Gulls are the most familiar seabirds of northern temperate regions, regularly seen hunting along the shore for intertidal prey. Or straying far inland in search of food and breeding sites. As a group, they are outstand-in opportunists, which partly distinguishes them from their close but more specialized relatives, the terns, and skuas.
In adapting to a wide variety of lifestyles, gulls range enormously in size, from the dainty and diminutive little gull to the heavily built piratical Great black-backed gull. The larger species have robust, slightly hooked bills, while the smaller species have slender, forceps-like ones. In most species, the underside is white, with gray or darker coloring on the back and upper sides of the wings. The generally pale coloring below is thought to make the flying bird less con-spacious to its fish prey below in the surface waters of the sea. A minority, notably the aptly named Lava gull and the Sooty gull are much darker all over.
The bill and legs of gulls are usually yell-low or bright red, but there is much variation, both between species and at different times of year in the same species. However stoutly built, gulls are always graceful in-flight, switching easily from powerful forward flight to gliding and soaring, their maneuverability serving them well on updraughts near cliff nesting sites. They are equally at home on the water’s surface, where their webbed feet provide ample propulsion.
They are less accomplished divers than that-terns, but some, such as the kittiwake if: Lesser black-backed gull, do make use of aerial plunging to catch fish. Most gulls fall into one of two major us groups, distinguished by the summer plumage, pattern.
Although the gulls enjoy worldwide distribution, the largest concentrations occurring the Northern Hemisphere, where they have succeeded in colonizing the harshest of marine environments. The Ivory gull, for example, breeds in the presence of pack ice and snow where none but the hardiest vegetation survives.
Although gulls are well represented in temperate and subtemperatelatitudes, they are more sparsely distributed in the tropics; this has been attributed to a relative lack of shore food. Although most gulls live on or near the coast throughout much of the year, others live deep in the heart of the continents. The Great black-headed gull and the rare Relict gull thus breed on islands in the inland seas and lakes of the central Asian steppes, many hundreds of kilometers from the nearest ocean.
At the end of the breeding season, when adherence to a colony on land is no longer required, many gulls disperse into offshore waters and some, like the kittiwake, then lead a truly open-sea (pelagic) existence, British-bred birds journeying as far as the coasts of Canada. While there may be a strong random element in such dispersal, birds often congregate at food-rich cold-water upwellings at the edge of continental shelves. Compared with the terns and skuas, however, rather few gull species are true migrants.
A notable exception is Sabine’s gull, which has a circumpolar breeding distribution but at the end of summer migrates south through the Atlantic and Pacific to winter off Africa and South America the bulk of the Atlantic migrants cross the Equator and make for the productive BenguelaCurrent off Namibia and South Africa. Gales in the fall not uncommonly blow Sabine’s gulls towards the British coast, where enthusiastic bird-watchers delight in identifying these rare and elegant visitors. Some species regularly migrate overland. Like Franklin’s gull, which passes in the spring and falls over the Great Plains of North America.
Outside the breeding season, gulls typically continue to be highly gregarious, often assembling in massive flocks for feeding. Roosting and bathing. The favored roosting sites are extensive open areas that offer a good all-around view for early detection of ground predators. Gulls often loaf on the flat expanses of airfields, where they can present a serious obstacle to low-flying aircraft.
All gulls can store substantial quantities of food in their crops, which they regurgitate when feeding mates or young. Birds usually settle at their night roosts with full crops. And leisurely digestion follows. Indigestible parts of the meal are periodically disgorged in the form of pellets. Analysis of -these give a good idea of the diet.
Gulls have a range of feeding habits unparalleled in almost any other group of birds. In the Arctic, for example, where there is a limited variety of prey, Glaucousand Ivory gulls regularly eat the feces of marine mammals and also associate with whales to exploit the invertebrates they force to the surface.
Swallow-tailed gulls are exceptional among gulls in feeding entirely at night. Their large eyes help them to detect and capture fish or squid. Intemperate latitudes. The flexibility and ingenuity of foraging habits are just as striking as Herring mills and their kin smash open41difisit by caring them to a height and dropping them onto the rocks below.
Many Herring gulls have, during this century. Cashed in on the abundance of food offal on garbage dumps, and in consequence, have increased remark-ably in numbers during recent years. Gulls which breed inland also enjoy a wide variety of natural foodstuffs. The smaller species such as little and Franklin’s gulls dip tern-like to pluck insects as small as midges from the water or land.
Many species follow the plow for earthworms and other soil creatures. The Lesser black-backed gull, which is essentially a fish-eating species, income places includes large numbers of Worms in its diet. In the fall, stubble grain provides a valuable bonus on agricultural land.
The larger gulls often prey on birds and mammals that share their breeding stations. The Glaucousand gull is an important predator of Little auks, while the Great black-backed gull plunders a wide variety of seabirds, notably puffins, and can dispatch a good-sized rabbit. Gulls have also learned, skua-like, to harry other seabirds, forcing them to disgorge their food; terns that share colony space with, for example, Black-headed or Silver gulls, regularly suffer from such piracy.
Sometimes gulls shadow foraging ducks, cormorants, or pelicans, and rob them as soon as they surface with prey. In the same way, Black-headed and Common gulls are frequently found in fields among flocks of lapwings, which are greatly superior in the art of locating and extracting earthworms; the gulls are quick to pounce on a successful lapwing to relieve it of its worm. In Australia. The Silver gull has begun to forage on plowed fields far inland, repeating a pattern found in other parts of the world where man has developed arable farming on a significant scale.
In most regions, gulls breed once a year during a well-defined season those cur-responds with the summer flush of food in the environment. In the tropics, where the food supply is less seasonal, more complex patterns may occur. The Swallow-tailed gull, for example, is known to breed every month of the year; pairs that raise young successfully will mount another breeding attempt 9—to months later, unsuccessful birds sooner still. In southwest Australia, the Silver gull may breed twice a year, inspiring and falling, a unique pattern.
Gulls are generally monogamous and usually pair for as long as both members survive. However, in species such as the kit-tweak, divorce is not uncommon, especially among inexperienced birds, and individuals will seek a new mate if the existing pair bond proves unfruitful. As the breeding season approaches, gulls typically assemble in large, dense colonies, frequently reclaim-in their nest site of the previous year. Many species breed on cliff ledges or atop coastal islands, while inland species often seek the safety of a marsh. Common gulls may build their nests on the stump or fork of a tree up to zoom (33ft) above the ground, also not uncommonly on stone walls and buildings. In keeping with their growing use of man’s domain, Herring gulls are also favoring roof-tops, chimney stacks, etc.
The kittiwake, a gull of the open seas for much of the year, also sometimes adopts a window ledge as a substitute for its usual cliff-nesting habitat. The Gray gull breeds in one of the most inhospitable habitats chosen by any bird—the hot, arid deserts of Peru and Chile, while Ivory gulls sometimes nest on stony patches on ice floes.
The density of nesting depends partly on the local food supply. In temperate regions, where fish stocks are high in summer, many gull species breed in huge colonies, siting their nests only a meter or so from one another, and defending a territory little larger than the nest itself. Such gulls are notably successful in ousting smaller com-Petites from their nesting space, and populations on the increase often com-politely expel less competitive seabirds from
Islands. On the Isle of May, in Scotland, where Herring gulls increased from a soli-tarry pair in 1907 to over 14.000 pairs in the space of 6o years, terns were forced to abandon the island as a breeding site. Where the food supply is less plentiful, gulls may nest much more sparsely. In an extreme case, Lava gulls, which number about 300-400 pairs and occur only on the Galapagos Islands. Typically nest over 3km(1.9 mi) from each other.
In species that nest densely, there is much rivalry as the pairs stake out territories at the start of the breeding season; males are the main aggressors, but the females also join in. Gulls command an unimpressive repertoire of aggressive and appeasement displays and calls during these contests. Although prolonged fights sometimes take place, most of this behavior is ritualized and injuries are avoided.
Black-headed gulls, for example, regularly avert their heads (”head-flagging”) when squaring up to one another, so hiding the pro-vocative black mask and bill. Rival Herring gull males may symbolically tug and tear at the vegetation along a contested territorial boundary, then each may claim victory by throwing their heads back and “long-calling” vociferously, before resuming hostilities. Such shows of strength also attract females, which typically approach bachelor males tentatively in a submissive cowed posture. Once accepted by the male, the female is fed by the male as a prelude to egg-laying.
The clutch is typically 2-3; the tropical Swallow-tailed gull is unique in laying only one egg. Both sexes share incubation, changing over several times each day until the eggs hatch, usually after about four weeks. The emerging young are mobile as soon as their down dries but remain in or near the nest for a week or so where their parents can brood and tend them closely. When small, they jostle for food by pecking at the parent’s bill: in some species brightly colored spot near the parent’s bill tip serves as a target and stimulus for this begging action. Once liberated from the need for brooding, the young may seek refuge in vegetation, etc near the nest. If they trespass onto neighboring territories they are often fiercely attacked by the owners. Injury and even death may result.
In the larger gulls, some adults specialize in killing the young of other broods and feed-in them to their offspring. At one Herring gull colony, it was observed that almost a quarter of all h things was cannibalized in this way and many eggs were also pirated. In species that lay three eggs, the last laid egg is typically the smallest. Gull clutches hatch over a few days so that the last chick has to compete with larger siblings. This third “runt” chick is therefore prone to succumb if food is short and more likely to fall victim to adult cannibals.
Occasionally, a cannibal Herring gull has difficulty distinguishing the instinct to nurture its offspring from the urge to kill and eat the young of other pairs. One such adult ate over 4o chicks while sharing the incubation of its clutch. When its brood hatched, it continued to bring live chicks to its nest site but failed to kill them. Over a week, it added eight live healthy young to its brood. The task of raising this extended family proved insurmountable in the end, but one of the adopted young was successfully raised to fledging.
By the time the young leave the nest at 3-7 weeks (depending on species), they are irefully feathered. But in a mottled brown garb quite different from their parents. This dress was lost by degrees. Until the breeding age is reached. The parents usually continue to feed their offspring for some time after fledging, up until z months afterward in some of the larger gulls.
Like other seabirds, gulls that survive the rigors of juvenile life can, on average, look forward to a relatively long life. Ringing studies show that Black-headed gulls and Herring gulls can live over 3o years. Presumably, because breeding is hazardous to venture, requiring considerable experience, and gulls generally do not breed until they are several years old—two years in little and Black-headed gulls, usually five in Herring and Lesser black-backed gulls.
When they approach breeding age. Some birds may return to the colony where they were born to establish a territory, and they sometimes settle remarkably close to their natal nest site. However, other gulls may travel considerable distances to join other colonies, a dispersal that probably helps to mitigate the possible adverse effects of inbreeding.
Many, but not all, gull species have probably never been as numerous as they ardor, given the new food supplies made available by man. Foremost among scarce gulls is the Relict gull, of which no more than 1,500-1,800 pairs are known from Lake Alake and Lake Barun-Torey deep in the interior of the USSR.
Terns are among the most graceful and appealing inhabitants of shorelines and marshes. Many are familiar summer visitors to north temperate coasts, catching the eye with their winnowing flight and spectacular plunge-diving for fish. Some, like the mass-vie Caspian tern, show the close kinship of terns with the gulls, while the resemblance of other members to the skimmers is also evident.
Most terns (22 species) belong to the “black-capped” group of species of Sterna. These sea terns or “sea swallows” have as lender form, long tapering wings, a deeply forked tail, and are agile in flight. The typical plumage pattern is white below and gray above, with a black crown which in some species is crested. Juveniles are often mottled brown, especially on the back, and May take 2-3 years to assume an adult appearance.
In the marsh terns (three species of Caledonians)and nod dies (three species of Arouse), the plumage is generally darker or even black. Conspicuously different is the slate-blue Inca tern, with its yellow gape wattles and white mustache. Among- the terns, the bill— often bright yellow, red, or black–varies in shape from pincer- to dagger-like, depending partly on the size of the prey taken. The flight, though buoyant, is strong, often allowing a sustained hover. Although the feet are webbed, most terns seldom settle on the water for long.
The terms are to be found worldwide, extending to all but the highest, ice-fast latitudes. Habitat preference divides the species broadly into two groups. Sea terns and marsh terns. Some sea terns. Such as the Roseate tern and Caspian tern, are among the most cosmopolitan of all birds. While the majority prefers warm tropical and subtropics-cal Waters, others favor colder latitudes for breeding, and the sea terns thus range from the Arctic to the Antarctic. By contrast, the marsh terns have adopted a largely inland Existence, on freshwater marshes, and lakes drivers, often deep in the heart of continents.
Terns undertake prodigious migrations, many journeying in summer to the food-rich waters of higher latitudes to breed, and resorting to tropical climes for the winter. The Arctic tern undertakes possibly the longest migration of any bird species. Many breed north of the Arctic Circle and move south to the Antarctic for the northern winter, an each-way journey of someI5,0ookm (9,30omi) “as the crow flies.” By doing so, they exploit the long daylight for prolonged feeding time in both hemispheres.
The ringing of terns and plotting their move-mints has done much to unravel the routes taken; many Canadian Arctic terns, for instance, cross the Atlantic on westerly’s tithe European coast on their way south. While most travel by sea, feeding as they go, overland routes are not uncommon, and many marsh terns, for example, cross the Sahara en route from their breeding grounds to their African winter quarters.
The sea terns are primarily fish-eaters, though squid and crustaceans are also relished. The black-capped terns are bold plungers, spotting their prey as they hover into the wind, before diving headlong (see box). In general, the bigger the tern, the higher and deeper it dives the Caspian tern may plunge from 15m (5oft). Unlike gin nets, terns do not swim underwater, and prey is seized near the surface. Noddiestypically dip to the surface and may use their feet for pattering like storm petrels. They often catch flying fish in mid-air. Nod-dies and some other tropical terns range far offshore to feed, swallowing their prey for later regurgitation to the young.
Though most terns are daytime feeders, some, such as Sooty terns, have been recorded feeding at night. The dainty marsh terns are well adapted for hawking insects or hovering to pluck them off vegetation. They also make shallow plunges for frogs and other aquatic animals. The Gull-billed tern is the most terrestrial of all and swoops to seize large insects, lizards, and even small rodents from the ground. The rate of feeding visits to the young varies according to the distance the parents must travel to hunt. While a marsh tern may feed its young every few minutes, the Sooty tern, which ranges hundreds of kilometers to forage, may only deliver meals once a day.
In common with many other seabirds, most terns are long-lived, if they survive to adulthood. Arctic terns have been shown bringing to live 33 years or more, and a lifespan of 20 years is probably not unusual. Breeding may begin as early as two years, but more often at three or four in temperate breeding species, generally later in tropical species. Most Sooty terns, for example, donor reaches sexual maturity until at least six years old.
In higher latitudes, terns usually have a well-defined breeding season once a year, in Europe from about May to July. In the tropics, breeding is generally not synchronized to a particular time of year. In new populations, however, terns breed both at intervals of less than a year and synchronously. On Cousin Island in the Indian Ocean, Bridled terns breed every 7-1 months, while the highly adaptable Sooty tern breeds, depending on location, at intervals varying from six to 12 months; in some cases, it seems likely that food is more or less equally abundant at all times of the year.
Terns generally pair for life. Even though the pair bond breaks down outside the breeding season, there is a strong tendency to return to a previously successful breeding site, which enables former mates to rendezvous at the start of each new breeding season. Courtship is an elaborate ritual, especially in birds seeking a mate for the first time. In many terms, the first stage of pairings is the “high flight,” in which the male ascends at speed as if to demonstrate his prowess, too often several hundred meters, while the female pursues him.
At the end of the climb the prospective pair glides and zigzags earthwards. With growing familiarity, the male increasingly courtship-feeds his mate; this has more than just sym-boric value—it helps the female to form eggs And perhaps allows her to gauge the fishing skill of her partner. Ground courtship often occurs near the male’s chosen nest site, and involves much elegant strutting and pirouetting with raised tail and drooped wings. This is usually the prelude to copulation.
Most terns breed in bustling colonies, often at high density. They also roost encase and may join together to mob predators at the colony. The colony site is usually on flat open ground, often on an island or reef. Nod dies, however, they crowd on trees, bushes, and cliff ledges, while Inca terns seek crevices in rock. The White tern is celebrated for building no nest, opting to lay its single egg directly onto, usually, the branch of a tree.
Most ground nesters are scarcely more constructive, merely fashion-in a shallow scrape, at the best thinly lined. Noddies and marsh terns, however, build a more substantial platform of vegetation, the latter anchoring a raft of reeds, etc to submerged plants. Both sexes defend the nest territory, often only a square meter or so in extent, while the “crested” terns, which nest most densely of all, may be within a jab-bang distance of neighbors.
The normal clutch varies from one egg in tropical species to 2-3 in higher latitudes; incubation, shared by the sexes, lasts 3-4 weeks. On hatching, the downy chick’s arson actively explores their surroundings but seldom stray far unless disturbed. Then they take refuge in vegetation, or undertones, driftwood, and the like, while the well-grown young of “crested” terns may seek safety in numbers, forming a mobile crèche. Parents returning with food recognize their own young in the crèche by voice and feed only them. After the young fledge, they have much to learn about catch-in prey for themselves and are fed by their parents for some time, before grade-ally being weaned off.
The isolation sought by terns for breeding purposes is an increasingly scarce resource man turns more to the coast and sea for leisure, commercial fishing, and other activities. Pressure on land use in South Africa has reduced the Samara tern to a pre-carious 1,500 pairs while snaring for food and sport in its West African winter quarters is believed to have contributed to the decline of the European Roseate tern to around1, 000 pairs. By contrast, many populations continue to flourish in remote regions, anon Pacific Christmas Island alone, the Sooty tern is numbered in millions.
During their breeding season, skuas and jaegers are the pirates and predators of the skies in high latitudes. They have been seen closer to the South Pole than any other vertebrate apart from man. One individual ringed as a chick at Anvers Island, Antarctica, was shot five months later in God-that fjord, Greenland—the longest journey of any bird ever recorded by ringing. Skuas will harry other seabirds until they disgorge their last meal, which they then catch immix air. In North America and elsewhere the small skuas are called “jaegers,” after the German word meaning hunter. The Great skua has been seen to kill prey many times heavier than itself, such as the Gray heron, Graylag goose, she ducks, and Mountain hare.
Outside the breeding season, skuas migrate over all the world’s oceans, the jaegers also traveling in some numbers directly overland. Records of Arctic skuas in Austria and Switzerland in the fall are not uncommon. The large species, on the other hand. Tend to remain some distance offshore, beta few storm-tossed young Great skuas have been picked up, exhausted, in central Europe. One, ringed as a chick in Shetland. Was rescued from the central reservation of
A motorway in West Germany only to besot a week later as it attacked chickens on an east Austrian farm.
Skuas are closely related to and presumably evolved from, the gulls, which originated in the Northern Hemisphere. However, early in the evolution of the skuas, one form must have colonized the Antarctic, where it has given rise to the three very similar large skua species. The small populations of the Great skua in the North Atlantic are almost certainly recently derived from birds blown north from the South Atlantic, as measurement and plumage of the two subspecies are very similar. The Great skua is thus unique among seabirds in that inbreeds in both the sub-Antarctic and the Northern Hemisphere.
The three species of large skua are generally brown. The Chilean skua has con-spacious refocus underling feathers, while the South polar skua has both dark and light phases (dimorphic plumage) light-phase birds increase in frequency towards the Pole. It is not known why skuas should benefit from having plumage that is paler on the upper parts in regions with more snow and ice.
All three jaegers display two color phases. The dark phase is extremely rare in the Long-tailed Jaeger. In the Arctic and marine jaegers, the proportions of birds of each phase within the population vary geographically. In Shetland less than 25 percent of Arctic jaegers are light; the proportion tends to increase northwards, with nearly zoo percent light in Spitsbergen and arctic Canada. The elongation of the two central tail feathers is characteristic of adult skuas. Is prominent in the Arctic Jaeger and extreme in the Long-tailed Jaeger. ThePomarine Jaeger has twisted club-shaped central tail feathers.
The skuas have feet that are gull-like, but with prominent sharp claws. The bill is hard and strongly hooked at the tip, adapted for forbearing flesh. In gulls, as in many other bird families, males are slightly larger than females, but the opposite is true for skuas, as for birds of prey. In both these groups the male does most of the hunting and the female remains in the territory to guard the thinnest or young.
Skuas take many types of food. Pomarinejaegers feed largely on lemmings in summer and on small seabirds in winter, less regularly by fishing or by harassing other birds (piracy). Long-tailed jaegers feed on lemmings, insects, berries, small birds, and eggs in summer and by piracy, chiefly by harrying terns, in winter. In arctic tundra areas, Arctic jaegers feed on insects, berries, small birds and eggs, and some rodents; in coastal areas, they feed almost exclusively by piracy of terns, kittiwakes, and auks.
Skuas are normally monogamous and pair for life. In New Zealand and on Marion Island, Great skua trios comprising one female and two males occur regularly, a social system not yet found in any other skua. Distances between skua nests vary enormously, from often 2km (1.2mi) apart on the arctic tundra, down to just 5—Iom (16— 33ft) within the largest Great skua colonies
In Shetland. On Foul, Shetland, 306 pairs of Arctic jaegers breed in a colony occupying.7sq km (0. 7sq mi), approximately the area defended by a single pair breeding on the arctic tundra. Part of the explanation for this difference is that skuas nesting in Shetland do not obtain food within their territory, but feed at sea. Skuas defend their nests by dive-bombing intruders, including humans. Jaegers have a “broken wing” dies-traction display.
Skuas have only two brood patches, and birds with three eggs usually fail to hatch any. Most pairs with two eggs manage thatch both, but if food is short, the older chick, which hatches 1-3 days before the second, will attack and kill its smaller sibling. In Shetland, Arctic jaegers begin breeding when 3-6 years old, while Greatskuas first breed when between five and 10 years old. Presumably, this long period of immaturity helps the skua to learn the many skills needed to be an effective hunter and parasite of other seabirds.
Skimmers are among our better-named birds, for they skim the surface of lakes, rivers, and lagoons, deftly snapping up fish with their uniquely adapted bills. They crowd by the hundreds into nesting colonies on sand bars, where the contrast between their brilliant bills and legs, and their stark plumage, make them a prized “target” of wildlife photographers and artists.
Even though the skimmer family is represented by only three species in the world, it is widely distributed. Three subspecies (or races) of the Black skimmer are found in the New World: the North American subspecies inhabits the ocean coasts and the Salton Sean the western USA. The two South Amery-can subspecies are almost exclusively riverine, using coastal areas out of the breeding season. African skimmers are most abundant in East and Central Africa on the larger river systems. Indian skimmers range from Pakistan across India to the Malay
Peninsula, mostly in close association with large rivers.
The Indian and Black skimmers have orange-red bills (but the Black skimmers is black toward the tip) and vermilion legs and feet in the breeding season (duller at other times), while the African skimmer has yell-low legs and feet and a yellow-orange bill. The young of all species are lighter brown above and less white below, and the tail is mottled, unlike the mostly white tail of the adults. The wings are very long, with a span 21 times the length of the bird.
But the most striking feature in all species is the large, scissor-like bill with its flattened “blades,” the upper mandible fitting into a notch between the edges of the lower mandible, which is 1-1 as long again as the upper. It was once thought that the lower mandible had great touch sensitivity, but recently this is not thecae. When feeding, skimmers hold the bill open in such a position that the tip of the lower mandible slices the water. When the lower mandible touches a prey item, usually small fish, the head flexes downward rapidly, trapping the prey sideways between the “scissors” (hence the popular name” scissorbill”).
The musculature of the headland neck is well developed and acts as a shock absorber. Skimmers often feed at dusk and throughout the night, especially in the non-breeding season. The skimmer eye has a vertical pupil, much like that of a cat, which may enhance its light-gathering properties. Skimmers prefer to feed in waters with little surface turbulence, such as lakes, pools, marsh, and river edges. After “cutting trail” in the water, birds often double backend retrace their course, snapping up prey
In their wake. They usually feed alone or impairs, but on occasion groups of 10-15 birds may engage in brief bouts of intense feeding in a particular spot. In coastal areas, feeding increases at low or ebbing tides.
Male Black skimmers are much larger than females. Measurements of wing span, bill, tail, and weight show males ranging from about 1 o percent (wing, tail) to 25 percent (weight, bill length) larger than females. Such dimorphism is not confirmed for African and Indian skimmers.
Skimmers used to be considered more closely related to terns than gulls unlike gulls; neither skimmers nor terns use their wings during aggressive encounters. However, further analysis of breeding behavior suggests that the skimmers split from the ancestral stock before the divergence between terns and gulls. Of the three families, only skimmers have a short-7.1-like “broken wing” distraction display. Skimmers are highly social birds in seasons of the year. When they reach breed-in age (probably at 3-4 years).
They gather on open, sandy bars and small islands w4cgccourtship begins. Vertical flights and aerial chases by courting birds are common at the time. The breeding colonies, established on these sites after a few weeks, range in size from a few pairs up to 1,000 or taut, Slammers often form mixed colonies with terns and they probably benefit from some terns’ “greater display of aggression in driving off predators.
Skimmers have small nesting territories. With nests spaced 1-4m (3.3-13ft) apart depending on vegetation and terrain. The degree to which birds nest at the same time (synchrony) can be very high in certain areas of the colony. Aggression is high during the period of territory establishment and egg-laying, and both sexes engage in disputes over space and mates. The males are more aggressive toward other skimmers. While females more frequently interact with other species nesting nearby. Males incubate and brood more than females.
At least during the day. Males and females switch incubation duties frequently, especially in the hottest part of the day. Foot and belly-wetting by adults help to regulate the temperature of the incubated egg. After the young hatch, the females feed the young more than the males do. Parents feed the young beyond the four-week nestling period, and the fledged young accompany adults on feeding forays, perhaps learning where and how to fish.
The nesting period at a skimmer colony is often considerably longer than that of most of their gull and tern relatives—along the eastern IJSA the Black skimmer may nest from May to October. After the nesting season, skimmers gather in loose flocks to ascertain “staging areas.” They follow major river systems and coastal routes when migrating to distant wintering areas. Some populations of skimmers are non-migratory.
Skimmers are not presently considered threatened. However, damming of rivers in India, Africa, and South America continues to reduce the nesting habitat. This. Coupled with the destruction of tropical forests. Diminishes water quality and productivity which, in turn, affects skimmers’ diets. In North America, many coastal habitats have been disturbed, forcing Black skimmers land other species) to nest on small salt marshlands and even on roofs of buildings in some areas. See more: Sand Plovers