New York Natural Heritage Program
Common Tern
Sterna hirundo Linnaeus, 1758
Birds

Threats [-]
Common Tern colonies may be threatened by human disturbance, high predation rates from predators associated with human development, flooding and habitat loss due to storms and rising sea-levels due to global climate change. Boating near saltmarsh islands and beach driving and recreation near barrier beach colonies can disturb nesting birds leaving nests and young vulnerable to predation. Elevated levels of environmental toxins such as DDE, DDT, PCBs, mercury, lead, selenium, chromium, and cadmium have been found Common Tern tissues, feathers and eggs in parts of their range (Hays and Risebrough 1972, Custer et al. 1986, Burger and Gochfeld 1988b, Burger et al. 1992, Bishop et al. 1992, Nisbet 2002). Common Terns are particularly susceptible to the effects of DDE and DDT which can cause eggshell fragility and issues with embryo and chick growth and reproductive fitness in adults. Although concentrations of organochlorides like DDT, DDE, and PCBs affected Common Tern populations historically, concentrations were already declining when first reported in the 1960s and 70s (Bishop et al. 1992, Nisbet and Reynolds 1984, Nisbet 2002). Significant levels of DDE, high enough to reduce hatching success, persisted in Common Terns in some Great Lakes sites into the 1980s (Weseloh et al. 1989, Hoffman et al. 1993). Displacement by Herring and Great Black-backed Gulls has been an issue on coastal sites (Kress et al. 1983) and displacement by Herring and Ring-billed Gulls has been an issue on the Great Lakes (Courtney and Blokpoel 1983).

Conservation Strategies and Management Practices [-]
Management for Common Terns requires protection of nesting habitat from development and human disturbance. Posting tern colonies with conspicuous educational signs and symbolic string fencing prior to the birds arrival in the spring has been beneficial to limiting human disturbance. Discouraging gull colonies at some locations may be necessary to reestablish previous nesting locations and can be done through a variety of methods including culling or disturbance by dogs (Kress et al. 1983, Kress 1997, Nisbet 2002). Researchers at some Great Lakes and Lake Champlain islands have had success deterring gulls by constructing a string grid system over nesting areas (Blokpoel et al. 1997, Nisbet 2002). The terns are able to maneuver around the string while the gulls avoid the site. Management of vegetation may be required at some sites where natural overwash and sand scouring is not occurring and predator control may be warranted in some areas.

Research Needs [-]
Continued monitoring of nesting success in addition to the annual population index counts would be beneficial. This would help identify the most successful colonies for conservation and also highlight threats in colonies with low productivity so that management actions may be taken when necessary. The highest priorities for future research are on the wintering grounds. Common Terns have been found wintering along the coasts of Brazil and Argentina (Hays et al. 1997, 1999), however, their distribution along the Pacific coast of South America is poorly known. Basic information on foraging ecology, energetics, and causes of death are poorly known throughout their winter range on either South American coast (Nisbet 2002).