Montana Field Guide

Caspian Tern - Hydroprogne caspia

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).

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).

Montana Range

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).

In Montana, the Caspian Tern prefers islands within large lakes or reservoirs, where sandy or stony beaches are used for nesting (Johnsgard 1986). The species has also been noted to utilize rivers, though nesting in this habitat is not documented (Johnsgard 1986, Casey 2000).

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).

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.

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 2003). 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, Pers. Comm. 2003). 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. The number of nesting pairs at this location varies from year to year and may be as high as 51 (1993) or as low as zero (2000) (Jakubowski, Pers. Comm. 2003). 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 1997). 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).

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).