All the flight feathers of the Arctic tern are translucent against a bright sky, only the four innermost wing feathers of the common tern share this property. The most distinctive sound is the alarm KEE-yah, stressed on the first syllable, in contrast to the second-syllable stress of the Arctic tern. Sexes are similar. [86] When adults take food back to the nest, they recognise their young by call, rather than visual identification. The common tern breeds in colonies which don’t usually exceed 2,000 pairs,[44] however might often quantity greater than 20,000 pairs. Eggs and young are vulnerable to predation by mammals such as rats and American mink, and large birds including gulls, owls and herons. This capability to find the eggs is an adaptation to life in an unstable, wind-blown and tidal setting. Breeding success could also be enhanced by way of floating nest rafts, man-made islands or different synthetic nest websites, and by stopping human disturbance. Eggs and younger are weak to predation by mammals resembling rats and American mink, and huge birds together with gulls, owls and herons. Flat grassland or heath , or even large flat rocks may be suitable in a island environment. It weighs 110–141 g (3.9–5.Zero oz). The eggs are cream, buff, or pale brown, marked with streaks, spots or blotches of black, brown or grey which help to camouflage them. The common tern tends to make use of extra nest materials than roseate or Arctic terns, though roseate typically nests in areas with extra rising vegetation. [ 53 ] Forster’s tern has a more extensive black tip on the bill and longer legs, best seen when it is sitting. The common tern tends to make use of extra nest materials than roseate or Arctic terns, though roseate typically nests in areas with extra rising vegetation.Terns are professional at finding their nests in a big colony. Varela, F J; Palacios, A G; Goldsmith T M (1993) "Vision, Brain, and Behavior in Birds" in Zeigler & Bischof (1993) pp. This phenomenon is named a “dread”.This autumn juvenile in Massachusetts has a white brow, having misplaced the ginger colouration attribute of youthful birdsOn their return to the breeding websites, the terns might loiter for a couple of days earlier than settling right into a territory, and the precise begin of nesting could also be linked to excessive availability of fish. This distinguishes common terns from other medium-sized, commonly-confused, terns such as Forster's tern and the arctic tern. Overgrown vegetation could also be burned to clear the bottom, and gulls might be killed or discouraged by deliberate disturbance. Other vocalizations include a kakakakaka when attacking intruders, and a staccato kek-kek-kek from fighting males. Contamination with polychlorinated biphenyls (PCBs) resulted in enhanced ranges of feminisation in male embryos, which appeared to vanish previous to fledging, with no impact on colony productiveness, however, dichlorodiphenyldichloroethylene (DDE), which ends from the breakdown of DDT, led to very low ranges of profitable breeding in some US places. [20] There are small and erratic colonies in West Africa, in Nigeria and Guinea-Bissau, unusual in that they are within what is mainly a wintering area. [89] Breeding success may be enhanced by the use of floating nest rafts, man-made islands or other artificial nest sites, and by preventing human disturbance. There is a record of a common tern taking over a spotted sandpiper nest and laying its eggs with those of the wader. Its pointed wingtips are noticeably darker than those of the roseate tern with which it associates. The rare common tern bird nests on this island – one of only two tern colonies remaining on Lake Superior – but has become threatened by habitat loss in recent years. [41], New World birds winter along both coasts of Central and South America, to Argentina on the east coast and to northern Chile on the west coast. Particularly within the early a part of the breeding season, for no identified purpose, most of the entire terns will fly in silence low and quick out to sea. Most populations of the common tern are strongly migratory, wintering south of their temperate and subarctic Northern Hemisphere breeding ranges. Rafts are rarely used by other tern species. The chicks fledge in 22–28 days, normally 25–26. [65] Despite the aggression shown to adults, wandering chicks are usually tolerated, whereas in a gull colony they would be attacked and killed. The primary breeding try is normally at 4 years of age, generally at three years. Second clutches are possible if the first is lost. Despite international legislation protecting the common tern, in some areas populations are threatened by habitat loss, pollution or the disturbance of breeding colonies. Common Terns are occasionally seen in freshwater swamps, floodwaters, sewage farms and brackish and saline lakes. The common tern is classed as least concern on the IUCN Crimson Listing. There are a variety of comparable common tern species, together with the partly sympatric Arctic tern, which might be separated on plumage particulars, leg and bill colour, or vocalisations. [70] Breeding success in areas prone to flooding has been enhanced by the provision of artificial mats made from eelgrass, which encourage the terns to nest in higher, less vulnerable areas, since many prefer the mats to bare sand. [58] It may circle or hover before diving, and then plunges directly into the water, whereas the Arctic tern favours a "stepped-hover" technique,[87] and the roseate tern dives at speed from a greater height, and submerges for longer. Tapeworms of the family Cyclophyllidea may also infect this species. It has a direct flight, hovering above water before diving for prey. [36] A down-slurred keeur is given when an adult is approaching the nest while carrying a fish, and is possibly used for individual recognition (chicks emerge from hiding when they hear their parents giving this call).