By Kate Crowley
Most people don’t see terns very often unless they spend a lot of time on or around large bodies of water. Terns are considered seabirds, but each spring a number of species migrate to Minnesota. The four that are most commonly seen are the Caspian, Common, Forster’s and Black. The first three all share certain features; grey wings, white breast, black on the head, forked tails and long, bright orange bills. At times it can be difficult to differentiate a Common from a Forster’s, but there is no way to misidentify a black tern. As the name implies they have black bodies and heads, with silvery grey wings and a short notched tail.
We have been fortunate this summer to see lots of black terns on the Mississippi River, beginning in late May when we paddled our canoe through the vast wetlands just south of the headwaters. At that time the graceful flyers were busy swooping and calling as they set up their courtship and nesting territories. Three to four eggs will be laid in nests built in emerging vegetation and sometimes on floating mats of vegetation, almost in the water. Amazingly, studies have shown that the eggs themselves are able to be in these very wet conditions and not reduce the probability that they will hatch. But the eggs and young remain vulnerable to boat wakes, wind driven waves and heavy rainstorms.
In July we took our small fishing boat and motored up to the wetlands above the Brainerd flowage and once again saw the birds swooping over more wetland vegetation growing in the middle of the river. They would have had their young by this time, but after leaving the nest at 2-3 days after hatching, the young hang out in the thick vegetation, well hidden from predators. Finally, we saw them again just last week as we motored into Lake Irving which is one of the first of a series of lakes from Bemidji going south to Lake Winnibigoshish.
As we came under a series of bridges we saw a number of buoys – one red and one green, as well as several white ones warning ‘no wake’. Sitting on top of each buoy was a tern. From a distance we couldn’t tell what species they were, but flying all around and calling were more black terns. We saw one or two swoop down to the bird on the buoy and transfer something from one beak to the other. As we got closer we could see that these were immature black terns, a mottled mix of white, grey and black and though they could fly, they were still being fed by their parents. Also sitting on one of the buoys was a Forster’s tern which is commonly found in the same areas as black terns.
Most terns catch their food by diving into the water, but black terns eat both insects and fish and will hunt the air much like nighthawks, moving in zigzag pursuit of their prey. They skim rather than dive into the water to catch small fish. While raising their newly hatched young, most of the food is insects, which are abundant around the marshy vegetation they prefer. Once the young have learned to fly, at about three weeks, they and their parents move to more open water sites.
So, though we never actually saw the nests and newly hatched chicks of these birds, we had actually seen them throughout their summer breeding season in Minnesota and now, as August draws to a close, the young are preparing, along with their parents for the journey south. Black terns switch habitat in the winter months and become residents of tropical coastal areas, mainly off South America.
Like too many other species of birds black tern numbers have shown a marked decrease since the 1960s. There are many reasons, but the most significant is probably loss of habitat. These are birds that absolutely depend on healthy and large wetland of 50 acres or more. The vegetation needs to be a mix of sedges, reeds, rushes, pond lilies, water lilies, broad-leaf arrowhead, sweet flag and wild rice to name just a few.
I was under the impression that everyone was acutely aware of the importance of wetlands to the overall health of our state, wildlife and water systems, so I was shocked to read in the Star Tribune on July 31st that Minnesota has lost 312 square miles of wetland and the accompanying vegetation in five years. The DNR posted a report that indicated overall wetlands had increased by 2000 acres from 2006 to 2011, but these were “largely ponds or wet areas on farm fields that are farmed during dry periods.” These are not true wetlands, the kind that have existed and evolved over the centuries and that our migratory birds depend upon for continued survival. Black terns use different wetlands or different parts within wetlands from year to year, so a large and complex system is critical. A vast cattail marsh will not cut it for these birds.
One of the places not too far away where you can go to see black terns is the Sand Prairie Wildlife Management & Environmental Education Area on the southeastern edge of St. Cloud. Long ago, this was once a channel of the Mississippi River. In more recent years, native prairie plants recolonized what were abandoned farm fields. There are two major wetland restorations. South of County Road 7, signs mark the entrance on the east side of U.S. Highway 10. An easy three-quarter mile walk to the observation deck will give you a chance to look for the terns, as well as other wetland birds. Do it soon, because the solar clock is ticking and the birds will soon follow that great star as it moves away from us.