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Common Tern (Sterna hirundo)
Common Tern (Sterna hirundo), a bird listed as Endangered in Wisconsin, prefers the Great Lakes' shorelines, bays, sand bars of large lakes and rivers, sandy or rocky coastal islands, and marshes. The recommended avoidance period is from mid-May through late August.
Status and Natural Heritage Inventory documented occurrences in Wisconsin
The table below provides information about the protected status - both state and federal - and the rank (S and G Ranks) for Common Tern (Sterna hirundo). See the Working List Key for more information about abbreviations. Counties shaded blue have documented occurrences for this species in the Wisconsin Natural Heritage Inventory database. The map is provided as a general reference of where this species has been found to date and is not meant as a range map.
|Federal Status in Wisconsin||none|
|Tracked by NHI||Y|
Common Tern (Sterna hirundo) has very few known occurrences in the state and is of the highest priority for conservation; we encourage you to consult with your District Ecologist or an NHI Zoologist for specific recommendations for your site.
Note: a species guidance document is not available at this time. Information below was compiled from publication ER-091.
Identification: Distinguished from Forster's tern by red bill and legs, darker upper wing surface and wing tips, and black outer edge on tail feathers.
Habitat: Common terns nest on isolated, sparsely vegetated islands or peninsulas in large lakes. Sandy substrates are typical.
State Distribution: Common migrant and uncommon resident north and east. Five nesting colony sites occur in Wisconsin: lower Green Bay, Lake Butte des Morts, Lake Winnebago, and Chequamegon Bay and Duluth-Superior Harbor. A map outlining Pre-1977 and 1997 to Present Distribution is available.
Diet: Primarily small fish.
Clutch: Usually nest at age 3.usually 3 olive or brown eggs; laid from late May to early June.
Incubation: 21-28 days by both parents. Fledging occurs around 28 days after hatching.
Nest: Slight depression in soil lined with grasses, seashells, or bits of seaweeds. Nest in colonies.
Management Guidelines: Habitat loss, prolonged inclement weather, nest predation, human disturbance, displacement by gull species, and possibly chemical contaminants are factors affecting nesting terns. Human disturbance near colonies during the nesting season should be prevented. Preferred nesting sites contain 10-30% vegetative cover. Sites should be managed accordingly to provide sparsely vegetated areas that are free of avian and mammalian predators, such as great horned owls, minks, rats, raccoons, and red foxes.
Links to additional Common Tern information
- All About Birds Species Account (Cornell Lab of Ornithology)
- Wisconsin All-Bird Conservation Plan
- Michigan Natural Features Inventory
- NatureServe Explorer information
Other links related to birds
Wildlife Action Plan
Information from Wisconsin's Wildlife Action Plan.
Native community (habitat) associations
The table below lists the natural communities that are associated with Common Tern. Only natural communities for which Common Tern is "significantly" (score=3) or "moderately" (score=2) associated are shown. Please see the Wildlife Action Plan to learn how this information was developed.
Ecological landscape associations
The table below lists the ecological landscape association scores for Common Tern. The scores correspond to the map (3=High, 2=Moderate, 1=Low, 0=None). For more information, please see the Wildlife Action Plan.
Landscape-Community combinations of highest ecological priority*
Ecological priorities are the combinations of natural communities and ecological landscapes that provide Wisconsin's best opportunities to conserve important habitats for a given Species of Greatest Conservation Need. The 10 highest scoring combinations are considered ecological priorities and are listed below. More than 10 combinations are listed if multiple combinations tied for 10th place. For more information, please see the Wildlife Action Plan.
* Ecological priority score is a relative measure that is not meant for comparison between species. This score does not consider socio-economical factors that may dictate protection and/or management priorities differently than those determined solely by ecological analysis. Further, a low ecological priority score does not imply that management or preservation should not occur on a site if there are important reasons for doing so locally.
- Long-term conservation and management of dredge spoil sites and other island sites that can be all or partially managed for nesting Common and Caspian Terns is recommended.
- Managing inland and coastal, sparsely vegetated, island sites for Common and Caspian Terns as part of an ecosystem approach to species restoration and recovery is recommended. The use of tern decoys and sound systems may help attract both species to pote
- Partnerships between state and federal agencies and private organizations dedicated to the conservation of coastal ecosytems will benefit the long-term management of both Common and Caspian Terns.
- Public education programs and presentations of long-term tern monitoring efforts will reinforce the importance of both species to coastal environments, particularly along the Great Lakes.
- Regulations that limit/monitor/prevent the presence of organochlorine contaminants as part of an overall strategy to monitor contaminat loads in coastal ecosystems are recommended.
- Research, training, and communication that identifies both Common and Caspian Terns as integral components of coastal ecosystems will aid conservation and management.
- The long-term use, and planning for, dredge spoil sites should include a component for tern management.
Threats and issues
- Common Terns require sparsely vegetated substrates, typically on islands associated with large inland lakes and the Great Lakes. Vegetative succession reduces or eliminates breeding habitat availability.
- Habitat loss and competition for nest sites with Ring-billed Gulls and Herring Gulls
- Mammalian predation of eggs or young - especially mink (and to a lesser extent avian predation, especially migrant Ruddy Turnstones that predate eggs)
- Prolonged inclement weather and associated high wave action
- Coastal development may impact tern colony sites by reducing or eliminating potential breeding habitat. Associated with development may be a greater threat of human disturbance.
- Since the early 1970s, organochlorine and other chemical contaminants, such as PCBs and DDE (DDE concentrations exceeding 4 ppm in eggs) have affected Common Tern eggshell thickness and structure, caused various eye, bill, and feet deformities, and contributed to aberrant beahviors of breeding adults.
- Common Terns formerly nested on sandy peninsulas or islands accessible by recreating humans. These sites have been all but abandoned by breeding terns. Nesting Common and Caspian Terns are now largely restricted to dredge-spoil islands, a managed former pier remnant, or remote gravel islands.