Grey herons are about the same size as great blue herons, which are found in North America. Their feathers are mostly gray on their wings, body, and neck. Their heads are white and have long black feathers stretching from their eyes to the start of their neck. This means their head has a large and noticeable group of feathers called a crest. Young grey herons have a grey feathers on top of their head into their first winter. Afterwards, they get the white forehead and black crest like adult haves. Grey herons have yellow bills during most of the year, but they turn a little bit orange during the breeding season. Like all great herons, they are fairly large, even compared to other herons. Their bodies are 84 to 102 cm long and they weigh 0.226 to 1.36 kg. Their wingspan is 155 to 175 cm. Herons and cranes look very similar, but herons fly with their head pulled back toward the body, and cranes fly with their neck stuck out forward. (Arlott, 2009; Dharmakumarsinhji, 1957; Hancock, et al., 1984; Mullarney, et al., 2009; Peterson, et al., 1967)
Grey herons, also called common herons, live in a very large area. They are found throughout Eurasia and Africa, in places that have at least 4 months of warm weather. They are also found in North America, Greenland, and Australia. Scientists usually think that these other areas are outside their natural range. Some grey herons migrate, but the area where they live does not change too much between winter and summer. (Arlott, 2009; Hancock, et al., 1984; Linegar and Renner, 2007)
Grey herons are can easily adapt to different kinds of environments. They live year-round in places that have at least 4 months of warm weather. When it's warm outside, they lay eggs and their chicks develop. Grey herons live near shallow bodies of water, where they find food. This could be places where rivers meet the ocean, areas with standing water, freshwater rivers, streams, lakes, or marshes, and even fish farms. They usually rest or sleep in branches at or near the tops of taller trees. If this isn't possible, they rest or sleep in thick shrubs or undergrowth. (Hancock, et al., 1984; Peterson, et al., 1967)
When the breeding season starts, grey heron males pick out places to nest. When they find a good spot, they make low calls to attract females that are a grating sound. Females usually choose mates by approaching the nesting spot. If males aren't interested, they chase females away. They perform courtship rituals including stretching their necks, thrusting, and bowing. Males lunge and clap their bills to impress females. If the female stays, they groom each other's feathers, and become a pair for the rest of the season. (Hancock, et al., 1984; Milstein, et al., 1970; Mock, 1976)
Grey herons begin to breed as early as February and continue through May or early June. First, males find a spot for the nest, which is usually in the branches of tall trees. Other times, nests are in low-growing plants or even on bare ground. They are made of anything males can find, but usually sticks and grasses. Nests are used year after year, and often built up from one year to the next. Bigger nests are the most desirable and are quickly claimed by older males. Males guard their nests fiercely until after mating pairs are settled. (Hancock, et al., 1984; Milstein, et al., 1970)
Grey herons usually lay one set of eggs and raise one set of chicks. If something happens and the chicks are lost, they may lay another set of eggs. Females lay 2 to 5 blue-green eggs, which takes 2 or more days. The number of eggs the they lay depends on where they live and also their environment. They can lay anywhere from 1 to 10 eggs. In 25 to 26 days, the eggs hatch. Chicks compete with each other for food and parental care during early development. They even push each other out of the nest, and eat other chicks if they die. In about 50 days, the chicks can fly, but the take 9 to 10 weeks to become independent from their parents. During the next breeding season, they can have their own young. (Hancock, et al., 1984; Milstein, et al., 1970)
Both male and female grey herons help feed and protect the young. Males find most of the building materials for the nest, but females coordinate the building. Males aggressively defend females and their eggs. After the eggs hatch, both parents bring them food. At first, they feed the young directly. Later, they spit up undigested food onto the nest, and hatchlings compete to eat it. The young grey herons stay with their parents for quite a while, even after they are able to fly and leave the nest. (Hancock, et al., 1984; Milstein, et al., 1970)
Grey herons usually live about 5 years. About 67% of them actually die within the first year. The record for the oldest grey heron is 23 years, 9 months, and 2 days, which is four times older than their expected lifespan. (Mead, et al., 1979; Robinson, 2005)
Grey herons are usually found by themselves, but get together in groups during the breeding season to find a mate. They usually head southwest after the breeding season is over. Their day-to-day behavior depends partly on the weather and the time of day. They sleep longer when it's colder, and rest more than sleep when it's windy. In the daytime, they rest on the ground, but as it gets dark, they rest in trees. This resting in trees may help them escape predators, because they're harder to see. (Draulins and Vessem, 1986; Hancock, et al., 1984; Matsunaga, 2000; Owen, 1959; Pistorius, 2008; Sgadelis, 1997; Vessem and Draulans, 1986)
Grey herons usually hunt by waiting until prey are close enough to strike. They have pretty similar hunting behavior, whether they are hunting in a marsh or a lake. They tend to avoid hunting at really high tide. (Draulins and Vessem, 1986; Hancock, et al., 1984; Matsunaga, 2000; Owen, 1959; Pistorius, 2008; Sgadelis, 1997; Vessem and Draulans, 1986)
Grey herons can be aggressive with each other in certain situations. When they are born, they can get aggressive if there isn't much food around, and even kill their weaker siblings. Older adults also get aggressive toward younger grey herons that come near their nest during breeding. They make a stabbing motion with their head and raise up the feathers on the top of their head. This usually makes the younger birds flee. (Draulins and Vessem, 1986; Hancock, et al., 1984; Matsunaga, 2000; Owen, 1959; Pistorius, 2008; Sgadelis, 1997; Vessem and Draulans, 1986)
The total area where all grey herons live is estimated to be 99,700,000 square kilometers. (BirdLife International, 2011)
Grey herons communicate mostly by using body language and calls. Like many other birds. they use their neck to show aggression. They will stab with their head and raise the feathers on top of their head if a threat or bothersome other animal comes close. Grey herons are sometimes found together with some kinds of gulls, but more often stay away from other kinds of animals. Most of their communication happens during the breeding season because they aren't very social. In the breeding season, males make advertising calls to attract females. Their cry is harsh, like other herons. Then, they stretch their wings and point their bill upwards to initiate preening. Like most birds, their important senses are hearing, sight, touch, and chemical signals. (Hancock, et al., 1984; MacGillivray, 1852; Owen, 1959)
Grey herons eat many kinds of animals, but they mostly eat fish. They also eat insects, crustaceans, frogs and small mammals. They sometimes even eat tiny birds. They biggest birds they have been seen trying to eat are white-throated rails. Scientists don't know if they eat them successfully, but have watched grey herons injure them while trying. (MacGillivray, 1852; Pistorius, 2008)
Foxes are the most common predators of grey herons. Crows like carrion crows might eat their eggs, but usually this only happens if the eggs that have already been abandoned. Human activities like hunting, capturing, and dumping pollution often kill them. (Draulins and Vessem, 1986; Hancock, et al., 1984; Mead, et al., 1979)
Grey herons can have negative impact on fish farms, because they eat the fish and might also spread disease. Grey herons can spread viruses and infections like pancreatic necrosis (IPN), viral haemorrhagic septicaemia (VHS), and spring viraemia of carp (SVC). (Peters and Neukirch, 1986)
Grey herons do not have any known economic benefits to humans.
Grey herons live in a large area and are pretty common, so they are listed as "least concern" by the IUCN Red List. There are about 790,000 to 3,700,000 adult grey herons in the world. Their biggest threats are shooting and poisoning by fish farmers. They could also be in danger from pollution, which could cause problems with calcium, thin eggshells, problems with reproducing, and weakened 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.
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