The largely migratory Forster’s Tern occurs almost exclusively in North America, where it breeds in a variety of marshy habitats. Fish are the Forster’s Tern’s primary food source, and they use shallow plunge-dives in which their head is submerged to capture fish.
Like other terns, Forster’s Terns aggressively defend their nests against intruders. Dive-bombing swoops can be expected if a human approaches a nest colony. Nests can be a simple scrape on the ground, or a floating platform of vegetation.
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Description of the Forster’s Tern
The breeding adult Forster’s Tern is a medium sized tern with white underparts, orange legs, a pale gray mantle, black cap, mostly white primaries, forked tail, and an orange bill with a black tip. Length: 13 in. Wingspan: 31 in.
Compare Forster’s Tern on the left with Common Tern on the right. Dark bar on the side of the wing is a good mark on winter-plumaged Common Terns.
Seasonal change in appearance
Winter adults have a black bill and a white forehead and crown, with a black patch behind each eye.
Immatures resemble winter adults but have browner upperparts.
Forster’s Terns inhabit lakes, marshes, bays, and beaches.
Forster’s Terns eat fish, insects, and crustaceans.
Forster’s Terns forage by plunging into the water from above to capture prey.
Forster’s Terns have a widespread and disjunct breeding range including parts of the Gulf Coast, northeastern U.S., Great Lakes, southern Canada, and the northwestern U.S. They winter along the lower Pacific and Atlantic Coasts, as well as the Gulf Coast and points south. The population has declined in recent decades.
Bent Life History
Visit the Bent Life History for extensive additional information on the Forster’s Tern.
The shape of a bird’s wing is often an indication of its habits and behavior. Fast flying birds have long, pointed wings. Soaring birds have long, broad wings. Different songbirds will have a slightly different wing shape. Some species look so much alike (Empidonax flycatchers) that scientists sometimes use the length of specific feathers to confirm a species’ identification.
Wing images from the University of Puget Sound, Slater Museum of Natural History
Forster’s Terns do not migrate as far as Common Terns, leaving many to winter in the U.S.
Forster’s Terns are not seen offshore nearly as often as Common or Arctic Terns.
The typical call is a descending “krrrr.”
- Common Tern
Common Terns have grayer underparts as adults, and darker primaries in all plumages. They also retain more black on the head in nonbreeding plumage.
The Forster’s Tern’s nest is a platform of grasses and reeds placed on a mat of floating vegetation or on a muskrat house.
Number: Usually lay 3 eggs.
Color: Buffy or olive with darker markings.
Incubation and fledging:
The young hatch at about 23-25 days, but their development is not well known.
Bent Life History of the Forster’s Tern
Published by the Smithsonian Institution between the 1920s and the 1950s, the Bent life history series of monographs provide an often colorful description of the birds of North America. Arthur Cleveland Bent was the lead author for the series. The Bent series is a great resource and often includes quotes from early American Ornithologists, including Audubon, Townsend, Wilson, Sutton and many others.
Bent Life History for the Forster’s Tern – the common name and sub-species reflect the nomenclature in use at the time the description was written.
STERNA FORSTERI (Nuttall)
Although differing from the common tern in several details and in its habits, the Forster’s tern so closely resembles it in general appearance that it is not to be wondered at that the species remained so long unrecognized, and that, even after its discovery,’ its distribution and habits were so little understood. Audubon (1840) described and figured this species, in its winter plumage under the name Sterna kavelli, but apparently never recognized it in its spring plumage. Doctor Coues (1877) says of it:
Swainson and Richardson described it as the common tern; Wilson did not know it at all; and Audubon only became aware of it in the imperfect plumage which he described as “kavelli.” Nuttall doubtingly gave it a name upon the strength of Richardson’s description. Mr. Lawrence, In 1858, was the first to elucidate its characters satisfactorily, while it was not until the appearance of my paper that its changes of plumage became known.
But even he, with all his wide field experience, was entirely ignorant of its breeding range, saying: It breeds In the interior of British America, and very abundantly, to judge from the great numbers of eggs from that region I have seen. It may yet be found to nest on or near the northern tier of States.
It is now known, of course, to have a very wide breeding range, as far east as Virginia, as far south as Texas, and as far west a~ California.
It seems to me that the name marsh tern might much more properly have been applied to this species than to the gull-billed tern, for Forster’s tern is, during the breeding season at least, essentially a bird of the marshes, whereas the gull-billed tern shows a decided preference for sandy beaches.
Spring: Rev. P. B. Peabody (1896) says that these terns arrive on their breeding grounds at Heron Lake, Minnesota “about April 7,” and describes their behavior as follows:
Terns creep, scout-like, on the wing, along the thawing shores. Then, as heat and wind wave melt and crush the ice bonds of the lake, the tern speedily assumes the hawk-like (or swallow-like) habit, wandering fitfully over the newly released waters, with eye alert, beak pointing downward, and with many a shrill but cheery cry of self-gratification or of brotherly good will. He knows not fear. As one rows among the innumerable “copes” of rush and flag, bent on reaching the Mallard’s feeding ground, a skIrmish line of terns will wander by, 20, 15, 10 feet overhead, furiously, without swerving a wing breadth from their course. The one or two that are passing eye curiously the dumb decoys in the boat’s belly, and then saunter on with a rattling jeer of derision at the hunter who toils at the oar, and who, unlike the tern, Is never quite sure of his game. But, then, our black-capped Jaeger hunts all day.
Nesting: I first found this species breeding on Wreck Island, off the coast of Virginia, on June 28, 1907, where we discovered a colony of about 50 pairs. This and the other large islands in the group are much like Cobb’s Island, consisting of long, wide beaches on the outer, or ocean, side, flat and sandy in some places or piled high with accumulated oyster shells in others. Back of the beaches, on the shore side, are extensive salt meadows or marshes, intersected by numerous creeks and dotted with small ponds or mud holes. On the outer beaches we found breeding colonies of black skimmers, common and gull-billed terns, and over the marshes were scattered nests of laughing gulls and clapper rails. Our attention was first attracted to the Forster’s terns by their harsh grating cries, as they flew out to meet us while exploring one of the creeks in our skiff. We finally located the colony, by the actions of the birds, just beyond the long grass, which grew thickly along the banks of the creek, and found the nests thickly scattered along the drifted piles of dead sedges, which the high tides had floated off the marsh and deposited in long rows close to the tall-growing sedges. The nests were so close together that I counted 12 nests in a space about 10 yards long by 3 yards wide. One nest was placed within 3 feet of a clapper rail’s nest. The nests were mostly large and elaborate structures, remarkably well built, and reminding me of the nests of Franklin’s gulls. They consisted of large piles of dead sedges and grasses, surmounted by neat little nests, deeply hollowed, with well-rounded and compactly woven rims. They usually measured between 20 and 30 inches in diameter, the smallest one measured being 16 inches at the base; the cup-shaped portion, or nest proper, measured from 7 to 8 inches outside and from 4 to 5 inches inside in diameter; the inner cavity was from 1 to 1 1/2 inches deep and was neatly lined with split reeds and grasses. On the whole, the nests looked like works of art when compared with the slovenly nests built by other species of terns. Most of the nests contained three or four eggs. but many sets of five were found and a few nests held newly hatched young.
In the Breton Island reservation, off the coast of Louisiana, I found two breeding colonies of Forster’s terns. On Battledore Island a colony of about 30 pairs were nesting in a corn pact group on a strip of drift seaweed which had washed up over a marsh and lodged against the tall grass and ” black mangrove” bushes sur rounding it. Numerous Louisiana herons were nesting in the “mangroves” and vast colonies of breeding, laughing gulls and black skimmers occupied the remainder of the island. The terns’ nests were similar to those seen on the Virginia coast, described above, and the eggs were nearly all hatched. The following day (June 22, 1910) I found a much larger colony of this species, consisting of about a thousand pairs, on Hog Island, a few miles distant. This island had been broken up into several sections by the washing away of beaches and soil, leaving large areas of swampy salt meadows, overgrown with long grass and extensive thickets of “black mangrove ” bushes. Louisiana herons were breeding in the “mangroves” and laughing gulls and Forster’s terns on the marshes. Most of the tern’s eggs had hatched and some of the young were nearly grown.
In Texas the nesting habits of this species seem to be entirely different. Mr. George B. Sennett (1878) on May 16 found it breeding in the salt marshes on the Rio Grande.
On the same low and nearly submerged island where we found the eggs of stilt, Himantopus nigiicollis, and some hundred yards or more distant, was a group of these terns upon the ground near their eggs. When we approached them they commenced screaming and flying about in great distress. They had only fairly begun to lay, as no set was complete. One or two eggs were all that any nest contained, and some were not occupied. The nests were situated farther away from the water than the stilts, but still where the mud was wet, and consisted simply of a patting-down of grasses and soil Into a shallow, saucer-shaped depression.
Mr. N. S. Goss (1891) found them “breeding in numbers on the small islands in Nueces Bay, Texas, as early as the 1st of April. The birds at such times are very noisy, and, as their nesting places are approached, their hoarse notes as they circle close overhead are almost deafening. Nest, a hollow, worked out in the sand, and broken shells, and lined with grasses.”:
Still another style of nesting seems to prevail in the western States. Mr. Robert B. Rockwell (1911) gives an interesting account of a colony of Forster’s terns in the Barr Lake region of Colorado, saying:
On May 24, 1907, a week after the first eggs were found, the breeding colony was in full swing, and we were surprised to find a number of nests containing complete sets, which had been built by the birds upon floating masses of decaying cat-tails. These structures were all made entirely of dead cat-tail stalks, and while they varied greatly In size and bulk, the general plan of construction was the same in all, being a compact pile of material of irregular outline, apparently floating on the surface of the water (although in reality the nests were supported by masses of dead cat-tails beneath the surface of the water), and were very conspicuous owing to the lack of concealing vegetation. The eggs were deposIted In the center of the pile in a neat depression, which was lined with small bits of the same material. The bottom of the cavity was, In every instance, well above the surface of the water (usually from 2 to 6 Inches), and the nest cavities were entirely free from moisture. Most of these nests were built in comparatively open water almost waist deep, and about 30 yards from shore. On the date mentioned (May 24) 15 nests were examined, about a third of which were constructed by the birds as described, while the remaining two-thirds were the usual depressions in muskrat houses. The majority of these nests contained three eggs, but a few of them held only one and two, and one nest contained five.
The habit of nesting on old and partially dilapidated muskrat houses seems to be common at many places throughout the lakes and swamps of the interior. In such situations little, if any, nest is built, and sometimes two, or even three, sets of eggs are found on one house. Usually the nest consists merely of a hollow excavated in the half-decayed vegetable rubbish, but sometimes a few reeds, rushes, or bits of grass, brought from a distance, are added to line the cavity or build up a slight rim around it.
Mr. Milton S. Ray (1903) describes a breeding colony of this species in Lake Valley, California, in which the nests were built in various situations. The majority were built up of dry tules where the water is about 5 feet deep. When freshly built of green tules the nest formed a pretty picture. They were placed among tail, thick tules or marsh grass and pond lilies at their edge. Great difference existed in the nests, some being elaborate structures, while others were scantily made and placed on soggy masses of dead tules or floating logs.
In Washington, according to Dawson (1909), these terns make use of the old nests of the western grebe and sometimes even appropriate an occupied nest of the latter. He shows a photograph of such an occupied nest, and says he has “seen others in which the eggs of the rightful owner were nearly buried under a little turret of dried reeds, upon which the tern had been allowed to place her full complement of eggs.”
Eggs: In spite of the fact that the breeding season is much prolonged, and that early and late sets of eggs are often found, the Forster’s tern doubtless raises only one brood in a season. The normal set consists of three eggs, sometimes only two; sets of four eggs are common, sets of five are not rare, and even sets of six have been reported. These larger sets usually, if not always, show evidences of having been laid by more than one female, either in the shape, color, or extent of incubation in the eggs.
The eggs of Forster’s tern are practically indistinguishable from those of the common tern. In shape they are ovate, short ovate, or elongate ovate. The shell is thin, smooth, and without luster. The ground color varies from ‘tawny olive” or “cinnamon ~ to cartridge buff or ” pale olive buff.” The markings are usually rather small spots, more or less evenly distributed, but often these are congregated to form a ring on or near the larger end; many eggs are boldly and handsomely marked with large blotches or ~r regular scrawls. These markings are in the darker shades of brown, such as “chestnut brown,” “burnt umber,” or “seal brown.” Some eggs have underlying blotches of lighter shades, such as “tawny russet” or “hazel.” Nearly all eggs, especially the lighter types, show spots or blotches of various shades of lilac or lavender grays. Where there are markings of several different colors on the same egg the effect is often very pretty. The measurements of 65 eggs, in the United States National Museum, average 43 by 31 millimeters; the eggs showing the four extremes measure 48 by 29.5, 43 by 32.5, 39 by 31 and 42 by 28.5 millimeters.
Young: The period of incubation is 23 days, and probably both sexes incubate. The young remain in the nest for a few days, until they are strong enough to run about or swim, when they become very lively and pugnacious. They take to the water readily and soon become expert at running or swimming about the marsh and hiding in the grass. They are fed by their devoted parents until fully grown and able to fly.
Plumage: The downy young is quite different from that of the common tern. The upper parts vary from light “clay color,” through ” cinnamon buff to ” pinkish buff,~~ shading off to paler shades of the same color below, paling on the breast and belly almost to white, and darkest on the throat, which is “wood brown” or “drab” in some specimens, but never so dark as in the common tern. The upper parts are heavily spotted or streaked with black or “blackish brown,” less heavily on the head and more heavily on the back, where these markings are confluent into great blotches or longitudinal bands. This color pattern is well adapted to conceal the chick among the lights and shadows of the marsh grass where it hides.
The juvenal plumage, which is acquired by the time that the young bird has attained its growth, is also quite distinctive and matches the surroundings in which the young bird lives with a heavy suffusion of dark browns on the upper parts. In this plumage the pearl gray of the back and scapulars is almost wholly concealed by the brown terminal portions of the feathers, which are “clay color” or “cinnamon buff,” centrally clouded or barred with “snuff brown,” or “burnt umber”; the top of the head is nearly uniform “snuff brown”; the sides of the neck are heavily clouded, and the forebreast and rump are lightly clouded with the same color, which also shows on the tips of the lesser wing-coverts, some of the greater wingcoverts, and the rectrices; a conspicuous black patch surrounds the eyes and covers the auriculars. As the season advances all these brown markings fade or wear off to produce the first winter plumage; in this plumage the rump and breast become pure white, the browns on the upper parts gradually disappear or leave only traces of the buffy edgings in the shape of transverse bars; a partial molt of the body plumage also takes place at this time. Young birds, in their first winter plumage, may be distinguished from adults by their shorter and less deeply forked tails with some brownish mottling, and by their darker primaries, which are less silvery and have the white spaces more sharply contrasted with the black.
A complete prenuptial molt in February and March produces the first nuptial plumage, which is usually indistinguishable from the adult. Some young birds in nuptial plumage have wings somewhat like those of the first winter plumage; others renew the first winter plumage of the head; but, as a rule, young birds become indistinguishable from adults when 9 or 10 months old.
Adults have two complete molts – a prenuptial in February and March and a postnuptial in August – and two distinct plumages. The adult winter plumage, which Audubon described as Sterna havelli, is quite different from the well-known spring plumage. The crown is usually largely and sometimes wholly white, though dusky spots are often scattered through it, and there is a more or less distinct nuchal crescent of dusky tipped feathers; there is a distinct black space, including the eye and the ear coverts; the lateral tail feathers are shorter than in the spring, and the primaries, when freshly grown, are beautifully silvered.
Food: Being so largely a bird of the marshes, Forster’s tern feeds less on fish and has a more varied bill of fare than the other terns. It may be seen catching insects on the wing, as well as hovering over the pools, its bill pointing straight downward, looking for tiny morsels of food on the surface. It sometimes makes a diving plunge into the water, but more often it drops down lightly or swoops gracefully along the surface, picking up its food without wetting its plumage. Rev. P. B. Peabody (1896) notes that “the first apparent spring-time food consists of dead fish and frogs and other aquatica that have perished in the winter ice, and are being revealed as the latter melts beneath the sun.” Mr. W. L. Dawson (1909) says:
When the Insects are flying well the terns prefer to hawk. Dragon flies and caddis flies are favorite quarry, and in pursuit of the latter the birds will often rise to a height of several hundred feet.
The birds shot in Louisiana by Audubon (1840) “were engaged in picking up floating coleopterous insects.”:
Behavior: I have never been able to discover anything distinctive in the flight of Forster’s tern; it is as light and graceful as that of the common tern, which it closely resembles in every particular. Although quite different in the fall, the two species can not be easily distinguished in the spring; the white breast of the former is often obscured by shadow, the slight difference in size inappreciable, and the only field mark of consequence is the slightly longer tail of forsteri, which is not very conspicuous.
The voice, however, is quite distinctive and usually makes identification easy and certain. The cry of the young bird in juvenal plumage, as we heard it in the Manitoba marshes, is a shrill, high-pitched squeal, quite different from the notes of other terns or gulls. I noted at the same time the call of the adult as harsh and grating, on a low key and sounding like “tza-a-ap.” Elsewhere in my notes I find that I have described the same note as ” zreep” or” zrurrrr a rasping, nasal, buzzing sound, suggesting the well-known note of the nighthawk. It also utters on rare occasions a soft “wheat, wheat,” like the common tern. On the Virginia coast the prevailing notes were the characteristic, harsh, grating cries described above; but I also heard here a shrill, peeping note, “pip, pip, pip, pip, pip,” rapidly given.
Mr. Peabody (1896) condemns Forster’s tern as a “mis-avian spirit,” saying:
While sociable among his kind, and, to them, moderately good-tempered (except In the breeding time), he Is radically hostile to all other birds. A veritable Ishmael among the waterfowl, his spirit, both of courage and of mean cowardice, is never so clearly portrayed as when, by mutual encroachment upon favorable waters, many species other than those of his feather flock together.
Evidently the tern has many foes. The Franklin’s gull is his arch enemy; the muskrat and the mink undoubtedly do away with many eggs, while the character of this tern himself Inclines me to think that he occasionally plays the cannibal.
Mr. Rockwell (1911) cites the following incident:
A few black-crowned night herons were nesting among the terns, and one unfortunate youngster, unable to fly, who deserted his nest at our approach, took refuge on a tern’s nest, where he was promptly attacked by half a dozen of the birds, and although twice as large as his assailants, was knocked down repeatedly by well-directed blows of the birds’ wings, until he finally sought safety in the water.
Winter: As Forster’s tern is somewhat hardier than others of its genus, the fall migration is more prolonged and it winters farther north. Migrants begin to arrive on the Carolina coasts as early as August and linger until late in the fall, wintering regularly in South Carolina and occasionally farther north. In Florida it is a very common winter resident on inland waters and on the coast.
Breeding range: Temperate North America, mainly within the United States, at widely scattered localities. East to western Ontario (Port Maitland, near the east end of Lake Erie) and the coast of Virginia (Northampton County). South to the coast of Louisiana (various islands), southern coast of Texas (Refugio to Cameron counties), central Colorado (Barr Lake region), northern Utah (Great Salt Lake region) and central California (Merced County). West to the central valleys of California (San Joaquin and Sacramento Valleys), central southern Oregon (Klamath Lakes), and central Washington (Douglas County). North to central Alberta (60 miles southeast of Edmonton), and central Manitoba (Lake Winnipegosis).
Breeding grounds protected in the following national reservations: In Louisiana, Breton Island and Shell Keys; in Oregon, Kiamath Lake and Malheur Lake.
Winter range: From the coast of South Carolina and the Gulf coasts of Florida, Louisiana, and Texas southward to Brazil (Pernambuco. From southern California (San Diego region) southward along the west coast of Mexico to Guatemala.
Spring migration: Early dates of arrival: Virginia, Smith’s Island, May 10; New Jersey, Five Mile Beach, April 26, and Long Beach, May 14; Ohio, Cincinnati, May 4; Ontario, May 22; Kansas, Emporia, April 18; Illinois, Chicago, May 6; Minnesota, Heron Lake, April 7; Manitoba, Oak Point, May 17; California, Stockton, April 17, and Monterey, May 10.
Fall migration: Early dates of arrival: Lower California, San Jose del Cabo, September 29; Guatemala, Lake Duenas, October 28. Late dates of departure: Ontario, Toronto, October 19; Minnesota, Heron Lake, October 14; California, Monterey, September 23.
Casual records: Stragglers in summer and fall have been taken as far east as Massachusetts (Ipswich, September, 1870, and Monomoy Island, October 2, 1880).
Egg dates: Virginia: Twenty-eight records, May 30 to July 12; fourteen records, June 5 to 28. Manitoba: Twenty-one records, June 7 to July 12; eleven records, June 8 to 21. Utah: Nineteen records, June 5 to July 3; ten records, June 11 to 20. California: Fifteen records, May 26 to July 12; eight records, May 27 to June 15.