Common Tern photo by Nick Anich
Right now terns are moving into the state and will soon be nesting in colonies at waterbodies across Wisconsin. Read more to learn which species are in your area, and how to find them. Note that we already profiled Black Tern.
Because breeding only occurs in colonial situations, seeing these species in your block is not necessarily indicative of local breeding because they range widely when foraging, and therefore codes like H, P, and CF are generally not useful for these species. Similarly, FL, and FY codes away from nest sites are not reliable because these species disperse widely once fledged.
Forster’s Tern
Forster’s Tern photo by Joel Trick
Profile: State-endangered species. Forster’s are typically associated with lake, bay, or impoundment islands of emergent vegetation (cattail, roundstem bulrush, phragmites, sagittaria, bur-reed) surrounded by open water, or in a few cases extensive marshes not surrounded by open water. Primarily forage for small fish/minnows by diving within 30 m of water surface, usually in shallower water.
WBBA I Breeding Range – Forster’s Tern
Known Colony Sites: Forster’s occupy sites in the Winnebago Pool lakes, Horicon Marsh, Lake Puckaway, Hope Marsh, Big Muskego Lake, Green Bay, and formerly at Rush Lake and cattail-sagittaria stands along the Mississippi River.
Arrival: Late April-early May. Breeding: Nests w/2-3 Eggs, occasionally 4, rarely 5: mid-May to late July (renests). Incubation: 23-24 d/21-28 d; Fledging: 26-28 d/22-29 d.
When To Survey: 15 May-1 July. But if you suspect a colony is present, don’t attempt to enter the colony. If it is a new colony not listed above, please report it to Nick Anich or Ryan Brady, and we will alert appropriate DNR staff, who will survey the site to obtain an exact number of nesting pairs.
Focal Habitat: Large inland lake marshes in east-central and southeastern WI, Lower Green Bay cattail marshes, and (possibly) saggitaria–cattail marsh sites along the Mississippi River.
Code Guidance: When near a suspected colony (indicated by a number of terns entering and leaving a site), use N for “probable nest/colony site,” T when an adult dive-bombs you in territorial defense, C when an adult presents a minnow to another adult (typically at or near the colony site), or copulation is observed, and ON for birds sitting on nests. Terns may forage or loaf on beaches miles away from their colony site, and fledged young can disperse widely, so codes like P, CF, FL, and FY are discouraged in most cases unless you are aware of a nearby colony.
Other Species: Be aware of and document other marsh birds present, especially Yellow-headed Blackbird, Sora, Virginia Rail, Redhead, Red-necked Grebe, Common Gallinule, Least Bittern, American Bittern.
Confusing Species and Molting Adults/Fledglings: Breeding Forster’s Terns (FOTE) and Common Terns (COTE) are most often confused with each other. FOTE is the tern “with frosty wing tips”—whitish primaries compared to darker COTE primaries. Observe orange beak with black tip in FOTE compared to reddish COTE bill and black tip. Note the tail markings. COTE has a whitish tail with dark outer margin. FOTE tail appears more gray overall. It’s possible (uncommonly to rare) you might also encounter an Arctic Tern during migration; this bird is very similar in appearance to an adult COTE, except that note the Arctic Tern’s white cheeks contrast markedly with its gray throat and breast, and its shorter bill is usually blood-red to the tip. Chances are in July/August you will observe FOTE, COTE, and/or Black Tern fledged young and/or molting adults on a lake, marsh, or impoundment. Note at this time of the year marked differences in adult appearances. Fledgling and fall adult FOTEs can be readily told apart from their COTE counterparts because they have a black mask through the eye and ear, but not around nape as with the COTE. In mid-summer, molting adult Black Terns appear mottled, when the black body is largely replaced by white, and the head has a pied appearance. BLTE may be confused with molting or fledged FOTE or COTE, though the fledgling FOTE and COTE have a brownish or grayish appearance.
More information about Forster’s Tern:
All About Birds
eBird Range Map
Birds of North America Account (subscription required)
Common Tern
Common Tern photo by Nick Anich
Profile: State-endangered species. Common terns are typically associated with dredge spoil or constructed islands on Great Lakes and large inland lakes. They primarily forage for small fish/minnows by diving as high as 12 m from water surface.
WBBA I Breeding Range – Common Tern
Known Colony Sites: Common Terns have colonized only 5 sites to date, two on Lake Superior, one on Lake Butte des Morts, rafts on Lake Puckaway, and rafts in Lower Green Bay.
Arrival: mid-April to June. Breeding: Nests w/1-3 eggs, rarely 4-5: late May to early August (renests). Incubation: 23-24 d/21-28 d; Fledging: 26-28 d/22-29 d.
When To Survey: 1 June-1 July. But if you suspect a colony is present, don’t attempt to enter the colony. If it is a new colony not listed above, please report it to Nick Anich or Ryan Brady, and we will alert appropriate DNR staff, who will survey the site to obtain an exact number of nesting pairs.
Focal Habitat: Sparsely vegetated dredge spoil islands and small “man-made” island sites on the Great Lakes and on large interior lakes.
Code Guidance: When near a suspected colony (indicated by a number of terns entering and leaving a site), use N for “probable nest/colony site,” T when an adult dive-bombs you in territorial defense, C when an adult presents a minnow to another adult (typically at or near the colony site), or copulation is observed, and ON for birds sitting on nests. Terns may forage or loaf on beaches miles away from their colony site, and fledged young can disperse widely, so codes like H, P, CF, FL, and FY are discouraged in most cases.
Confusing Species and Molting Adults/Fledglings: Breeding Forster’s Terns (FOTE) and Common Terns (COTE) are most often confused with each other. FOTE is the tern “with frosty wing tips”—whitish primaries compared to darker COTE primaries. Observe orange beak with black tip in FOTE compared to reddish COTE bill and black tip. Note the tail markings. COTE has a whitish tail with dark outer margin. FOTE tail appears more gray overall. It’s possible (uncommonly to rare) you might also encounter an Arctic Tern during migration; this bird is very similar in appearance to an adult COTE, except that note the Arctic Tern’s white cheeks contrast markedly with its gray throat and breast, and its shorter bill is usually blood-red to the tip. Chances are in July/August you will observe FOTE, COTE, and/or Black Tern fledged young and/or molting adults on a lake, marsh, or impoundment. Note at this time of the year marked differences in adult appearances. Fledgling and fall adult FOTEs can be readily told apart from their COTE counterparts because they have a black mask through the eye and ear, but not around nape as with the COTE. In mid-summer, molting adult Black Terns appear mottled, when the black body is largely replaced by white, and the head has a pied appearance. BLTE may be confused with molting or fledged FOTE or COTE, though the fledgling FOTE and COTE have a brownish or grayish appearance.
More information about Common Tern:
All About Birds
eBird Range Map
Birds of North America Account (subscription required)
Caspian Tern
Caspian Tern photo by Nick Anich
Profile: The state-endangered Caspian Tern is a Great Lakes obligate of open, cobble-gravel or barren, island habitats, but in Wisconsin is found only breeding at Lake Michigan sites to date. Arthur Cleveland Bent once described this bird as “the largest, the strongest, and the fiercest of all the terns.” Because of its size (19-23 in, 48-58 cm in length) and wingspan (50-55 in, 1.3-1.4 m), this black-capped species (adult) with a thick, coral-red bill—dark tip and white body, and black legs and feet, cannot be confused with our other Wisconsin tern species. If nothing else, its harsh, low-pitched calls, often heard when the bird is foraging along the Lake Michigan coastline readily identifies this tern. Adults also show more black or darker coloration on the underside of the primaries than our other tern species.
WBBA I Breeding Range – Caspian Tern
Known Colony Sites: Only 2, both off the Door County peninsula.
Arrival: 15-20 April along Lake Michigan; First 2-3 weeks of April along St. Croix and Mississippi rivers. Breeding: Nests (shallow depression in ground, sometimes lined with stones, sticks, grasses) w/2-3 Eggs: typically early to mid-June but 30 May to 4 July reported by Robbins (1991). Incubation: 26 d; Fledging: 36-56 d. Parents continue to feed young for several months after fledging.
When To Survey: First week of June (peak of incubation), but if you suspect a colony is present, don’t attempt to enter the colony. If it is a new colony not listed above, please report it to Nick Anich or Ryan Brady, and we will alert appropriate DNR staff, who will survey the site to obtain an exact number of nesting pairs.
Focal Habitat: Sparsely vegetated or barren islands, or dredge spoil sites, along Lake Michigan. Known to summer (but not breed, as far as we know), irregularly along Lake Superior at river mouths, barrier spits, and coastal islands.
Code Guidance: When near a suspected colony (indicated by a number of terns entering and leaving a site), use N for “probable nest/colony site,” C when an adult presents a fish to another adult (typically at or near the colony site), or copulation is observed, and ON for birds sitting on nests. Terns may forage or loaf on beaches miles away from their colony site, and fledged young can disperse widely, so codes like H, P, CF, FL, and FY are discouraged in most cases. Note that At this point Caspians are not known to nest away from Door County (but keep your eyes peeled).
Confusing Molting Adults/Fledglings: Fall and winter adults have orange-red bills, a black cap streaked or flecked with white, grayish primaries, and gray rectrices spotted black toward the tips. Immature birds are similar to winter adults but have brown and dusky upper parts with irregular black bars on the terminal portion of the tail.
More information about Caspian Terns:
All About Birds
eBird Range Map
Birds of North America Account (subscription required)