Plants and Animals
Sterna forsteri Forster's tern
Forster's terns are medium-sized terns (14 in./35.5 cm long) with slender bodies, long pointed wings and deeply forked tails. Their typical call is a low nasal "ky-yarr" and a harsh, nasal, buzzy "za-a-ap". Their 31-inch (78.7 cm) average wingspan distinguishes them from the Caspian tern whose wingspan averages 54 inches (137 cm). In the breeding season adults are snow white below and pale gray above with silvery white wing tips and a long deeply forked gray tail. They have an orange bill with a black tip, a black forehead, crown and nape, and orange legs and feet.
Status and Rank
State Status: T - Threatened (legally protected)
Global Rank: G5 - Secure
State Rank: S2 - Imperiled
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Information is summarized from MNFI's database of rare species and community occurrences. Data may not reflect true distribution since much of the state has not been thoroughly surveyed.
Forster's terns nest far from shore within marshes to avoid many predators. They may use muskrat lodges or floating rack as a base to support the nest.
Natural Community Types
For each species, lists of natural communities were derived from review of the nearly 6,500 element occurrences in the MNFI database, in addition to herbarium label data for some taxa. In most cases, at least one specimen record exists for each listed natural community. For certain taxa, especially poorly collected or extirpated species of prairie and savanna habitats, natural community lists were derived from inferences from collection sites and habitat preferences in immediately adjacent states (particularly Indiana and Illinois). Natural communities are not listed for those species documented only from altered or ruderal habitats in Michigan, especially for taxa that occur in a variety of habitats outside of the state.
Natural communities are not listed in order of frequency of occurrence, but are rather derived from the full set of natural communities, organized by Ecological Group. In many cases, the general habitat descriptions should provide greater clarity and direction to the surveyor. In future versions of the Rare Species Explorer, we hope to incorporate natural community fidelity ranks for each taxon.
The nesting and feeding habits of Forster's terns make them vulnerable to changing land and water uses, especially those due to development of industrial, residential and recreational resources. Remaining habitat is often small and fragmented as well as closer to shore, which leaves nests more vulnerable to wash out by early season storms and predation by many types of predators. Periodic cycles of high water in the Great Lakes further threaten breeding success by delaying the growth of cattails needed to adequately shelter the wrack mats from wind and waves. Recreational boating wakes have had a detrimental effect on the floating aquatic vegetation that Forster's terns use for nesting habitat so efforts should be made to ameliorate these effects. Furthermore, disturbance from the noise of close personal watercraft has also caused desertion of nests and the exposure death of newly hatched chicks therefore regulating boat numbers, boat speed and proximity of travel to the vegetation used by Forster's Tern colonies may also be required.
Migration from first week of April to fourth week of April
Nesting from third week of May to fourth week of June
Migration from first week of August to third week of October
Forster's terns may be surveyed like other colonial nesting waterbirds by foot, boat, or aircraft. Care should be taken to minimize disturbance to the nesting colony in order to avoid nesting failure due to abandonment and predation.
Survey Period: From first week of May to fourth week of July
Time of Day: Daytime
- Bibby, C.J., N.D. Burgess, and D.A. Hill. 1992. Bird Census Techniques. Academic Press, New York.
- Hyde, D. 2001. Special Animal Abstract for Sterna forsteri (Forster’s tern). Michigan Natural Features Inventory, Lansing, MI. 4pp.