Grey heron

Name and taxonomy

Carl Linnaeus gave the grey heron its scientific name in 1758. The genus name Ardea is the Latin word for a heron, and cinerea means ash grey. Four subspecies are recognised, and each holds a different part of the range. They divide Europe and western Asia, eastern Asia, Madagascar and the coast of Mauritania. Some ornithologists treat the Mauritanian form, A. c. monicae, as a species of its own.

The order Pelecaniformes groups the herons with the pelicans, the ibises and the spoonbills. Within the heron family the bird belongs to the subfamily Ardeinae, the typical herons. In Ireland people often call it a crane, although true cranes sit in another family.

Evolution and relatives

The genus Ardea holds the great herons, the largest members of the family. The nearest lookalike is the great blue heron of North America, which is bigger. That bird carries chestnut brown flanks and thighs, and the grey heron does not. The cocoi heron of South America forms a superspecies with the grey heron. The three birds probably descend from one ancestor that spread and then split.

Grey herons sometimes pair with other species and produce hybrid young. Recorded partners include the great egret, the little egret and the purple heron. Hybrids with the great blue heron are known as well.

Appearance

A grey heron stands up to 100 cm tall, so a bird on a riverbank reaches an adult's chest. The back and the wings are ash grey, and the underparts are a paler greyish white. A broad black stripe starts at the eye and ends in a thin drooping crest. The front of the neck carries dark streaks, and black marks show along the flanks. The bill is long, straight and pinkish yellow, and it brightens in the breeding season. The eye is bright yellow, and the very long legs are brown.

Young birds look duller than their parents. Their head stripe is grey rather than black, and the crest stays small and dark. The wings are broad, and a span of 155 to 195 cm gives a slow, heavy flight. A flying heron folds its neck into an S and trails its legs behind the tail. That shape separates herons from cranes and storks, which fly with the neck straight.

Habitat and range

The grey heron breeds across most of the Palearctic region. In Norway the breeding range reaches 70 degrees north, further than anywhere else. To the south it takes in Spain, the Balkans, Iraq, Iran, India and Myanmar. African birds hold the land south of the Sahara, plus Morocco, Algeria and Tunisia. Separate subspecies occupy eastern Asia, Madagascar and the islands off Mauritania.

Almost any shallow water with fish in it can hold a heron. The bird uses lakes, rivers, marshes, ditches, flooded fields, estuaries and the open shore. It also hunts on pasture, and it has taken beetles and lizards in desert country. Colonies usually sit near feeding water, though a few stand eight kilometres away. A hunting bird may travel as far as 20 km from the nest. GBIF holds records from 188 countries, a total that includes strays and captive birds.

Diet and feeding

Fish make up most of what a grey heron eats. The bird also takes frogs, insects, crustaceans, water voles, rats, stoats and young rabbits. It kills ducklings, and a water rail is about the largest bird it can swallow. Prey runs from 1 cm fish weighing under a gram to carp of 30 cm and eels of 57 cm. Items over 100 grams are common for an adult, and some pass 500 g. One paper describes a heron that caught and swallowed a sea trout of 680 g.

The hunting method is patience. The bird stands motionless in the shallows, or waits on a rock beside the water. It can also wade slowly with the neck curved, then straighten it and stab. Small fish go down head first, in one gulp. Bigger prey is carried ashore, beaten on the ground and torn apart before it is eaten. The heron coughs up pellets of fur, bone and insect cases that it cannot digest.

Behaviour and social life

A grey heron feeds alone and guards the stretch of water it is using. It gathers with others only to breed and to roost. Adults spend long spells standing still on one leg. They perch in trees and also stride about on open ground. Dawn and dusk are the main hunting periods, but the bird feeds at any hour. Near dusk the birds climb into trees, probably because poor light hides an approaching predator.

Flight is slow, with deep wingbeats and short glides. Herons sometimes circle to a great height, though less often than storks do. In spring the birds chase each other above the colony and swoop towards the ground. Adults drive away young birds that come too close to an active nest. They stare at the intruder, raise the crest and stab forward with the head.

Some grey herons now live in towns. In the Netherlands the species has settled in cities over recent decades. Amsterdam birds visit street markets and snack bars, and a few accept food at doorsteps. Others wait beside anglers and take a share of the catch. Zoo herons steal fish put out for penguins, pelicans, otters and seals.

Communication and senses

The usual call is a loud croak, often written as frank. A colony is noisier, with a range of rough throaty sounds. A male advertises from his nest site to bring a female in. He uses a harsh schaah to push rival birds away from the nest. A soft gogogo signals unease, for example when a person walks below the trees. Chicks make a loud chattering or ticking noise.

Posture carries as many messages as sound does. A raised crest and a stabbing head mean threat. A bill pointed at the sky, with the wings spread, belongs to courtship. Sight guides the strike, and hunting is harder once the light goes. Like other herons, the bird also uses hearing and touch to find its food.

Reproduction and life cycle

Grey herons breed in colonies, and the colony site is called a heronry. Most sit high in tall trees near water. Reed beds, bramble patches, low bushes and cliff ledges also serve. A nest starts as a small platform of sticks and grows bulky as pairs add material. The male gathers the sticks and the female builds with them. Breeding runs from February to June over much of the range.

The male calls from his chosen site until a female joins him. The pair then perform a stretching display, lifting the neck and folding it back. In the snapping ceremony a bird drops its head and claps its mandibles together. That display may be repeated 20 to 40 times. The male offers a stick, the two birds preen each other, and mating follows.

A clutch holds three to five greenish blue eggs, and an egg averages 60 by 43 millimetres. Eggs arrive at two day intervals, and sitting starts after the first or the second one. Both parents incubate, and the eggs hatch after about 25 days. Chicks first take food from the side of an adult's bill. Later the parents drop food into the nest and the young fight over it. Chicks fly at seven to eight weeks and stay dependent until nine or ten weeks.

Most pairs raise one brood a year, and a second brood is rare. A bird can breed in the season after it hatches. A heron that survives its first winter lives about 5 years, and the record is 23.

Predators and threats

An adult grey heron carries a heavy bill and has few enemies. White-tailed eagles and golden eagles kill them, and goshawks do so more rarely. Foxes are named as the main predator in some accounts. Crows and kites lure the parents off the nest and then take eggs or chicks. One heron found dead in the Pyrenees was probably killed by an otter.

Winter is the biggest killer of young birds. About 67 per cent of first year herons die, and the rate falls sharply after that. A Czech study recorded 29 species of parasitic worm in central European herons. Young birds carried fewer species than adults, but heavier infections. Fish farmers shoot and poison herons, and pollution can thin the eggshells.

Population and conservation

The IUCN places the grey heron in the Least Concern category. Estimates put the adult world population between 790,000 and 3,700,000 birds. Numbers look stable across the range as a whole. iNaturalist holds 259,944 observations of the species, which shows how easy it is to find. The British list places it on the green list of conservation concern.

Regional assessments do not all agree with the global one. Lists for Israel and Palestine record the breeding bird as regionally extinct. German and Austrian lists call it threatened or close to it. People long treated the heron as a fish thief, and shooting was common. Legal protection probably explains much of the recovery in western Europe.

Colonies can still be destroyed. An Estonian colony of up to 125 nesting trees was protected in 1990. Every suitable tree there was felled in 2001, against the rules that covered the site. That loss started a national heron project. It mapped the colonies and feeding grounds of the whole country between 2007 and 2014.

Relationship with humans

The grey heron lives close to people over most of its range. Garden ponds stocked with ornamental fish draw herons, and young birds learn to hunt there. Fish farms lose stock to the birds, and herons can also spread fish diseases. Named examples are pancreatic necrosis, viral haemorrhagic septicaemia and spring viraemia of carp. Soviet work in the 1970s counted heavy losses of carp and mullet in Ukraine.

Other studies balance the account. German pond research found that herons remove many fish that carry a tapeworm disease. The birds eat large numbers of harmful insects as well. A big colony changes the soil below it, because droppings add nitrogen and phosphorus. One Russian study measured a soil pH near 4.5 under a colony fifteen years old.

People once ate herons in Britain, and roast heron was a dish for a great occasion. Guests at the installation of George Neville as Archbishop of York in 1465 ate 400 of them. Young birds were still shot for the table in Romney Marsh in 1896. Nobody farms or keeps the species today, and it has no market value.

In culture and myth

In ancient Egypt the deity Bennu appeared as a heron in New Kingdom art. Bennu stood for the sun, for creation and for rebirth. Egyptian texts call the bird self created and treat it as the soul of Ra. Herodotus later wrote of an Egyptian bird that lived 500 years. The Greek phoenix may take its name from Bennu, though the stories differ. Roman augurs listened to the call of a heron and read it as an omen.

Medieval British heraldry used the heron as a badge of patience and nobility. Writers of the period linked the still fishing bird with quiet thought. Four English surnames come from the bird: Earnshaw, Hernshaw, Herne and Heron. The ending shaw means a wood, so the names mark a place where herons nested. Two grey herons appear in a stained glass window at Selborne church in Hampshire. In the Maldives the bird is called Maakana, and a satirical television character carries the name.