Forster's Tern - Sterna forsteri
The Forster's Tern is a medium-sized, primarily white tern with a black cap and dark eyes. The back and wings are a pale silvery-gray, contrasting with the white of the neck and belly. The primaries and the deeply forked tail on the breeding adult bird are also a pale gray, with the primaries appearing as white as they become worn. During the breeding season, the large bill is orange and tipped in black, and the legs are bright orange or orange-red. In non-breeding plumage the bill is black and the legs are a duller red-brown (McNicholl et al. 2001). During non-breeding season, the primaries are dark silvery-gray and the crown is white with an evident large black patch encompassing and extending behind the eye (Sibley 2000). The bird is approximately 13 inches (33 cm) in length with a 31 inch (79 cm) wingspan.
The common call of this bird is a simple descending "kerrrr
", described as lower and more raspy and wooden-sounding than the Common Tern (Sibley 2000). Sibley (2000) notes the species also has a "kit
" or "kuit
" common call; a begging "kerr kerr kerr
" during courtship; and a very low "zaaaar
" during defensive attack.
For a comprehensive review of the conservation status, habitat use, and ecology of this and other Montana bird species, please see Marks et al. 2016, Birds of Montana.
White wings and underparts give the Forster's Tern a lighter and brighter overall appearance than the Common Tern. The Forster's Tern is also distinguishable from the Common Tern by its longer and stouter bill, longer tail, and more orange, rather than red, colored bill (McNicholl et al. 2001).
Western Hemisphere Range
Observations in Montana Natural Heritage Program Database
Number of Observations:
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Map Help and Descriptions
(direct evidence "B")
(indirect evidence "b")
No evidence of Breeding
(regular observations "W")
(at least one obs. "w")
(Observations spanning multiple months or years are excluded from time charts)
After departing the southern U.S. and Mexico, normal arrival and departure migration dates for the Forster's Tern in Montana are generally May 7 to 24 through the third week in September (Reichel 1996, Sibley 2000). The extreme migration dates for this species are April 28, 1993 at Freezout Lake and September 27, 1958 in Ennis (Reichel 1996). Normal migration periods in Bozeman are May 7 to 12 and September 15 to 19 (Skaar 1969). The normal arrival date in Missoula is May 14, and in Billings it is May 24 (Skaar et al. 1985).
In general, this species is described as a short- to medium-distance migrant. It is present throughout the year in all but the most northerly portions of its breeding range (McNicholl et al. 2001). Dispersal north and south of breeding areas takes place post-breeding. The Forster's Terns migration habits alter from that of the Common Tern by generally being earlier in the spring and later in the fall (McNicholl et al. 2001). The species, which commonly travels in small groups, though larger flocks have been reported, migrates primarily through interior North America.
Large marshes with extensive reed beds or Muskrat houses that provide nesting structures are the preferred breeding habitat for the Forester's Tern. It is also occasionally found along marshy borders of lakes and reservoirs in Montana. The species generally nests colonially, with as many as five nests recorded on one Muskrat house (Johnsgard 1992). Preferred nesting locations include both nesting and foraging sites within close proximity. Saltmarsh bulrush (Scirpus maritimus) was used as nesting substrate at Benton Lake National Wildlife Refuge (Montana Bird Distribution Committee 2012). A study in the Lewistown District of the Bureau of Land Management documented that five of the six sites selected by the Forster's Tern were larger than 100 acres, with emergent vegetation covering more than 25% of the shoreline (Feigley 1997). Four of the nesting sites were on permanent bodies of water, with the remaining two on temporarily flooded sites (Feigley 1997).
Ecological Systems Associated with this Species
- Details on Creation and Suggested Uses and Limitations
How Associations Were Made
We associated the use and habitat quality (common or occasional) of each of the 82 ecological systems mapped in Montana for
vertebrate animal species that regularly breed, overwinter, or migrate through the state by:
- Using personal observations and reviewing literature that summarize the breeding, overwintering, or migratory habitat requirements of each species (Dobkin 1992, Hart et al. 1998, Hutto and Young 1999, Maxell 2000, Foresman 2012, Adams 2003, and Werner et al. 2004);
- Evaluating structural characteristics and distribution of each ecological system relative to the species' range and habitat requirements;
- Examining the observation records for each species in the state-wide point observation database associated with each ecological system;
- Calculating the percentage of observations associated with each ecological system relative to the percent of Montana covered by each ecological system to get a measure of "observations versus availability of habitat".
Species that breed in Montana were only evaluated for breeding habitat use, species that only overwinter in Montana were only evaluated for overwintering habitat use, and species that only migrate through Montana were only evaluated for migratory habitat use.
In general, species were listed as associated with an ecological system if structural characteristics of used habitat documented in the literature were present in the ecological system or large numbers of point observations were associated with the ecological system.
However, species were not listed as associated with an ecological system if there was no support in the literature for use of structural characteristics in an ecological system, even if
point observations were associated with that system.
Common versus occasional association with an ecological system was assigned based on the degree to which the structural characteristics of an ecological system matched the preferred structural habitat characteristics for each species as represented in scientific literature.
The percentage of observations associated with each ecological system relative to the percent of Montana covered by each ecological system was also used to guide assignment of common versus occasional association.
If you have any questions or comments on species associations with ecological systems, please contact the Montana Natural Heritage Program's Senior Zoologist.
Suggested Uses and Limitations
Species associations with ecological systems should be used to generate potential lists of species that may occupy broader landscapes for the purposes of landscape-level planning.
These potential lists of species should not be used in place of documented occurrences of species (this information can be requested at: http://mtnhp.org/requests/default.asp
) or systematic surveys for species and evaluations of habitat at a local site level by trained biologists.
Users of this information should be aware that the land cover data used to generate species associations is based on imagery from the late 1990s and early 2000s and was only intended to be used at broader landscape scales.
Land cover mapping accuracy is particularly problematic when the systems occur as small patches or where the land cover types have been altered over the past decade.
Thus, particular caution should be used when using the associations in assessments of smaller areas (e.g., evaluations of public land survey sections).
Finally, although a species may be associated with a particular ecological system within its known geographic range, portions of that ecological system may occur outside of the species' known geographic range.
- Adams, R.A. 2003. Bats of the Rocky Mountain West; natural history, ecology, and conservation. Boulder, CO: University Press of Colorado. 289 p.
- Dobkin, D. S. 1992. Neotropical migrant land birds in the Northern Rockies and Great Plains. USDA Forest Service, Northern Region. Publication No. R1-93-34. Missoula, MT.
- Foresman, K.R. 2012. Mammals of Montana. Second edition. Mountain Press Publishing, Missoula, Montana. 429 pp.
- Hart, M.M., W.A. Williams, P.C. Thornton, K.P. McLaughlin, C.M. Tobalske, B.A. Maxell, D.P. Hendricks, C.R. Peterson, and R.L. Redmond. 1998. Montana atlas of terrestrial vertebrates. Montana Cooperative Wildlife Research Unit, University of Montana, Missoula, MT. 1302 p.
- Hutto, R.L. and J.S. Young. 1999. Habitat relationships of landbirds in the Northern Region, USDA Forest Service, Rocky Mountain Research Station RMRS-GTR-32. 72 p.
- Maxell, B.A. 2000. Management of Montana's amphibians: a review of factors that may present a risk to population viability and accounts on the identification, distribution, taxonomy, habitat use, natural history, and the status and conservation of individual species. Report to U.S. Forest Service Region 1. Missoula, MT: Wildlife Biology Program, University of Montana. 161 p.
- Werner, J.K., B.A. Maxell, P. Hendricks, and D. Flath. 2004. Amphibians and reptiles of Montana. Missoula, MT: Mountain Press Publishing Company. 262 p.
No food habit information is available for Forster's Tern in Montana. Other source material indicates insects (e.g., dragonflies, caddisflies) are caught in the air or snatched off the surface of the water (e.g., dead beetles) while the bird is in flight. The Forster's Tern also dives into water for fishes, mainly submerging the bill and a portion of the head, though sometimes the entire body is submerged below the surface of the water (Terres 1980, McNicholl et al. 2001).
Forster's Terns are usually found in small, loose colonies in Montana. Little other ecological data is available from within the state. However, information provided from other states in the species' range states that during the non-breeding season, the Forster's Tern can be found singly or in small loose groups.
Limited information is available on disease and parasites common in Forster's Tern. In a Colorado study, 9 of 10 were infected with the fluke Diplostomum spathaceum (Trematoda) and several lice species (Actornithophilus funebre, Philopterus melanocephalus, and Saemundssonis parvigenetalis) (McNicholl et al. 2001).
Forster's Terns nest in Montana from mid-May through mid-August, though little detailed information is available on the timing of reproduction for this species in the state (Reichel 1996). Forster's Terns were observed on the nest as early as June 1, 1995, and reports in North Dakota indicate newly hatched young in late June and early July (Reichel 1996).
Fewer than 500 breeding pairs are anticipated in Montana, with nesting occurring as single pairs or colonies up to 60 pairs (Reichel 1996, Montana Bird Distribution Committee 2012). A study performed in the Lewistown District of the Bureau of Land Management found Forster's Terns nesting from one pair up to 20, depending upon location and available habitat (Feigley 1997). Most reproductive information comes from sources in other areas of the species' range. Nests are most frequently found on mats of floating vegetation or Muskrat houses; in these situations, the nest is lined with grass and reeds (Johnsgard 1979, Godfrey 1986). Occasionally Forster's Terns will nest on islands or beaches like Common Terns, using a lined depression in the mud or sand (Johnsgard 1979, Ehrlich et al. 1988). At times, nests will be very close together on a favored site, such as a Muskrat house, where up to five nests have been reported together (Johnsgard 1979).
Forster's Terns produce eggs from late May to mid-June. Both sexes incubate the clutch of usually 3 to 4 eggs for about 23 to 24 days. The eggs are subelliptical to oval, smooth, non-glossy and very pale, tinted olive or cream, spotted or speckled in brown, blackish-brown, or gray and average 32 x 23 mm (Baicich and Harrison 2005). The semi-precocial young are tended by both adults until capable of flight, fledge at 3 to 4 weeks, and remain with the parents well into the fall (Byrd and Johnston 1991). The Forester's Tern often renests if the first nest is lost; this often occurs at coastal nesting sites as a result of tidal flooding. They nest in loose colonies or singly, with some colonies ranging in size from less than 500 (Atlantic coast) to up to several thousand (Louisiana) (Spendelow and Patton 1988).
No management activities in Montana specific to Forster's Tern are documented. However, recommendations on surveying techniques stress that limited time should be spent at a colony particularly just before egg-laying and just after hatching; the prior, because of the likelihood of desertion of the colony, and the latter, to avoid causing mortality of young chicks (Reichel 1996).
- Literature Cited AboveLegend: View Online Publication
- Baicich, P.J. and C.J.O. Harrison. 2005. A guide to the nests, eggs and nestlings of North American birds. Second edition. Academic Press, New York.
- Byrd, M.A. and D.W. Johnston. 1991. Birds. In: K. Terwilliger, coord. Virginia's endangered species: proceedings of a symposium. p. 477-537. McDonald and Woodward Publishing Company, Blacksburg, Virginia.
- Ehrlich, P., D. Dobkin, and D. Wheye. 1988. The birder’s handbook: a field guide to the natural history of North American birds. Simon and Schuster Inc. New York. 785 pp.
- Feigley, H. P. 1997. Colonial nesting bird survey on the Bureau of Land Management Lewistown District: 1996. Unpublished report, U.S. Bureau of Land Management, Lewistown, Montana.
- Godfrey, W. E. 1986. The birds of Canada. Revised edition. National Museum of Natural Sciences, Ottawa. 596 pp.
- Johnsgard, P.A. 1979. Birds of the Great Plains: breeding species and their distribution. University of Nebraska Press, Lincoln. 539 pp.
- Johnsgard, P.A. 1992. Birds of the Rocky Mountains with particular reference to national parks in the northern Rocky Mountain region. Lincoln: University of Nebraska Press. xi + 504 pp.
- Marks, J.S., P. Hendricks, and D. Casey. 2016. Birds of Montana. Arrington, VA. Buteo Books. 659 pages.
- Reichel, J. D. 1996. Preliminary colonial nesting bird survey on the Bureau of Land Management Lewistown District: 1995. Unpublished report, U.S. Bureau of Land Management, Lewistown, Montana.
- Sibley, D.A. 2000. The Sibley guide to birds. National Audubon Society and Alfred A. Knopf, Inc., New York, NY. 544 pp.
- Skaar, P. D., D. L. Flath, and L. S. Thompson. 1985. Montana bird distribution. Montana Academy of Sciences Monograph 3(44): ii-69.
- Skaar, P.D. 1969. Birds of the Bozeman latilong: a compilation of data concerning the birds which occur between 45 and 46 N. latitude and 111 and 112 W. longitude, with current lists for Idaho, Montana, Wyoming, impinging Montana counties and Yellowstone National Park. Bozeman, MT. 132 p.
- 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.
- Terres, J.K. 1980. The Audubon Society encyclopedia of North American birds. Alfred A. Knopf, New York. 1109 pp.
- Additional ReferencesLegend: View Online Publication
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- American Ornithologists Union. 1983. Checklist of North American birds, 6th Edition. 877 PP.
- American Ornithologists’ Union [AOU]. 1998. Check-list of North American birds, 7th edition. American Ornithologists’ Union, Washington, D.C. 829 p.
- Bergman, R. D., P. Swain, and M. W. Weller. 1970. A comparative study of nesting Forster's and black terns. Wilson Bull. 82:435-444.
- Casey, D. 2000. Partners in Flight Bird Conservation Plan Montana Version 1.0. Montana Partners in Flight. Kalispell, Montana.
- Casey, D. 2000. Partners in Flight Draft Bird Conservation Plan Montana. Version 1.0. 287 pp.
- Casey, D. 2004. Coordinated bird monitoring in Montana - special habitat/species monitoring: wetlands and colonial nesters. Montana Bird Conservation Partnership and University of Montana. pp 12 plus appendix.
- Confluence Consulting Inc. 2011. Montana Department of Transportation Wetland Mitigation Monitoring Reports (various sites). MDT Helena, MT.
- Cuthbert, F. J., and M.-Y. Louis. 1993. The Forster's tern in Minnesota: status, distribution, and reproductive success. Wilson Bull. 105:184-187.
- Davis, C.V. 1961. A distributional study of the birds of Montana. Ph.D. dissertation. Oregon State University, Corvallis. 462 pp.
- Hand, R. L. 1969. A distributional checklist of the birds of western Montana. Unpublished. Available at Mansfield Library, University of Montana, Missoula.
- Lenard, S. 2006. Birds of Blaine County, Riparian Point Count Surveys 2005. Report to the Bureau of LandManagement, Havre Field Station, Havre, Montana. Montana Natural Heritage Program, Helena, MT. 16pp.plus appendices.
- Lenard, S., J. Carlson, J. Ellis, C. Jones, and C. Tilly. 2003. P. D. Skaar’s Montana bird distribution, 6th edition. Montana Audubon, Helena, MT. 144 pp.
- Mcnicholl, M.K., P.E. Lowther, and J.A. Hall. 2001. Forster's Tern (Sterna forsteri). Species Account Number 595. The Birds of North America Online (A. Poole, Ed.). Ithaca, NY: Cornell Laboratory of Ornithology; Retrieved 3/25/2008 from The Birds of North America Online database
- Montana Bird Distribution Committee. 2012. P.D. Skaar's Montana bird distribution. 7th Edition. Montana Audubon, Helena, Montana. 208 pp. + foldout map.
- Montana Bird Distribution Committee. 1996. P. D. Skaar's Montana Bird Distribution, Fifth Edition. Special Publication No. 3. Montana Natural Heritage Program, Helena. 130 pp.
- Montana Bird Distribution Online Database. 2001. Helena, Montana, USA. April-September 2003.
- Montana Dept. of Fish, Wildlife and Parks. Region Four., 1996, Draft Environmental Analysis for Weed Management.
- Scharf, W.C. and G.W. Shugart. 1984. Distribution and phenology of nesting Forster's Terns in eastern Lake Huron and Lake St. Claire. Wilson Bull. 96(2): 306-309.
- Sibley, D. 2014. The Sibley guide to birds. Alfred A. Knopf, New York, NY. 598 pp.
- Stewart, R.E. 1975. Breeding birds of North Dakota. Tri-College Center for Environmental Studies, Fargo, North Dakota. 295 pp.
- U.S. Forest Service. 1991. Forest and rangeland birds of the United States: Natural history and habitat use. U.S. Department of Agriculture, Forest Service Agricultural Handbook 688. 625 pages.
- Additional Sources of Information Related to "Birds"