Celebrating the Success of the Interior Least Tern
January 12, 2021 was a day worth celebrating in the world of endangered species. On that day, the U.S. Fish and Wildlife Service formally announced that the number of interior least terns (Sternula antillarum) had met identified recovery benchmarks and that on February 12, 2021 the least tern would be stricken from the federal endangered species list.
When listed as federally endangered on May 28, 1985 less than 2,000 interior least terns remained and they were nesting in only a handful of locations. Thirty-five years of conservation management practices have resulted in the development of 480-plus breeding colonies and a 2020 population that topped 18,000 birds. From a presence in only a few states bordering the Mississippi and Ohio rivers, the least tern now exists along 2,800 miles of riverways from Colorado, Montana and New Mexico east to Indiana and south to Texas, Louisiana and Mississippi. Successful management of birds throughout 18 states, including Illinois, has led to this historic delisting.
The smallest of North America terns, the interior least tern weighs 2 ounces—the weight of a tennis ball—and is approximately 9 inches in length. Adults have a black edge to their outer wings, yellow legs and feet, and a white forehead patch. The bill of a breeding bird is yellow with a black tip while the bill is dark in non-breeding and immature birds.
This tern was documented by Meriwether Lewis and William Clark on August 5, 1804 along the Missouri River near present day Omaha, Nebraska during their “Voyage of Discovery” across North America. Numerous factors led to the tragic decline of least terns. Along with herons and egrets, the feathers of least terns became popular in the millinery industry in the late 19th century, with large numbers killed for their plumes. More recently, habitat modifications along riverways, including river channelization and construction of dams and levees, eliminated the sandbars and sandy islands where least terns nest. Humans played an additional role in the population decline as recreational activities increased on riverways.
The least tern is considered an uncommon Illinois migrant and is a rare summer resident in southern Illinois. Arriving in Illinois from late April to early June, a female tern will lay two or three pale to olive-buff eggs in a shallow depression along a sandy shoreline. Both the male and female participate in incubating the eggs for 20 to 25 days. Young will fledge at about 3 weeks of age.
Joe Kath, Illinois Department of Natural Resources Endangered Species Program Manager, had first-hand experience on the remarkable camouflage abilities of the least tern.
“At one point in an inventory of a known nest site I knelt for 20 minutes in the sand, looking in every direction for a tern nest,” he recounted. “Not until I started to get up did I notice that a chick had been next to my knee the entire time. Tern eggs and chicks blend perfectly into the substrate of sand and cobble.” For this reason, Kath describes the task of inventorying mile upon mile of riverways a daunting and labor-intensive task.
“Your best chance of locating nesting terns is to sight a pure-white adult sitting on the nest or running on the beach,” Kath explained.
Least terns feed by flying 16 to 33 feet above standing or flowing water, then dive less than 3 feet into the water to capture fish that range from 1 to 3.5 inches in length. Among the small fish least terns prey on are topminnows, shiners, stonerollers, minnows, mosquitofish, bass, shad, sunfish and carpsuckers. Fish are usually eaten on the wing, but during the nesting season they will take food to the nest for their mate and chicks. Ever the opportunist, while incubating young a least tern will nab an insect flying or crawling within reach.
Kath’s work inventorying known nesting islands also drove home how vulnerable least tern eggs and chicks are to predation.
“Nest sites are a simple scrape on the beach where no vegetative cover exists,” he said. “Coyotes can substantially reduce numbers, especially during low-water periods when river sandbars are connected to the shore. Other predators include raccoons, river otters, dogs, striped skunks, red fox, mink, barred owl, American crow, American kestrel and gulls.”
By early September, terns wing their way southward to their wintering grounds in Central America and northern South America.
In 1990 the U.S. Fish and Wildlife Service prepared a recovery plan for the interior least tern with a recovery target of 7,000 birds. Thanks to the work of conservation partners, that goal was achieved within four years. According to Kath, much of the credit goes to the U.S. Army Corps of Engineers for their work in identifying travel corridors and crucial nest sites, and for protecting birds from disturbances such as dredging and impoundments.
The decision to list or delist a species is not taken lightly but is a regimented, science-based process. At the federal level, scientists asked five questions when considering delisting the interior least tern.
- Has the range expanded?
- Has there been an increase in abundance of nesting sites?
- Are the existing populations resilient to potential future threats?
- Have best management practices been employed and will the practices continue?
- Have changes in regulatory mechanisms provided more protection for the species?
“Based on the data that had been collected on the least tern, scientists could answer all these questions with ‘yes,’ allowing for the formal decision to delist the species,” Kath explained.
Removal of the interior least tern from the federal endangered species list does not mean it comes off Illinois’ list of endangered and threatened species. According to the Illinois Endangered Species Protection Board, “endangered species” means any species of plant or animal in danger of extinction in the wild in the state of Illinois due to one or more causes including, but not limited to, the destruction, diminution or disturbance of habitat, overexploitation, predation, pollution, disease, or other natural or manmade factors affecting its prospects of survival.
“The least tern range is so restricted in Illinois that it will remain a state endangered species and we will continue to work toward state-specific recovery goals,” Kath said. “Along with a number of conservation partners, we will continue our efforts to identify suitable breeding habitat and protect the areas we can.”
It also means that if you are boating down the Mississippi or Ohio rivers on an early summer day you may find Joe Kath on his knees, intently staring into the sand and cobble, searching for well-concealed least tern nests and chicks.
Kathy Andrews Wright is retired from the Illinois Department of Natural Resources where she was editor of Outdoor Illinois magazine. She is currently the editor of Outdoor Illinois Wildlife Journal and Illinois Audubon magazine.