of time handling larger prey and are more likely to drop these bigger prey items. There are differences in foraging success between adults and juveniles and between different social situations. Juveniles tend to have a more diverse diet and are less efficient at prey capture than adults. This is particularly true when food is abundant and the herons forage in flocks. In these group settings, the efficiency of the juveniles is even lower because they are outcompeted by the adults.

• Primary Diet
• carnivore carnivore
  • eats non-insect arthropods

• Animal Foods
• birds
• mammals
• amphibians
• reptiles
• fish
• insects
• terrestrial non-insect arthropods
• mollusks
• aquatic crustaceans

Predation

Adult yellow-crowned night-herons have no direct predators, but humans hunt them for game and food on occasion. American crows frequently take and eat yellow-crowned night-heron eggs from nests.

Ecosystem Roles

The major and most obvious ecosystem role of yellow-crowned night-herons is as a predator. Yellow-crowned night-herons prey on a wide variety of organisms including crayfish, crabs, small fish, snakes, insects, lizards, young birds, and small mammals. However, they generally specialize in crustacean prey and have the biggest impact on crab and crayfish communities. Outside of human predation, this species is not typically prey itself. In addition, their freshwater and brackish niches are particular enough that they rarely face competition from other predators such as scarlet ibis . Outside of predation, yellow-crowned night-herons are an intermediate host of the eastern equine encephalomyelitis (EEE) virus and partly responsible for its amplification in mosquito populations.

Economic Importance for Humans: Positive

Outside of game hunting, yellow-crowned night-herons have no major positive effects on humans.

• Positive Impacts
• food food

Economic Importance for Humans: Negative

Like any large bird, yellow-crowned night-herons are capable of biting, but they rarely exhibit such aggressive behavior against humans. Typically, yellow-crowned night-herons sneak quietly away from human activity and return when the area is undisturbed. The greater potential threat from this species is disease transmission. Yellow-crowned night-herons are an intermediate host and amplifier of the eastern equine encephalomyelitis (EEE) virus, or sleeping sickness, which is common in the southeastern United States. Yellow-crowned night-herons first receive the virus from mosquitoes. In the avian host, the virus can be transmitted to a wider range of mosquito species that then transmit the virus to horses and humans, which are dead end hosts. Because the EEE virus causes mortality in horses and seizures or death in humans, the presence of yellow-crowned night-herons can have a potential negative effect on humans by transmitting and amplifying the virus.

• Negative Impacts
• injures humans
  • bites or stings
  • carries human disease

Conservation Status

There are several reports of yellow-crowned night-herons being killed for food by the Creoles of southern Louisiana and the inhabitants of the Bahamas. Today the species is occasionally hunted as a game bird. However, none of this hunting has caused a severe threat to its population. In fact, their breeding range has been expanding northward in recent decades.

Other Comments

Yellow-crowned night-herons were formerly classified in Nycticorax , the genus of black-crowned night-herons , under the name Nycticorax violacea .

Additional Links

Encyclopedia of Life

BioKIDS Critter Catalog

Contributors

Frank Stabile (author), The College of New Jersey, Keith Pecor (editor), The College of New Jersey, Leila Siciliano Martina (editor), Texas State University.

References

Afkhami, M., J. Strassmann. 2007. Adult yellow-crowned night-herons face in opposite directions at the nest. The Wilson Journal of Ornithology , 119: 747-749.

Audubon, J. 1937. The Birds of America . New York: The Macmillian Company.

Bagley, F., G. Grau. 1979. Aspects of the yellow-crowned night-heron reproductive behavior. Proceedings of the Colonial Waterbird Group , 3: 165-175.

Bent, A. 1963. Life Histories of North American Marsh Birds . New York: Dover Publications.

Bird Banding Laboratory, 2013. "Yellow-crowned night-heron" (On-line). United States Geological Survey. Accessed October 23, 2013 at https://www.pwrc.usgs.gov/BBL/longevity/Longevity_main.cfm .

Bull, J., J. Farrand. 1994. National Audubon Society Field Guide to Birds: Eastern Region . New York: Chanticleer Press.

Hassan, H., E. Cupp, G. Hill, C. Katholi, K. Klingler, T. Unnasch. 2003. Avian host preference by vectors of eastern equine encephalomyelitis virus. American Journal of Tropical Medicine and Hygiene , 69: 641-647.

Laubhan, M., F. Reid. 1991. Characteristics of the yellow-crowned night-heron nests in lowland hardwood forests of Missouri. Wilson Bulletin , 101: 486-491.

Laubhan, M., D. Rundle, B. Swartz, F. Reid. 1991. Diurnal activity and foraging success of yellow-crowned night-herons in seasonally flooded wetlands. Wilson Bulletin , 103: 272-277.

Martínez, C. 2004. Food and niche overlap of the scarlet ibis and the yellow-crowned night-heron in a tropical mangrove. Waterbirds , 27: 1-8.

Riegner, M. 1982. The diet of yellow-crowned night-herons in the eastern and southern United States. Colonial Waterbirds , 5: 173-176.

Watts, B. 2011. "Yellow-crowned Night-heron ( Nyctanassa violacea )" (On-line). The Birds of North America Online. Accessed October 23, 2013 at http://bna.birds.cornell.edu/bna/species/161 .