European herring gull

Appearance

The male European herring gull is 60–67 cm long and weighs 1,050–1,525 g, while the female is 55–62 cm and weighs 710–1,100 g. The wingspan can range from 125 to 155 cm. Among standard measurements, the wing chord is 38 to 48 cm, the bill is 4.4 to 6.5 cm and the tarsus is 5.3 to 7.5 cm. Adults in breeding plumage have a light grey back and upper wings and white head and underparts. The wingtips are black with white spots known as "mirrors". The bill is yellow with a red spot and a ring of bare yellow skin is seen around the pale eye. The legs are normally pink at all ages, but can be yellowish, particularly in the Baltic population, which was formerly regarded as a separate subspecies ""L. a. omissus"". Non-breeding adults have brown streaks on their heads and necks. Male and female plumage are identical at all stages of development, but adult males are often larger.

Juvenile and first-winter birds are mainly brown with darker streaks and have a dark bill and eyes. Second-winter birds have a whiter head and underparts with less streaking and the back is grey. Third-winter individuals are similar to adults, but retain some of the features of immature birds such as brown feathers in the wings and dark markings on the bill. The European herring gull attains adult plumage and reaches sexual maturity at an average age of four years.

Distribution

Ireland: Copeland Bird Observatory, Co Down.

Britain: Since 2009, herring gulls in the United Kingdom have been on the red list of birds of conservation concern, including County Durham.

Europe: Recorded from all the coasts of Europe including the Mediterranean and occasionally inland.

Behavior

European herring gull flocks have a loose pecking order, based on size, aggressiveness, and physical strength. Adult males are usually dominant over females and juveniles in feeding and boundary disputes, while adult females are typically dominant when selecting their nesting sites. Communication between these birds is complex and highly developed —employing both calls and body language. The warning sounds to chicks are the most obvious to interpret.

The warning to their chicks sounds almost like a bark from a small dog. If the danger closes in, the bark is repeated, and when very close, the warning is three quick barks. If a chick is "grounded", the bird makes itself appear bigger to intimidate the threat. If other adult birds are present, they will help in the same way. For instance, a person with a dog may be attacked by many adult birds, even if just one chick is in danger.

The warning sound from a flying bird to a flock of fully fledged birds sounds very different. All kinds of gulls seemingly understand the "general alert warning sound" of all other gulls. Little doubt remains that the gull's screaming is a language for communication. It is limited to the present tense, but includes rather complex matters such as "follow me".

Two identical vocalizations can have very different meanings. For example, it depends on the position of the head, body, wings, and tail relative to each other and the ground.

Unlike many flocking birds, European herring gulls do not engage in social grooming and keep physical contact between individuals to a minimum. Outside the male/female and parent/chick relationships, each gull attempts to maintain a respectful 'safe distance' from others of its kind. However, the bird must be considered a social bird that dislikes being alone, and fights mainly occur over food or to protect their eggs and chicks. If a few birds discover a piece of food, the first one to land by the food piece often unfolds its wings to proclaim "this food is mine". This is very often opposed by another gull, and during a short fight, a third bird may grab the food while the two other are arguing. However, if much food is found, especially at a "dangerous location", the bird that discovered the food will call to other gulls close by. The first bird may dare to land, but waits before eating; the others then feel safe to land, and they eat. If a large feast is found at a safer location, the gull that discovers it calls to other gulls, but starts eating immediately. The conclusion is that if more food is available than one bird can eat, it shares the food with other gulls.

During the winter, large flocks can be seen at fields, especially if the ground has a high degree of moisture. At first sight, it the birds appear to be just standing there, but then on closer inspection, only their bodies are not moving; the birds actually are trampling the soil, most likely to trick worms to crawl closer to the surface of the soil.

During early spring and late autumn, many herring gulls feed heavily on earthworms, but they are very opportunistic birds that seem to have many sources of food. For instance in southern Scandinavia and northern Germany, this species recently has become the most common of all gulls, and the increase has mostly occurred in urban or suburban environments.

The great black-backed gull was around 1900 as common as the herring gull in the mentioned parts, but has not increased as much, though some signs indicate the bigger gull has learned some of the herring gull's behaviour within urban environments. Where the herring gull is breeding in coastal urban environments, the great black-backed gull seems to do the same, but in a lesser scale.

Herring gulls are good at producing all three eggs into flying birds. This means that at least one of the newly flying chicks loses both its parents within days after first flight. Some of these can later be seen in flocks of smaller gulls like the black-headed gull or the common gull. They are probably not welcomed in such flocks, but follow them for some months, anyway, and do thereby learn where to find food. Lonely juvenile herring gulls born in urban environments can also be seen staying for a some weeks close to outdoor restaurants and similar facilities, squeaking and begging for food from humans. By November or December, most juveniles have found other "flockmates", usually in areas near water.

The herring gull does not need swimming, but seems to enjoy all kind of waters, especially on hot summer days. It can only catch slow creatures, like small crabs, which it often drops from some altitude to crack them open. The bird has little real power in its jaws while biting, but it may "stab" with better strength. Fish on land, eggs of other birds, and helpless chicks of smaller ducks are about as much predator the bird gets. It is then far more successful as a scavenger. Like vultures, an adult bird can dig its whole head and neck into a dead rabbit, for instance. Although not always appreciated by mankind due to their droppings and screaming, the herring gull must be regarded as a "natural cleaner", and just as with crows, they help by keeping rats away from the surface in urban environment, not by killing rats, but by eating the potential rat food before the rats get the chance. Unlike real scavengers, herring gulls also eat most other things than meat, like wasted food of all kinds, from bread to human vomit. They seldom eat fresh fruit, but windfalls and rotten fruit seem more desired.

In cities, herring gulls have been witnessed attacking and killing feral pigeons.

The European herring gull has long been believed to have extremely keen vision in daylight and night vision equal or superior to that of humans; however, this species is also capable of seeing ultraviolet light. This gull also appears to have excellent hearing and a sense of taste that is particularly responsive to salt and acidity.

Parasites of European herring gulls include the fluke "Microphallus piriformes".

Reproduction

When forming a pair bond, the hen approaches the cock on his territory with a hunched, submissive posture, while making begging calls. If the cock chooses not to attack her and drive her away, he responds by assuming an upright posture and making a mewing call. This is followed by a period of synchronised head-tossing movements, after which the cock then regurgitates some food for his prospective mate. If this is accepted, copulation follows. A nesting site is then chosen by both birds which is returned to in successive years. European herring gulls are almost exclusively sexually monogamous and may pair up for life, provided the couple is successful in hatching their eggs.

Two to four eggs, usually three, are laid on the ground or cliff ledges in colonies, and are defended vigorously by this large gull. The eggs are usually olive-brown in colour with dark speckles or blotches. They are incubated by both parents for 28–30 days. The chicks hatch with their eyes open, covered with fluffy down, and they are able to walk around within hours. Breeding colonies are preyed upon by great black-backed gulls, harriers, corvids and herons.

Juveniles use their beaks to peck at the red spot on the beaks of adults to indicate hunger. Parents then typically disgorge food for their offspring. The young birds are able to fly 35–40 days after hatching and fledge at five or six weeks of age. Chicks are generally fed by their parents until they are 11–12 weeks old, but the feeding may continue for more than six months of age if the young gulls continue to beg. The male feeds the chick more often than the female before fledging, with the female more often feeding after fledging.

Like most gulls, European herring gulls are long-lived, with a maximum age of 49 years recorded. Raptors and seals occasionally prey on the non-nesting adults.

Food

These are omnivores and opportunists like most "Larus" gulls, and scavenge from garbage dumps, landfill sites, and sewage outflows, with refuse comprising up to half of the bird's diet. It also steals the eggs and young of other birds, as well as seeking suitable small prey in fields, on the coast or in urban areas, or robbing plovers or lapwings of their catches. European herring gulls may also dive from the surface of the water or engage in plunge diving in the pursuit of aquatic prey, though they are typically unable to reach depths greater than 1–2 m due to their natural buoyancy. Despite their name, they have no special preference for herrings — in fact, examinations have shown that echinoderms and crustaceans comprised a greater portion of these gulls' stomach contents than fish, although fish is the principal element of regurgitations for nestlings. European herring gulls can frequently be seen to drop shelled prey from a height to break the shell. In addition, the European herring gull has been observed using pieces of bread as bait with which to catch goldfish. Vegetable matter, such as roots, tubers, seeds, grains, nuts, and fruit, is also taken to an extent. Captive European herring gulls typically show aversion to spoiled meat or heavily salted food, unless they are very hungry. The gulls may also rinse food items in water in an attempt to clean them or render them more palatable before swallowing.

European herring gulls may be observed rhythmically drumming their feet upon the ground for prolonged periods of time in a behaviour that superficially resembles Irish stepdancing, for the purpose of creating vibrations in the soil, driving earthworms to the surface, which are then consumed by the gull. These vibrations are thought to mimic those of digging moles, eliciting a surface-escape behaviour from the earthworm, beneficial in encounters with this particular predator, which the European herring gull then exploits to its own benefit in a similar manner to human worm charmers.

Whilst the European herring gull is fully capable of consuming seawater, using specialized glands located above the eyes to remove excess salt from the body, it drinks fresh water in preference, if available.

The opportunistic diet of the herring gull has consequences for egg traits. A study found that larger eggs were laid in colonies where females consumed either a higher proportion of marine resources or terrestrial resources; smaller eggs were laid in colonies where females had an intermediate diet. In colonies where females consumed more marine items, they also laid eggs with higher maculation compared with colonies where females mainly consumed terrestrial food.