Four subspecies of grey herons are recognized, each with relatively distinct geographic ranges: A. cinerea cinerea occurs in Europe, Africa, western Asia; A. cinerea firasa in Madagascar; A. cinerea jouyi in eastern Asia; and A. cinerea monicae on islands near Banc d'Arguin, Mauritania. Ardea cinerea monicae is considered by some to be a distinct species. (Arlott, 2009; Hancock, et al., 1984; Linegar and Renner, 2007)
Grey herons are very hardy and generally adapt well to new environments. However, for continuous habitation, grey heron populations require locations that experience at least four months of warm weather. These warmer periods are necessary for laying eggs and early development of chicks. Grey herons also require some type of shallow body of water, which they use as their primary forage sites. These bodies of water may include saltwater or brackish inlets and estuaries, freshwater rivers, streams, lakes, or marshes, and even aquacultures used in fish farming. Roosting requirements vary by geographic region; however, many individuals choose to roost in branches at or near the top of taller trees. If trees are unavailable, grey herons may roost in dense brush or undergrowth. (Hancock, et al., 1984; Peterson, et al., 1967)
Grey herons are comparable in size to great blue herons (Ardea herodias) of North America. Body length in grey herons typically ranges from 84 to 102 cm. Like all “great herons” (Ardea species), grey herons are fairly large birds. In contrast, other genera of herons (Family Ardeidae), such as pond herons (Ardeola species), rarely exceed average body lengths of 49 cm. Body weight of grey herons typically ranges from 0.226 to 1.36 kg. This species exhibits a distinct arched wing when flying, with a wingspan of 155 to 175 cm. (Dharmakumarsinhji, 1957; Hancock, et al., 1984; Mullarney, et al., 2009; Peterson, et al., 1967)
As their common name suggests, grey herons have predominantly grey plumage covering their wings, dorsum, and most of the neck. Subspecies Ardea cinerea monicae is distinguished by its lighter plumage and shorter crest. In all grey heron adults, the head is white with long black feathers that extend from the eyes to the beginning of the neck, forming a large, impressive crest. Juveniles retain a dark crown of grey feathers into their first winter, after which they begin to develop the white forehead and distinctive black crest typical of adults. Grey herons have yellow bills through most of the year, but these acquire an orange tint during the breeding season. As with other herons (Family Ardeidae), grey herons fly with their head pulled back toward the body while keeping their legs extended behind them. This body positioning during flight distinguishes herons from cranes (Family Gruidae), which fly with their neck extended. (Arlott, 2009; Hancock, et al., 1984; Mullarney, et al., 2009; Peterson, et al., 1967)
At the beginning of the breeding season, grey heron males select nesting sites. After choosing a suitable site, they make low grating calls to attract potential mates. Provided there are not multiple females approaching a single male, females choose a mate by approaching the males nesting site. Like great blue herons, both sexes must consent before pairing and mating occurs. Disinterested males often chase females from their nesting site to demonstrate their lack of interest. Once a male attracts a female to its nesting site, it begins a series courtship behaviors that include neck stretching, thrusting, and bowing. These lunging and bitterning displays, along with bill clapping, comprise most of the courtship dance performed by males to impress females. If the female remains at the site, the pair engages in mutual grooming behaviors called allopreening. At this point, the male and female have formed a monogamist pair that will remain together throughout the breeding season. (Hancock, et al., 1984; Milstein, et al., 1970; Mock, 1976)
The breeding season for grey herons begins as early as February and continues through May or early June. At the beginning of the breeding season, each male selects a nest site, most often situated in the branches of tall trees. Nests also have been reported in dense undergrowth and occasionally on bare ground. Grey heron nests are constructed from nearly any materials the male can gather; most often these materials include sticks and grasses. Once made, a nest will be used repeatedly from season to season, with subsequent nests built upon those of previous years. Larger, more developed nests are desirable and quickly taken, usually by older males. These are guarded fiercely until paring and copulation have occurred. (Hancock, et al., 1984; Milstein, et al., 1970)
Grey herons generally lay and raise one brood during the breeding season. However, if a brood is lost, it is not uncommon for herons to produce a replacement brood. Two broods from the same pair are considered a very rare occurrence, but have been recorded. Typically, females lay two to five eggs over a period of two or more days. Eggs are light blue-green in color. The number of eggs laid depends on the area in which the heron lives and the favorability of environmental factors; clutches as small as a single egg or as high as 10 eggs have been observed. Eggs typically take 25 to 26 days to incubate and hatch. Hatchlings compete with one another for food and parental care during early development, and commonly push one another from the nest. Hatchlings also have been reported to cannibalize deceased nest mates. Hatchlings fledge after approximately 50 days. However, despite leaving the nest, fledglings are not completely independent until 9 to 10 weeks. These offspring will be sexually mature by the following breeding season. (Hancock, et al., 1984; Milstein, et al., 1970)
Both male and female grey herons contribute to providing for and protecting their young. During nest building, most supplies are gathered by males. Construction of the nest is coordinated by females. Males aggressively defend females and unhatched eggs. Once hatched, both parents provide food to their offspring. Initially, young are fed directly. Later, parents regurgitate food onto the nest, where hatchlings must compete for food resources. Young remain with their parents for an extended period of time after they have fledged and are capable of leaving the nest. (Hancock, et al., 1984; Milstein, et al., 1970)
The average expected lifespan for grey herons is 5 years. Mortality is highest during the first year, at a rate of 67%. Mortality declines nearly 30% for the second year of life, and continues to fall as grey herons age. The oldest recorded age of a grey heron in the wild is 23 years, 9 months, and 2 days (more than four times their expected life span). (Mead, et al., 1979; Robinson, 2005)
Grey herons demonstrate differing behaviors as they mature. When they are born, early behaviors are dependent upon resource availability. Siblicide often occurs when food is in short supply. In these cases, nestlings show aggression toward one another, and sometimes the smallest or weakest offspring are killed. After the first year, immature grey herons (individuals less than two years old) may appear at breeding sites. When immature individuals arrive at a breeding site, they often are lured to the nests that show the most activity (e.g. breeding, feeding, and/or nest building). Adults typically respond with aggressive behavior towards the juvenile birds, causing them to flee. These adult aggressive behaviors involve looking directly towards the intruder, performing a stabbing motion with their head, and raising their crest. This aggressive behavior is believed to be associated with defense of their eggs and nest, since young become highly territorial when they feed. (Draulins and Vessem, 1986; Hancock, et al., 1984; Matsunaga, 2000; Owen, 1959; Pistorius, 2008; Sgadelis, 1997; Vessem and Draulans, 1986)
While grey herons are generally solitary birds, they gather during the breeding season to improve their chances of finding a mate. Their studies suggest that grey herons group breeding does not reduce predation risks or aid in locating foraging areas. Male courtship rituals begin with continuous advertising calls to attract females. Once females are in the vicinity, males stretch their wings and point their bills upwards. This differs from the downward bill position and lunging movements used to threaten intruding males. Males and females then touch bills numerous times and preen one another prior to mating. Once eggs hatch, both parents are responsible for feeding and caring for chicks. When the breeding season ends and chicks are able to fly, grey herons disperse (typically southwest). Depending on the region, some individuals may remain in the breeding area. (Draulins and Vessem, 1986; Hancock, et al., 1984; Matsunaga, 2000; Owen, 1959; Pistorius, 2008; Sgadelis, 1997; Vessem and Draulans, 1986)
Behaviors also are affected by weather and time of the day. For example, when it is colder, sleeping duration increases. During windy conditions, individuals rest more than they sleep. During the day, grey herons most often roost on the ground. However, near dusk, they begin to take cover in trees. This behavior is not limited to the breeding season but occurs year-round. It is believed that grey herons take cover in trees to escape predators, since their vision is hindered by lack of light. (Draulins and Vessem, 1986; Hancock, et al., 1984; Matsunaga, 2000; Owen, 1959; Pistorius, 2008; Sgadelis, 1997; Vessem and Draulans, 1986)
Hunting behaviors typically involve waiting for prey until they are within striking range. Comparisons between different environments (e.g. lakes versus marshes) showed little variation in hunting or foraging behaviors, other than strike rates and biomass intake. (Wet meadows had higher strike rates per capture but lower biomass intake). Tidal position also affects foraging behaviors; when tides are especially high (40+ cm), grey herons search for new feeding locations. (Draulins and Vessem, 1986; Hancock, et al., 1984; Matsunaga, 2000; Owen, 1959; Pistorius, 2008; Sgadelis, 1997; Vessem and Draulans, 1986)
Estimated breeding and resident home range area for grey herons is 99,700,000 square kilometers. Individual territory sizes are currently unknown for this species. (BirdLife International, 2011)
Grey herons, like many other bird species, show aggression through use of their neck. When a threat or a nuisance draws near, grey herons perform a stabbing motion with their head and raise their crest. Even though grey herons have been spotted in interspecific groups, including gulls (Family Laridae), they generally maintain a safe distance from individuals of other species. Since they are not social birds, they have little need for other communication behaviors except during the breeding season. During the breeding season, grey herons use advertising calls to attract females. They produce a harsh cry similar to other herons. They follow this by stretching their wings and pointing their bill upwards to initiate preening. Like most birds, grey herons perceive their environments through auditory, visual, tactile, and chemical stimuli. (Hancock, et al., 1984; MacGillivray, 1852; Owen, 1959)
Grey herons feed on a wide range of prey items but are primarily piscivores. In addition to fish (Class Actinopterygii), their diet consists of insects (Class Insecta), crustaceans (Subphylum Crustacea), frogs (Class Amphibia) and small mammals. They sometimes even ingest tiny birds. Recent studies have documented grey herons attempting to prey upon and consume white-throated rails (Dryomnas cuvieri aldabranus). This is the largest bird species upon which grey herons attempt to prey. While it is not clear how often grey herons succeed in feeding on rails, injuries have been noted after feeding attempts. (MacGillivray, 1852; Pistorius, 2008)
To locate food, grey herons wade through shallow water or move on land. They are thought to be most successful in capturing prey in the moonlight. Usually these herons stand still and wait for prey to approach in the water. They capture prey with their bills and generally swallow it whole, in one swift gulping action. Like other herons (Ardea species), grey herons in deeper water typically stand still on one foot and wait, sometimes for extended periods of time, for potential prey to swim near. (MacGillivray, 1852; Pistorius, 2008)
Foxes (Canidae, usually Vulpes species) are the primary predators of grey herons. Crows (Corvus species) may feed upon grey heron eggs, but typically only eggs that have already been abandoned. Human activities, particularly hunting, capturing, and polluting, often are responsible for grey heron mortality. (Draulins and Vessem, 1986; Hancock, et al., 1984; Mead, et al., 1979)
Grey herons are important in limiting fish populations in estuaries, rivers, and other bodies of water. Their nests also provide shelter for rodents and insects. (Milstein, et al., 1970)
Grey herons do not have any known economic benefits to humans.
Grey herons can have negative effects and potentially cause dramatic losses from fish farms, preying upon readily available fish and potentially spreading diseases through the farm. Grey herons can encourage the spread of common fish viruses and infectious diseases, such as pancreatic necrosis (IPN), viral haemorrhagic septicaemia (VHS), and spring viraemia of carp (SVC). Herons spread these diseases through regurgitated foods and excreted wastes. (Peters and Neukirch, 1986)
The conservation status for grey herons is listed as least concern. Grey herons are widely distributed and relatively abundant, with an estimated world-wide population between 790,000 and 3,700,000 adults. Overall population size appears to be stable. The biggest threats to grey herons in the future are shooting and poisoning by fish farmers. Potential pollution impacts include calcium issues, thinning of eggshells, reproductive problems, and suppressed immune systems. (BirdLife International, 2011; Hancock, et al., 1984; Mateo, 2006; Rose, 2006)
Justin Bower (author), Radford University, Daniel Rabago (author), Radford University, Christine Small (editor), Radford University, Rachelle Sterling (editor), Special Projects, Catherine Kent (editor), Special Projects.
living in sub-Saharan Africa (south of 30 degrees north) and Madagascar.
living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.
uses sound to communicate
young are born in a relatively underdeveloped state; they are unable to feed or care for themselves or locomote independently for a period of time after birth/hatching. In birds, naked and helpless after hatching.
having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.
a wetland area rich in accumulated plant material and with acidic soils surrounding a body of open water. Bogs have a flora dominated by sedges, heaths, and sphagnum.
areas with salty water, usually in coastal marshes and estuaries.
an animal that mainly eats meat
either directly causes, or indirectly transmits, a disease to a domestic animal
Found in coastal areas between 30 and 40 degrees latitude, in areas with a Mediterranean climate. Vegetation is dominated by stands of dense, spiny shrubs with tough (hard or waxy) evergreen leaves. May be maintained by periodic fire. In South America it includes the scrub ecotone between forest and paramo.
uses smells or other chemicals to communicate
the nearshore aquatic habitats near a coast, or shoreline.
active at dawn and dusk
animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.
an area where a freshwater river meets the ocean and tidal influences result in fluctuations in salinity.
parental care is carried out by females
forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.
offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).
parental care is carried out by males
marshes are wetland areas often dominated by grasses and reeds.
makes seasonal movements between breeding and wintering grounds
Having one mate at a time.
having the capacity to move from one place to another.
the area in which the animal is naturally found, the region in which it is endemic.
found in the oriental region of the world. In other words, India and southeast Asia.
reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.
an animal that mainly eats fish
Referring to something living or located adjacent to a waterbody (usually, but not always, a river or stream).
breeding is confined to a particular season
reproduction that includes combining the genetic contribution of two individuals, a male and a female
a wetland area that may be permanently or intermittently covered in water, often dominated by woody vegetation.
uses touch to communicate
that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).
Living on the ground.
defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement
the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.
A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.
A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.
A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.
uses sight to communicate
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