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Species of Concern

Common Tern Status Assessment


EXECUTIVE SUMMARY Go here for the complete 95 page status assessment (PDF; 695 KB)


During the past several decades, a number of studies have reported significant declines in local populations of the Common Tern (Sterna hirundo) in the Great Lakes region. Concern for Great Lakes Common Terns is further supported by special listing status for this species in 6 of 9 states bordering the Great Lakes. Additionally, the Great Lakes population of the Common Tern is a U.S. Fish and Wildlife Service (USFWS) nongame bird species of management concern. The USFWS contracted the authors of this document to: evaluate the current status of the Great Lakes population in 1995, summarize Common Tern life history, determine major threats to Common Terns in the Great Lakes region and summarize management/protection efforts and priorities for this species. For this report, the boundaries of the Great Lakes population are assumed to be all islands and mainland shoreline of U.S. and Canadian portions of Lake Superior, Lake Michigan, the St. Marys River, Lake Huron, Lake St. Clair, the St. Clair River, the Detroit River, Lake Erie, Niagara River, Lake Ontario and the St. Lawrence River downstream to Cornwall, Ontario. Based on band recovery data and recommendations from state and provincial biologists we also include population estimates and biology from inland colony sites in Minnesota, Wisconsin, New York and Vermont. The only binational censuses conducted to date (1989/90; 1997/98) estimated approximately 10,000 and 7,500 pairs of Common Terns within 1 km of Great Lakes shoreline. Adjusting this estimate to include adjacent inland sites indicates a regional population of about 8,500-11,000 pairs at the beginning of 21st century. When examined on a state or provincial basis, there is very strong evidence that Common Terns have experienced significant population declines between the time first estimates were made (1927-1960) and the present (1997). Using this historical perspective, only one state (Vermont) has recorded a population increase. Three populations in states with historically small numbers (<50 pairs) (Illinois, Indiana, Pennsylvania) are essentially extirpated. The remaining populations in 5 states (Minnesota, Wisconsin, Michigan, Ohio, New York) and 1 province (Ontario) all experienced significant declines during the 1900's.


Common Terns are affected by a diversity of threats in the Great Lakes region. The most serious problems include destruction and modification of habitat and predation. Habitat loss is caused by competition with Ring-billed Gulls (Larus delawarensis) for nest habitat and annual variation in amount of available habitat based on fluctuating Great Lakes water levels. Predation causes mortality of eggs, chicks and adults and results in significantly lowered reproductive success at some colony sites. Other important threats include human disturbance and contaminants.


Threats impacting terns have resulted in extensive knowledge and tested methodology to enhance colony productivity and protection in the Great Lakes. These include habitat management (e.g. habitat restoration, enhancement, creation, and acquisition), predator control, eliminating or minimizing competition for nest sites, and prevention of human disturbance.


Long term survival of the Common Tern in the Great Lakes region requires monitoring, research, intensive local management, communication and conservation. The following are region-wide research and management priorities: (1) a reliable, periodic, coordinated international census , (2) identification of a network of important breeding sites, (3) identification of important colonies in need of special attention, (4) communication with state and provincial governments regarding the importance of consistent and coordinated monitoring and management, (5) standardized methods for collecting and reporting population trend data, (6) collation of extensive information on methodology for enhancing Common Tern survival and reproductive success, (7) analysis of North American band recoveries to ascertain biological population boundaries and facilitate management coordination, (8) recognition of the important role contaminants may play in the long term survival of this species and (9) the need for information on the biology and distribution of Great Lakes Common Terns during migration and winter.


Preparation of this status assessment was initiated in 1995 and a draft report was completed in 1996. Shortly after its preparation, several related research efforts were undertaken by report authors (e.g. 1997 international census, an analysis of North American band recoveries, and prioritization of Common Tern breeding sites for conservation). The original report was delayed to incorporate results of these newer efforts into the final status assessment for this species. It is important to note that with the exception of the newer studies, most of the original information collected for the draft report is based on data collected in 1995.


Go here for the complete 95 page status assessment (PDF; 695 KB)


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