As I motored around the bend in the Mississippi River in my johnboat, I knew I was getting close. On the horizon, I detected a sliver of sand rising slightly above the water. I could see several terns flying over and diving headfirst into the river.
In another quarter mile, I had terns on all sides of me, and the sliver of sand was now a 30-acre island with more birds flying above it and landing on the sand. I approached the island, trimming the outboard, and the boat slid onto the shore. The terns paid little attention to me-until I stepped out of the boat and onto the dry sand.
Then the sand erupted with birds lifting off the ground and rising into the air. They protested my presence by mobbing in big circles around my head, screaming as they flew. It didn't matter to the terns that I was on the island to collect data that would shed light on their prospects for survival. I was getting the same chase-the-intruder-away treatment a coyote, a heron or an angler would receive if they were to venture onto the island.
The least terns were mobbing me because I had stepped onto one of their nesting colonies, and they were protecting their eggs and chicks. Their colonies are tight clusters of five to 100 nests on barren sand islands or sandy portions of wooded islands in the lower Mississippi River, south of Cape Girardeau. Depending upon the river level during June and July, least terns will nest upon six to 18 islands in a 210-mile stretch of the river from Cape Girardeau to the Missouri-Arkansas-Tennessee border.
Officials placed the interior least tern on the federal endangered species list in 1985. Since then the Conservation Department has been studying aspects of tern ecology. Our investigations have focused on determining how well least terns reproduce, what makes one island better than another for nesting and the birds' movements within the region.
Most recently, we looked at what places in the river held the most food for terns and how the availability of food influenced their success in raising chicks. All of this research is used by the Conservation Department to negotiate and work with the U.S. Army Corps of Engineers, which is responsible for the management of the Missouri and Mississippi rivers, to protect tern nesting habitat and encourage this species' recovery within the Midwest's system of big rivers.
The health of the endangered least tern population is tied to the environmental health of the big river basins they inhabit. As we witnessed during the floods of 1989, 1992, 1993 and 1995 in the Mississippi River valley, the ability of terns to successfully hatch eggs and raise chicks can be reduced to zero when we experience dramatic rises of the river in late June and July.
However, flooding in May can be beneficial to least terns for a couple of reasons. Spring flooding can deposit new sand on the islands and reduce chances that islands will be overtaken by young trees and other vegetation. Spring flooding also allows fish to spawn in the shallow, warmer water covering the floodplain. This results in lots of young, small fish, such as shad, minnows, carp and crappie, for least terns to eat.
Adult terns eat fish that are less than 4 inches long. Tern chicks are fed even smaller fish, and hungry chicks need to be fed about one fish every half hour. When rivers are leveed, channelized and restricted with dikes and dams, native river fish have fewer opportunities to spawn on the floodplain, which translates into fewer small fish for terns to eat.
Terns historically nested on sand islands on both the Missouri and Mississippi rivers. In his 1932 checklist of birds in Missouri, Rudolf Bennitt noted that least terns nested on the Missouri River in Lafayette County. Otto Widmann, in his 1907 book, stated that least terns were common summer residents of both rivers. Modifications that have eliminated sand islands on both the Missouri and Mississippi rivers have caused the terns' nesting range to dwindle. They now nest only in the southeastern tip of the state. Since 1985, researchers have found tern colonies only in or adjacent to Scott, Mississippi, New Madrid and Pemiscot counties.
Terns are expert colonizers when they can find suitable new habitat. Several terns that Missouri researchers banded between 1987 and 1991 have nested at a new colony next to a cooling pond in Indiana-190 miles from their original home! A few of our banded birds also showed up on the Upper Missouri River in South Dakota. Similarly, Missouri sites attract birds from other nesting areas that are undergoing flooding or other habitat disruption.
Today the number of least terns in Missouri ranges between 500 and 900 nesting pairs. We are concerned, however, that these sand island nesters are not reproducing at a rate to maintain these numbers. We will continue to monitor them and protect them, but our research confirms they can survive only if they have suitable big river sand island habitat. Without suitable nesting habitat, we will have no least terns. And without new or restored habitat, their numbers will not grow.
Before leaving, I post signs around the island requesting people not to disturb the area during the tern breeding season, which runs from late May through August. As I drift away in the boat, the terns settle back onto their nests and resume feeding their chicks. It's a reassuring sight and seems to indicate a successful nesting season. We need that-and many more-if least terns are going to continue to inhabit Missouri's sand islands.
by Amy Salveter
Drawing its waters from a half million square miles, the Missouri River is the lifeblood of the central U.S. At one time, the "Big Muddy" sprawled across vast prairies, pulsating beyond its banks 300 feet during a single rise, shifting and depositing huge loads of nutrient-rich silt across the floodplain, sometimes relocating itself by a half mile in one year. These natural fluctuations created a rich variety of shallow- and deep-water breeding and feeding grounds-a complex web of life-that supported unique plants, fish, migrating birds and other animals.
Our efforts in this century to tame the unpredictable river have transformed the Missouri into a highly engineered, constrained system. Animals like the sicklefin and sturgeon chub-tiny fish near the beginning of the river's food chain-are suffering from dramatic modifications to the river.
The Big Muddy isn't as muddy as it used to be. Dams and rock-lined banks have reduced sediment in the river, lifting the muddy shroud that once helped hide the chubs from predators. The construction of 1,400 miles of levees has eliminated shallow, slow-moving side channels the fish need to feed, hide and reproduce.
The chubs' main food source-aquatic insects living among woody debris and vegetation-has become scarce. Because the river has been severed from its floodplain, sufficient trees and leaves no longer routinely wash into the river, and the destruction of side channels and islands has eliminated places where debris collects. Due to the channelization that supports barge traffic, today's Missouri flows twice as fast as the river Lewis and Clark knew, forcing the chubs to use more energy just to stay in one place.
The Missouri has been deemed one of the nation's "most endangered" rivers by American Rivers, a leading national river conservation organization. The group ranks rivers throughout the U.S. that are threatened by development, dams, pollution and other problems. The sicklefin and sturgeon chub are not the only fish species suffering from the impacts of habitat degradation. Pallid sturgeon, paddlefish, sauger, blue sucker, flathead catfish, longnose gar, blue catfish, flathead chub, speckled chub and silver chub are other species struggling to survive in the radically altered-and endangered-Missouri River.
To learn more, write American Rivers, 1025 Vermont Ave. NW, Suite 720, Washington D.C., 20005; or visit their website.
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