Adult Black Tern (photo by Gary Shackelford).
As we get closer to winter, I find myself reflecting on this past summer and a particular scene comes to mind. It is August, and we are birding with friends who are visiting from Pennsylvania. Looking out over a large bay on the south side of Lake Koshkonong we see many low-flying birds. Their wing strokes are slow, and they are swooping and dipping their bills into the water. Overall, their flight is buoyant like that of butterflies.
The birds are slim and dark with black heads, necks, and breasts. Their wings are a light gray and sometimes you can catch a glimpse of white undertail coverts. Black Terns! We count at least 70 individuals and are elated. Beginning in early August, this species is known to congregate for several weeks in good feeding areas near their nest marshes. The birds rarely plunge into the water—rather, they dip their bill into the water to catch small fish and various insect larvae. They also catch dragonflies and moths in the air, using their graceful, zigzag flight.
Focusing in on the vegetation with our binoculars, we see the characteristic begging flutter of young birds. Two juveniles standing on lily pads are being fed by their parents. As we watch, Gary’s camera catches a juvenile in flight. It has a mostly white head with a dark ear spot.
Juvenile Black Tern at Lake Koshkonong in August 2025 (photo by Gary Shackelford).
Black Terns nest across the northern part of the central and western United States into southern and central Canada. Their colonies consist of a few to over 100 birds, often near large, shallow marshes with abundant vegetation and proximity to open water. The nests are built on floating emergent vegetation such as sedges, bulrushes, and lily pads; they are sensitive to disturbance and variations in water levels. If you are kayaking or canoeing and suddenly are mobbed by small angry birds calling kyew-dik, you should immediately and carefully back off and enjoy watching them from a distance. It is best not to enter a nesting area between May 15 and July 31.
Black Tern nest with two eggs floating on a mat of vegetation (photo by Gary Shackelford).
Black Terns are in steep decline and listed as state-endangered in Wisconsin. In the Wisconsin Breeding Bird Survey of 2015–2019, nesting observations were confirmed on several locations around Lake Koshkonong, mostly during 2015–2017.
Lake Koshkonong is an impoundment of the Rock River. Water levels in the lake and the surrounding wetlands are determined by rainfall in the Rock River basin and by the operation of the Indianford dam downstream of the lake. From 2003–2021, water levels were high and fluctuated greatly. The bays and wetlands around the lake often flooded, resulting in the loss of native vegetation and increase in hybrid cattails. These conditions likely interfered with the nesting success of the Black Terns. Following major repairs to the dam in 2023 and decreased rainfall in recent years, emergent vegetation in the bays has increased and water levels in the lake and surrounding wetlands are more stable.
Adult Black Tern carrying a banded killifish (photo by Gary Shackelford).
We hope that the large number of Black Terns we saw this August is an indication of more successful nesting under these new conditions. The terns have been seen in this vicinity all summer and have also been seen foraging on the Rock River west of Fort Atkinson.
In winter, the terns migrate in a broad front through the middle of the United States. Their destinations are marine coastal areas along western Panama and the northern and northwestern coast of South America. Next spring, we hope to welcome them back to the Lake Koshkonong wetlands of southern Wisconsin.
Written by Penny Shackelford, Fair Meadows volunteer sanctuary manager
