Glaucous-winged Gull Behaviour

Feeding, Hunting & Foraging Behaviour of the Glaucous-winged Gull

Glaucous-winged Gulls scavenge and prey on other animals for food. Like most gulls, they will scavenge leftovers birds of prey and humans, but mostly eat small fish and marine invertebrates caught at sea or along the seashore. Mussels are torn from rocks and clams are broken open by dropping them on the hard surfaces. They eat refuse where it is available and scavenge spawning salmon carcasses.

Flight Patterns of the Glaucous-winged Gull

Glaucous-winged Gulls fly with powerful and steady wingbeats often in straight and steady flight. Sometimes, they will soar on thermals created by updrafts.

Aggressive, Defensive & Territorial Displays of the Glaucous-winged Gull

Displays used by gulls were wonderfully described in Nobel prize winning zoologist Nikko Tinbergen’s 1953 classic The Herring Gulls World. The displays of the Glaucous-winged Gull are nearly identical to those of the herring gull and they are often but not exclusively used at the nesting colonies.

Threats often begin with an upright threat display that involves a rigid upright stance with the neck outstretched and forward while pointing the head and bill downwards. The wings are lifted slightly so that they stand out ready to strike a blow. In this stance, the gull strides stiffly toward its opponent. In most cases, the opponent backs down but if not, the threat can escalate into a fight. The approach turns into a run and the wings are extended. If the opponent is not ready to fight, it will raise the head and bill slightly and turn away. Often before a fight ensues, the protagonists will begin a tug-of-war with grass tussocks. The final assault begins when one gull rushes the other, delivers a sharp jab with the bill and attempts to grab a wing, tail or leg. A tug-of-war begins until one finally springs free.  Tugging can go on for many minutes. If one gull gets the upper hand, it will strike its opponent several sharp jabs with the wings or peck at its head with the bill. Choking displays are mostly given between a mated pair of gulls. It involves the pair rushing toward another pair of gulls, bending the legs, lowering the body and pointing the bill as if to peck the ground. The head is jerked rapidly while they utter a guttural hoh-hoh-hoh sound.

Courtship & Breeding Behaviour of the Glaucous-winged Gull

The breeding season begins in mid-May in the south and June in the north, and extends into August and September. Glaucous-winged Gulls produce 1 brood per year. Many gulls nest with the same mates each year if they were successful. First-time breeders arrive alone and do not hold a territory at first. They settle in resting areas referred to as clubs by seabird biologists. Clubs are non-territorial areas at colonies where breeding and non-breeding birds assemble to preen feathers, snooze, and rest. Rarely do fights break out.  

It is very likely that individual gulls recognize each other from previous experiences. First-time breeding females choose their mates by approaching a male on a territory. She adopts a posture with her head held horizontal to the body axis and the neck withdrawn. She tosses her head and bill upward uttering a subdued mewing call, all the while walking around him in circles. His response is usually to turn away and punish any nearby male that attempts to approach, feign disinterest, or walk with her a short distance and begin to choking displays.  

Mated pairs work together to defend a territory from other gulls although the males do most of the defending. A nest will be built in the territory that includes an area about 10 m² and where copulation occurs. Gulls copulate following a long display of head tossing, prancing about each other, and mewing calls. Often the males will provide some food to females before copulation, likely to contribute to the formation of her eggs. The male stretches his neck forward and up while the female crouches and mews. He climbs on to her back, bends his legs and utters a hoarse grunting call. The female continues to toss her head against him while he moves his tail until his cloaca touches hers. He then leaps from her back and the pair stands, wag their tails and begin to preen.

Glaucous-winged Gull Nesting Habits

Most Glaucous-winged Gulls breed in colonies of a few pairs to thousands of individuals on coastal rocky islets, roof tops, pilings, and breakwaters. In 1993, seabird biologists estimated the world’s breeding population to be about 200,000 pairs of which about 133,000 pairs bred in Alaska, 29,000 in British Columbia, 10,000 pairs in Washington, 100 pairs in Oregon and 20,000 in Russia. The nest is characterized by a saucer shaped pile of mostly grasses and seaweeds, with the occasional feather, bits of wood and bone, paper in the structure. They are often built on rocky ledges, or partially concealed in grass tussocks, but many nests are also found in open areas. Eggs are a duff brown or greenish blue background hue with chocolate coloured scrawl markings. The average clutch size of hundreds of nests examined in Alaska and British Columbia was between 2.05 and 2.82 eggs.  

Incubation requires about 26-29 days. Eggs hatch into downy chicks with heavy blackish-brown spots. They are fed by both parents a diet of fish and marine invertebrates caught in the marine waters near the colony. As the chicks age, their downy feathers are replaces with flight feathers and they depart the colonies wearing a dull brown plumage. It will take 3 or 4 years to attain the white a pearl grey adult breeding plumage. The number of chicks that reach fledging age (i.e. capable of flight) is slightly more than 1 for each egg laid in most colonies.  The young gulls practice lift and strengthen wing muscles by hopping about the territory and hovering in strong winds. The first flight takes place about 50 to 60 days after hatching.

 Glaucous-winged Gull Vocalizations

Among the many vocalizations given by Glaucous-winged Gulls the calls most often heard signal their threatening, greeting, and mating intentions. The most frequently heard call is a trumpeting keer, keer, keer call given when gulls are anxious or wish to threaten other gulls. The call rings out over nesting colonies day and night, and is uttered where gulls gather. Female gulls utter a subdued mewing call when they are prepared to mate that resembles a cat’s meow. It has been described to sound like klioo klioo klioo. Copulating males utter a deep rapid hoh-hoh-hoh sound. Young gulls give peeping sounds in the egg and when they are very young. Gradually the calls sound like mew-mew-mew.