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Montana Field Guide

Montana Field Guides

Caspian Tern - Hydroprogne caspia

Species of Concern
Native Species

Global Rank: G5
State Rank: S2B

Agency Status
USFWS: MBTA
USFS:
BLM: SENSITIVE
FWP SWAP: SGCN2
PIF: 2


 

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Listen to an Audio Sample
Copyright by Borror Laboratory of Bioacoustics, Department of Evolution, Ecology, and Organismal Biology, Ohio State University, Columbus, OH, all rights reserved.
 
General Description
Gull-like in appearance, the Caspian Tern is the largest tern in North America. It has pale gray upperparts, and a white throat, breast, flanks, rump and tail. The all-black cap on the mature adults extends forward to below the eye. Males and females are of like plumage, though the males average slightly larger (Sibley 2000). This species is generally 47 to 54 cm long, with a wingspan of approximately 127 cm. The Caspian Tern has a dark red, stout, rather massive bill, with a dark gray colored tip. The bill on juvenile birds is more orange-red and their upperparts are paler than on the adults.

The vocalization of this species is described as a deep, harsh, heron-like scream "aaayayaum" (Sibley 2000). Several other vocalizations are described as the contact, alarm, gakkering, fish (advertising), and female begging calls (Cuthbert and Wires 1999).

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.

Diagnostic Characteristics
The Caspian Tern is most similar to the Royal Tern, but the latter species, restricted primarily to the coasts, is rarely observed inland. The Caspian is also a larger bird, by approximately 20 percent, and has broader, blunter wings, and a larger head (Cuthbert and Wires 1999). The Caspian's bill is also much darker and thicker. The legs of a Caspian Tern are also slightly longer and thicker and the tail is not notched as deeply as that of the Royal Tern (Cuthbert and Wires 1999). Caspian Terns are distinguishable from other species of terns by their larger size and the blackish undersurface and whitish uppersurface of the outer primaries (Cuthbert and Wires 1999).

Species Range
Montana Range

All Ranges
Summer
Migratory
(Click legend blocks to view individual ranges)

Western Hemisphere Range

 


Observations in Montana Natural Heritage Program Database
Number of Observations: 362

(Click on the following maps and charts to see full sized version) Map Help and Descriptions
Relative Density

Recency

Breeding
(direct evidence "B")


Breeding
(indirect evidence "b")


No evidence of Breeding
(transient "t")


Overwintering
(regular observations "W")


Overwintering
(at least one obs. "w")



 

(Observations spanning multiple months or years are excluded from time charts)



Migration
Caspian Terns begin arriving in late April to mid-May in Montana. Fall migration starts in late August and continues through the end of September. Transient sightings occur throughout the state during spring migration, especially between April and June. The extreme migration dates for this species in Montana are April 16 (1994 at Tiber Dam) and October 8 (1985 near Ravalli) (Reichel 1996).

Habitat
In Montana, the Caspian Tern prefers islands within large lakes or reservoirs, where sandy or stony beaches are used for nesting (Johnsgard 1992). The species has also been noted to utilize rivers, though nesting in this habitat is not documented (Johnsgard 1992, Casey 2000).

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:
    1. 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);
    2. Evaluating structural characteristics and distribution of each ecological system relative to the species' range and habitat requirements;
    3. Examining the observation records for each species in the state-wide point observation database associated with each ecological system;
    4. 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.

    Literature Cited
    • 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.

Food Habits
No specific information regarding food habits for this species exists for the state. Generally, this species eats fishes obtained at the surface of the water by diving from the air; they sometimes feed from the surface like a gull and eat the eggs and young of other terns and gulls (Terres 1980).

Ecology
Caspian Terns occasionally nest on the same island as Double-crested Cormorants in Montana. During the nonbreeding season, Caspian Terns often rest with flocks of other tern species.

Reproductive Characteristics
The Caspian Tern has limited breeding in Montana, and although breeding does occur, specific information on the nesting habits of the species in the state is limited. Colonial nesting is the norm where the species is more common; in Montana, the species is known to nest in low numbers, at times with only one nest at a location (Montana Bird Distribution Committee 2012). Nesting may occur in association with other species, occasionally with Double-crested Cormorant (Phalacrocorax auritus) and gull (Larus) species (Casey 2000). The Caspian Tern is expected to breed at about 10 locations in Montana. These include: Bowdoin National Wildlife Refuge, two islands on Fort Peck Reservoir, Freezout Lake Wildlife Management Area, Canyon Ferry Wildlife Management Area, and Ninepipe National Wildlife Refuge (Reichel 1996). Although this species is rare in the refuge, one breeding record exists for Medicine Lake National Wildlife Refuge (Madden, personal communication). Breeding may take place at Tiber Reservoir (Reichel 1996).

At all known nesting locations, the colonies are relatively small, with upwards of a few dozen pairs nesting at Canyon Ferry Wildlife Management Area. Reproductive data from other areas in the species' range reveals nesting begining by late May or early June. The nest, built by both sexes, is usually a shallow, sparsely lined, or unlined hollow. Clutch size of the smooth, non-glossy sub-elliptical eggs is usually 2 to 3. The eggs sometimes have a finely textured surface, and are light buff in coloration and are generally evenly marked with specks or small blotches of black, brown, olive, and pale gray (Baicich and Harrison 2005). Incubation, by both sexes, lasts 20 to 22 days. Both parents tend young, which leave the nest in a few days, and first fly at 4 to 5 weeks. Parental care (feeding) may extend up to 5 to 7 months after fledging. They nest singly or usually in colonies of up to several thousand pairs (5000+ at Sand Island, Washington).

Management
No management activities specific to Caspian Tern in Montana are documented, however, management recommendations include surveying known nesting colonies on an annual basis to determine status; providing adequate levels of water to protect nesting terns from mammalian predators; managing water levels on lake and river nesting areas to mimic natural seasonal fluctuations; and minimizing human disturbance at nesting colonies during the breeding season (Casey 2000).

References
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Citation for data on this website:
Caspian Tern — Hydroprogne caspia.  Montana Field Guide.  .  Retrieved on , from