Status
The Common Tern is classed as Least Concern on the IUCN Red List. It has a large population of 1,600,000–4,600,000 mature individuals and a huge breeding range estimated at 29,200,000 km2 (11,300,000 mi2). Breeding numbers have been estimated at 250,000–500,000 pairs, the majority breeding in Asia. Up to 140,000 pairs breed in Europe. Fewer than 80,000 pairs breed in North America, with most breeding on the northeast Atlantic coast and a declining population of less than 10,000 pairs breeding in the Great Lakes region.
In the nineteenth century, the use of tern feathers and wings in the millinery trade was the main cause of large reductions in Common Tern populations in both Europe and North America, especially on the Atlantic coasts and inland. Sometimes entire stuffed birds were used to make hats. Numbers largely recovered early in the twentieth century mainly due to legislation and the work of conservation organizations. Although some Eurasian populations are stable, numbers in North America have fallen by more than 70 percent in the last 40 years, and there is an overall negative trend in the global estimates for this species.
Threats come from habitat loss through building, pollution or vegetation growth, or disturbance of breeding birds by humans, vehicles, boats or dogs. Local natural flooding may lead to nest losses, and some colonies are vulnerable to predation by rats and large gulls. Gulls also compete with terns for nest sites. Some birds are hunted in the Caribbean for commercial sale as food. 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. Overgrown vegetation may be burned to clear the ground, and gulls can be killed or discouraged by deliberate disturbance. Contamination with polychlorinated biphenyls (PCBs) resulted in enhanced levels of feminisation in male embryos, which seemed to disappear prior to fledging, with no effect on colony productivity, but dichlorodiphenyldichloroethylene (DDE), which results from the breakdown of DDT, led to very low levels of successful breeding in some US locations.
The Common Tern is one of the species to which the Agreement on the Conservation of African-Eurasian Migratory Waterbirds (AEWA) and the US-Canada Migratory Bird Treaty Act of 1918 apply. Parties to the AWEA agreement are required to engage in a wide range of conservation strategies described in a detailed action plan. The plan is intended to address key issues such as species and habitat conservation, management of human activities, research, education, and implementation. The North American legislation is similar, although there is a greater emphasis on protection.
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