Forster's Tern (Sterna forsteri) Dick Daniels

Forster's Tern (Sterna forsteri)
Dick Daniels

Class
Aves (Birds)
Family
Laridae (Terns, Gulls and Relatives)
State Protection
Protected Bird
Defined as a Protected Bird by New York State law, and the species may not be hunted or taken at any time in New York. Includes birds also defined as a game species, but for which no open seasons are set.
Federal Protection
Not Listed
State Conservation Status Rank
S1
Critically Imperiled in New York - Especially vulnerable to disappearing from New York due to extreme rarity or other factors; typically 5 or fewer populations or locations in New York, very few individuals, very restricted range, very few remaining acres (or miles of stream), and/or very steep declines.
Global Conservation Status Rank
G5
Secure globally - Common in the world; widespread and abundant (but may be rare in some parts of its range).

Summary

Did you know?

Forster's Terns are the only terns whose summer (breeding) and winter (non-breeding) ranges and migration range are located almost completely in North America.

State Ranking Justification

Forster's Terns are a recent addition to New York's avifauna with the first nest found in the state in 1981 (Levine 1998). New York is the northern extent of their eastern range. They are currently threatened by habitat loss and historically, in parts of their range, populations have likely been affected environmental toxins (1960s-1970s) and hunting for feather collection by the millinery trade, or hat making industry (1880s). As populations increase in New York they may be restricted by habitat availability, human disturbance and rising sea-levels due to climate change.

Short-term Trends

The distribution and numbers of Forster's Terns have increased in New York over the past few decades. They were found in only 2 atlas blocks during the first Breeding Birds Atlas in 1980 to 1985, and in 10 blocks in the second Breeding Bird Atlas in 2000 to 2005 (Andrle and Carroll 1988, McGowan and Corwin 2008). They are known as a breeder in the state only since 1981 (Zarudsky 1981) and have been increasing in numbers, slowly, since this time (McGowan and Corwin 2008). They are currently known from roughly 12 colony locations in the state although colony presence at any particular site in a given year as well as colony numbers fluctuate broadly between years (NYSDEC 2011).

Long-term Trends

The first breeding record of Forster's Terns in the state was in 1981 (Levine 1998). Because the species is a relatively new addition to New York's avifauna, the long-term trend is increasing.

Conservation and Management

Threats

Forster's Terns have been affected by habitat loss, hunting for feathers by the millinery trade, or hat making industry (1880s), and likely by environmental toxins (1960s-1970s) in parts of their range. Current threats in New York include human disturbance, flooding and habitat loss (Mcnicholl et al. 2001). Recreational boaters driving at high speeds or anchoring near salt marsh islands may disrupt terns from parental care of eggs and chicks leaving them vulnerable to predation. Mortality due to hypothermia has been reported when young chicks fled to the water in response to observers near nesting locations (Hall 1989, Fraser 1994a). Although Forster's Terns don't occur in large numbers in New York, populations may be threatened by habitat loss. A combination of factors may contribute to the dramatic declines of coastal salt marsh observed on Long Island over the last 50 years (Hartig 2002). Sea-level rise and increased storms and flooding due to global climate change is a threat to the salt marsh habitat that Forster's Terns require for nesting. Changes to hydrologic processes resulting from coastal development coupled with increases in sedimentary sulfide associated with human development are also believed to play primary roles in the decline of coastal salt marsh (Montalto and Steenhuis 2004, Kolker 2005).

Conservation Strategies and Management Practices

Management for Forster's Terns requires both the protection of existing colonies to enable populations to perpetuate and grow, and the restoration and protection of habitat for terns to move into as populations expand or disturbed colonies need to relocate. Managing predators may be effective in certain circumstances where nest predation is high as has been effective for other tern species (Molina et al. 2010). Maintaining and protecting habitat at a number of suitable nesting locations is ideal even if some sites are temporarily unoccupied to allow colonies to relocate when disturbance occurs. Posting educational signs just prior to the nesting season has been an effective method at limiting human disturbance to colonies of other tern species on beaches (Burger 1989).

Research Needs

Forster's Terns have been studied less than other North American Tern species (Mcnicholl et al. 2001). More research is needed to determine their specific habitat requirements. Additionally, research into stopover locations and winter ecology is needed, especially to determine winter movements (Mcnicholl et al. 2001). Since there is much variability in nesting success between years and individuals may exhibit low site tenacity readily switching breeding colonies, long-term studies of reproductive success on marked birds are needed to determine trends in population numbers and productivity over time.

Habitat

Habitat

In New York, Forster's Terns nest on marsh islands located in bays off the south shore of Long Island (Connor 1988b, McGowan and Corwin 2008, Sommers et al. 2001). They often nest on wrack material that has been been deposited on top of cordgrass stands during flooding and storms (Martin and Zwank 1987). This material is useful because it is elevated higher than the usual high water line and may float during floods (McGowan and Corwin 2008).

Associated Ecological Communities

  • High salt marsh (guide)
    A coastal marsh community that occurs in sheltered areas of the seacoast, in a zone extending from mean high tide up to the limit of spring tides. It is periodically flooded by spring tides and flood tides. High salt marshes typically consist of a mosaic of patches that are mostly dominated by a single graminoid species.
  • Low salt marsh (guide)
    A coastal marsh community that occurs in sheltered areas of the seacoast, in a zone extending from mean high tide down to mean sea level or to about 2 m (6 ft) below mean high tide. It is regularly flooded by semidiurnal tides. The mean tidal range of low salt marshes on Long Island is about 80 cm, and they often form in basins with a depth of 1.6 m or greater.
  • Salt panne (guide)
    A shallow depression in a salt marsh where the marsh is poorly drained. Pannes occur in both low and high salt marshes. Pannes in low salt marshes usually lack vegetation, and the substrate is a soft, silty mud. Pannes in a high salt marsh are irregularly flooded by spring tides or flood tides, but the water does not drain into tidal creeks. After a panne has been flooded the standing water evaporates and the salinity of the soil water is raised well above the salinity of sea-water.

Associated Species

  • Laughing Gull (Leucophaeus atricilla) (guide)
  • Common Tern (Sterna hirundo) (guide)

Range

New York State Distribution

The range of Forster's Terns in New York is highly restricted. The species is known as a breeder in the state only since 1981 (Zarudsky 1981) and only occurs on marsh islands off the south shore of Long Island (Mcnicholl et al. 2001, Sommers et al. 2001, McGowan and Corwin 2008). Significant breeding locations in the state include Jo Co Marsh in Jamaica Bay, and the Cinder Island and Cuba Island groups.

Global Distribution

BREEDING: The range of the Forster's Tern extends from the central Prairie Provinces of Canada (Lake Winnipeg, Manitoba, to southeastern British Columbia) south to southern California, western Nevada, southern Idaho, northern Utah, northern and eastern Colorado, central Kansas, western Nebraska, northern Iowa, northwestern Indiana, to eastern Michigan; along the coast from northeastern Mexico (Tamaulipas), southeastern Texas to southern Alabama; and along the Atlantic coast from Long Island to (rarely) South Carolina. NONBREEDING: The winter range includes central California and Baja California to Oaxaca, Guatemala, and casually to Costa Rica; northern Veracruz to western Florida; Virginia to northern Florida; Bahamas and Greater Antilles.

Best Places to See

  • Hempstead Bay (Nassau County)

Identification Comments

General Description

The Forster's Tern is a medium-sized tern most often occurring in and around marshes. They are white below, pale grey above, with a black cap and mostly orange bill.

Identifying Characteristics

Forster's Terns are a medium-sized tern most often occurring in and around marshes. They measure 33-36 cm (13.0-14.2 in.) in length and weigh 130-190 g (4.6-6.7 oz.). The sexes appear similar (Mcnicholl et al. 2001). The adult breeding plumage is white below, pale grey above, with a black cap and nape. The birds have a mostly orange bill, orange legs, and orange feet. They have a long, deeply forked grey tail with white outer edges. When they are in flight, the upperwing area appears pale due to the grey primaries (long flight feathers that extend along the outer edge of the wings), and the white rump contrasts with the grey back and tail (National Geographic Society 1983). The adult nonbreeding plumage has a black "mask" around the eye and over the ears instead of a black cap. The mask does not reach the nape or rear of the top of the head. The forehead is white, bill is black, and feet are orange (Mcnicholl et al. 2001). Compared to adults, juveniles and first-winter birds have shorter tails and generally more dark color in the wings and darker primaries. Juveniles have a brown cap, dark eye patch, and a faint or absent bar on the shoulder. Calls of Forster's Terns include a hoarse "kyarr" that is lower and shorter than that of Common Terns (Sterna hirundo). They nest in colonies that are widely spaced in marshes (National Geographic Society 1983). Nests can occur as scrapes in the mud or sand with little or no lining, in clumps of vegetation or on floating vegetative mats, or on top of muskrat lodges (Mcnicholl et al. 2001). Clutches usually contain two to three eggs. Less often, they contain one or four, and very rarely, up to six. The background color of the eggs is usually olive to buff or pinkish buff, with many brown spots, small blotches, and crooked lines that often decorate the larger end (Bent 1921, Mcnicholl 1971). The eggs are smooth, but not glossy (Harrison 1979).

Characters Most Useful for Identification

The combination of characterstics that distinguish this species are: a tern with a pale grey back, black cap, orange legs and bill (with a black tip), long legs and bill, and deeply forked tail (National Geographic Society 1999).

Best Life Stage for Proper Identification

Adults in breeding plumage are easiest to identify but juveniles and birds in their winter plumage can also be distinguished from other tern species.

Behavior

Forster's Terns forage aerially over flooded mudflats or calm waters for insects and fish. They may forage alone or in mixed-species foraging aggregations (Schreffler et al. 2010). Pairs are monogamous, at least for the breeding season. They may nest colonially, co-occuring with other Larids including Common Terns (Sterna hirundo) and Laughing Gulls (Larus atricilla). Forster's Terns are territorial during the courtship period. A study of California Forster's Terns found that colonies were attended in roughly equal amounts by males and females, with the females more frequently present at night and the males more frequently present during the day (Bluso-Demers et al. 2010).

Diet

The diet of the Forster's Tern consists mainly of small fish and arthropods (McNicholl et al. 2001).

Best Time to See

Forster's Terns may be observed in NY in the spring, summer, or fall. Breeding individuals are present on Long Island from late May into August. Forster's Terns may appear along the coast or Great Lakes during spring (April into May) or fall migration (mid to late August through November), and are more common in the fall (Levine 1998). They are also found along the lower Hudson River (mostly south of Dutchess County) in the fall , as well (Levine 1998).

  • Active
  • Reproducing

The time of year you would expect to find Forster's Tern active and reproducing in New York.

Similar Species

  • Roseate Tern (Sterna dougallii) (guide)
    Roseate Terns appear similar to Forster's Terns but have a bill that is mostly black with red-orange at the base and reddish-orange feet. The wingbeat of the Forster's Tern is much slower than that of the Roseate Tern (National Geographic Society 1999).
  • Common Tern (Sterna hirundo) (guide)
    Common Terns appear similar to Forster's Terns but have shorter legs, longer wings, and a smaller head. The back is also medium grey compared to the light grey back of the Forster's Tern.

Forster's Tern Images

Taxonomy

Forster's Tern
Sterna forsteri Nuttall, 1834

  • Kingdom Animalia
    • Phylum Craniata
      • Class Aves (Birds)
        • Order Charadriiformes (Gulls, Plovers, and Shorebirds)
          • Family Laridae (Terns, Gulls and Relatives)

Additional Resources

References

American Ornithologists' Union (AOU). 1983. Check-list of North American Birds, 6th edition. Allen Press, Inc., Lawrence, Kansas. 877 pp.

Andrle, R. F., and J. R. Carrol, editors. 1988. The atlas of breeding birds in New York State. Cornell Univ., Ithaca, New York. 551 pp.

Bent, A.C. 1921. Life histories of North American gulls and terns. U.S. Natl. Mus. Bull. 113. Washington, D.C.

Bluso-Demers, J.D., J.T. Ackerman, and J.Y. Takekawa. 2010. Colony attendance patterns by mated Forster's Terns (Sterna forsteri) using an automated data-logging receiver system. Ardea 98:59-65.

Bull, John. 1964. Birds of the New York area. New York: Harper and Row Publications 540 pp.

Bull, John. 1974. Birds of New York State. Doubleday, Garden City, New York. 655 pp.

Burger, J. 1989. Least Tern populations in coastal New Jersey: monitoring and management of a regionally-endangered species. Journal of Coastal Research 5:801-811.

Byrd, M. A., and D. W. Johnston. 1991. Birds. Pages 477-537 in K. Terwilliger, coordinator. Virginia's endangered species: proceedings of a symposium. McDonald and Woodward Publ. Co., Blacksburg, Virginia.

Clapp, R. B., and P. A. Buckley. 1984. Status and conservation of seabirds in the southeastern United States. Pages 135-155 in Croxall et al., eds. Status and conservation of the world's seabirds. ICBP Tech. Pub. No. 2.

Cuthbert, F. J., and M.-Y. Louis. 1993. The Forster's tern in Minnesota: status, distribution, and reproductive success. Wilson Bull. 105:184-187.

Fraser, G.S. 1994. Feeding and nesting behaviors of the Forster's Tern on Lake Osakis, Minnesota. Master's thesis. North Dakota State Univ. Fargo.

Hall, J.A. 1989. Aspects of Forster's Tern (Sterna forsteri) reproduction on cobblestone islands in southcentral Washington. Northwest Sci. 63:90-95.

Harrison, C. 1978. A Field Guide to the Nests, Eggs and Nestlings of North American Birds. Collins, Cleveland, Ohio.

Harrison, H. H. 1979. A field guide to western birds' nests. Houghton Mifflin Company, Boston. 279 pp.

Hartig, E.K., V. Gornitz, A. Kolker, F. Mushacke, and D. Fallon. 2002. Anthropogenic and climate-change impacts on salt marshes of Jamaica Bay, New York City. Wetlands 22:71-89.

Herkert, J. R., editor. 1992. Endangered and threatened species of Illinois: status and distribution. Vol. 2: Animals. Illinois Endangered Species Protection Board. iv + 142 pp.

Kolker, A.S. 2005. The impacts of climate variability and anthropogenic activities on salt marsh accretion and loss on Long Island. Dissertation. State University of New York at Stony Brook. 759 pp.

Levine, E. 1998. Bull's birds of New York State. Comstock Publishing Associates, Ithaca, NY.

Martin, R.P., and P.J. Zwank. 1987. Habitat suitability index models: Forster's Tern (breeding)-- Gulf and Atlantic coasts. U.S. Fish and Wildlife Service Biological Report, no. 82 (10.131). Http://www.nwrc.usgs.gov/wdb/pub/his/his-131.pdf.

McGowan, K.J. and K. Corwin, eds. 2008. The Second Atlas of Breeding Birds in New York State: 2000-2005. Cornell University Press, Ithaca, NY. 688 pp.

Mcnicholl, M.K. 1971. The breeding biology and ecology of Forster's Tern (Sterna forsteri) at Delta, Manitoba. Master's thesis. Univ. of Manitoba, Winnipeg.

Mcnicholl, M.K., P.E. Lowther, and J.A. Hall. 2001. Forster's Tern (Sterna forsteri). In: The Birds of North America, No. 595 (A. Poole and F. Gill, eds.). The Birds of North America, Inc., Philadelphia, Pennsylvania.

Molina, K.C., R. M. Erwin, E. Palacios, E. Mellink, and N. Seto. 2010. Status Review and Conservation Recommendations for the Gull-billed Tern (Gelochelidon nilotica) in North America. Biological Technical Publication BTP-R1013-2010. U.S. Fish and Wildlife Service

Montalto, F.A., and T.S. Steenhuis. 2004. The link between hydrology and restoration of tidal marshes in the New York/ New Jersey estuary. Wetlands 24:414-425.

National Geographic Society (NGS). 1983. Field guide to the birds of North America. National Geographic Society, Washington, DC.

National Geographic Society (NGS). 1999. Field guide to the birds of North America. Third edition. National Geographic Society, Washington, DC. 480 pp.

New York Natural Heritage Program. 2019. New York Natural Heritage Program Databases. Albany, NY.

New York State Breeding Bird Atlas. 1984. Preliminary species distribution maps, 1980-1984. New York State Department of Environmental Conservation, Wildlife Resources Center. Delmar, NY.

New York State Breeding Bird Atlas. 1985. Final breeding bird distribution maps, 1980-1985. New York State Department of Environmental Conservation, Wildlife Resources Center. Delmar, NY.

New York State Department of Environmental Conservation. Checklist of the amphibians, reptiles, birds, and mammals of New York State, including their protective status. Nongame Unit, Wildlife Resources Center, Delmar, NY.

Oberholser, H.C. 1974. The bird life of Texas. 2 vols. Univ. of Texas Press, Austin.

Schreffler L., J.K. Leiser, and T.L. Master. 2010. Costs and benefits of foraging alone or in mixed-species aggregations for Forster's Terns. The Wilson Journal of Ornithology 122:95-101.

Sommers, Laura, D., Daniel L. Rosenblatt and Marcelo J. DelPuerto. 2001. 1998-1999 Long Island Colonial waterbird and Piping Plover Survey. New York State Department of Environmental Conservation, Nongame and Habitat Unit. Delmar, NY and Region 1, Stony Brook, New York.

Spendelow, J. A. and S. R. Patton. 1988. National Atlas of Coastal Waterbird Colonies in the Contiguous United States: 1976-1982. U.S. Fish and Wildlife Service, Biological Report 88(5). x + 326 pp.

Stiles, F. G. and A. F. Skutch. 1989. A guide to the birds of Costa Rica. Cornell University Press, Ithaca, New York, USA. 511 pp.

Terres, J. K. 1980. The Audubon Society encyclopedia of North American birds. Alfred A. Knopf, New York.

Van Rossem, A. J. 1933. Terns as destroyers of birds' eggs. Condor 35:49-51.

Zardusky, J. 1981. Forster's Tern breeding on Long Island. Kingbird 31:212-213.

Links

About This Guide

This guide was authored by: Kelly A. Perkins

Information for this guide was last updated on: June 17, 2011

Please cite this page as:
New York Natural Heritage Program. 2019. Online Conservation Guide for Sterna forsteri. Available from: https://guides.nynhp.org/forsters-tern/. Accessed May 20, 2019.

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