Grey herons are predominantly grey. Adults have white heads with long black feathers extending from the eyes to the neck, in the form of a large, impressive crest. Young birds have a crown of grey feathers up until their first winter, then they start to develop the adult's white forehead and black crest. They have yellow bills for most of the year, gaining an orange tint in the breeding season. In flight these herons pull their head into their body while stretching their legs out behind them.
The Grey heron is fairly common in most parts of Europe, Asia, and Africa. The northern dwellers migrate south during hard winters. It may reside in several types of habitats with either shallow fresh, salt, or brackish water. It can be found in open regions but requires trees for nesting. It can often be seen near rivers, marshes, lakes, and rice fields. On the coast, it is found in estuaries, tidal mudflats, and mangroves.
Grey herons are social birds; they may feed alone or in groups and at night they roost in trees or on cliffs and tend to be gregarious. During the breeding season, they nest in big colonies. Grey herons are diurnal, and during the day, they often perch in trees, but spend much time on the ground, striding about or standing still for long periods with an upright stance, often on a single leg. Near dusk, they take cover in trees. Weather and the time of the day can affect their behavior. For example, in colder weather, they will sleep for longer. In windy conditions, the rest rather than sleep. The main call of Grey herons is a loud croaking "fraaank", but a variety of guttural and raucous noises is heard at the breeding colony. A loud, harsh "schaah" is used by the male in driving other birds from the vicinity of the nest and a soft "gogogo" expresses anxiety, as when a predator is nearby or a human walks past the colony. The chicks utter loud chattering or ticking noises.
Grey herons are carnivores (piscivores) and feed mostly on fish. However, depending on the season and what is available, they also may eat amphibians, crustaceans, aquatic invertebrates, mollusks, snakes, small birds and rodents, and sometimes some plants.
Grey herons are monogamous. They stay together for the breeding season, which extends from early February until May or early June. Each male will select a nest site at the beginning of the breeding season, most often in a tall tree. Females lay 1 to 10 eggs, laying every two days. Both parents incubate the eggs, for a period of 25-26 days. They take turns four times each day, after the same display. Chicks are fed by both parents, who look after them attentively, one of them staying at the nest for the first 20 days. Feeding is through regurgitation into the mouth. They can fly at about 50 days old, remaining for 10 to 20 more days more at the nest.
Grey herons are hunted and trapped by people. They are threatened by changes in their habitat, including deforestation and the drainage of wetlands.
Grey herons have a wide distribution and are relatively abundant; the estimated world population of adults being between 790,000 and 3,700,000 individuals, including 223,000-391,000 breeding pairs in Europe, c.100,000-1 million breeding pairs in China, c.100-10,000 breeding pairs in Korea; c.100,000-1 million breeding pairs in Japan and c.100,000-1 million breeding pairs in Russia. The overall population size seems to be stable.
Grey herons are important for controlling fish populations in rivers, estuaries, and further bodies of water. Their nests provide shelter for insects and rodents.