Dateline – July 2023 – Denton County

Terns are a family of seabirds birds characterized by their similarity in appearance and behavior. What variations there are between tern species generally manifests in size, coloration, and conduct. Of all the terns found in North America, the Least Tern is the smallest–roughly the same size as a Northern Mockingbird, with Least Terns possessing longer wings and heavier bills than the State Bird of Texas.

Least Terns are sleek birds designed for speed, as evidenced by their long pointed wings and streamlined silhouettes. Adult Least Terns wearing their breeding plumage are largely white underneath, with gray feathers covering their upper surfaces. Their heads sport a black cap and mask. Bills are bright yellow, while their feet are colored a darker shade of orange. Non-breeding adults have a more subdued plumage and a darkly colored bill. Juveniles forego the gray feathers of the adults in favor of a faintly barred pattern on their top-sides.

An Interior Least Tern over Denton County

Least Terns feed almost exclusively on small fish that they pluck from sizeable, but shallow, bodies of water. When hunting, Least Terns cruise at low altitude, flying just above lakes and ponds in search of prey. On occasion, they will hover in place until they draw a bead on their intended victim. Once a likely target is spotted, the Least Tern will wing over in a steep dive and hit the water hard in an effort to snag the hapless minnow swimming just below the water’s surface.

Hovering above the water, looking for an unsuspecting minnow!
Winging over to begin its dive!
A steep dive is required to catch the minnow unawares
A sequence of photographs illustrating the Least Terns hunting technique
Plucking a hapless minnow from the water!
This bird is headed back to the nest with food for its hungry babies!
Not every attempt is successful

There are a several subspecies of Least Tern in North America. Each inhabits and breeds in a unique range on the continent. The Interior Least Tern (Sterna antillarum athalassos) is the subspecies found in North Texas. These birds are so named because they breed in the interior of the continent–mostly along the Mississippi River valley and some of its western tributaries.

Texas Parks and Wildlife : Interior Least Tern (Sterna antillarum athalassos)

In North Texas, Interior Least Terns historically were found nesting on sand and gravel bars near the Red River. For years, Least Terns–of all subspecies–have been declining in number as much of their preferred habitat has been repurposed or otherwise taken over for human use. The Interior Least Tern was no exception–the subspecies found here in North Texas was also in trouble.

Only a few decades ago Least Terns were seldom seen in Dallas/Fort Worth area, even though the metroplex is located only a short distance from their breeding grounds on the Red River. But, in our part of North Texas the situation has recently changed for the better. Interior Least Terns are now relatively common all across Dallas/Fort Worth. Something important changed in the intervening years!

The historic range of Least Terns was along the coast and a swath following the Red River valley
Now Least Terns can be found all over the state!
There is a healthy and growing population of these birds in the Dallas/Fort Worth area

Least Terns breed in the summer. They begin their courtship in late spring, and spend up to five month at their chosen site incubating eggs and raising their young. Least Terns often nest in large colonies, preferring large flat sand bars or gravel bars as places to construct their nests. Abundant habitats like these are what historically inspired terns to form nesting colonies along the Red River in North Texas

Least Tern nest on sandy beaches near the ocean and on gravel bars found along rivers.
Picture courtesy Wikimedia Commons
Sand and gravel bars along the Red River were the bird’s favorite nesting sites in North Texas. Picture courtesy Wikimedia Commons
Feeding its offspring a small fish.
Picture courtesy Wikimedia Commons
Keeping baby terns well fed is a never-ending task!
Picture courtesy Wikimedia Commons

Over the last several decades there has been a boom in warehouse construction in DFW. These large buildings are often built in locations close to the Trinity River, its tributaries, or its many borrow-pit lakes. Even more, these warehouse have large flat roofs which are sometimes covered with gravel. As it turns out, these roofs can be excellent stand-ins for the sand and gravel bars Least Terns prefer to nest on. Today in North Texas, these adaptable small birds are making ready use of these man-made nesting grounds.

The result is an incredible rebound in Interior Least Tern numbers all around the metroplex and in other places across their range in Texas. In 2021 their population had recovered to the point where the Interior Least tern could be removed from the endangered species list. While only a few decades ago seeing a Least Tern in Dallas/Fort Worth was rare sight–usually a migratory bird–today there is a healthy and growing population to be found living right here in the metroplex. Least Terns can be readily observed in many places around town.

The “interior” Least Tern, which nests in the vast Mississippi River drainage, was listed as Endangered in 1985 when the population was estimated at fewer than 2,000 birds. By 2021, following years of conservation efforts, the population had increased to 18,000, allowing the species to be removed from the Endangered Species List.

The Cornell Lab All About Birds
Ware house and business parks like this one are going up all over the Dallas/Fort Worth metroplex!
These buildings typically have large flat roofs covered with gravel or similar material
Roofs like these can be good analogs for natural gravel bars
In Dallas/Fort Worth it is very common for warehouses to be constructed
in areas close to rivers and other water features
When the buildings are located near water, they can be excellent nesting sites for terns

With steadily increasing numbers across North Texas, there are now many places around Dallas/Fort Worth where Least Terns can be observed. When Least Terns are found hunting for minnows and other small fish, they can be quite enjoyable to watch. Often the birds will make multiple passes over a body of water in their search for suitable prey–creating ample opportunities for observation and photographs. Even more, when the terns fly into a steady headwind, it slows their normally erratic flight, and can hold them virtually stationary midair as they hover hunt. This is an especially nice accommodation for wildlife photographers attempting to capture images of these normally very speedy birds.

In Dallas/Fort Worth Least Tern numbers are increasing
There are many places around town where they can be observed

If you discover a place where Least Terns are fishing, it is possible to spend hours watching their aerobatics. In some situations they can be observed at very close range. We’ll close out this article with a selection of photographs of Interior Least Terns in action, photographed right here in the Dallas/Fort Worth metroplex…

This sleek bird is an agile flyer
Snatching a minnow from the water!
On the lookout for an unsuspecting minnow!
Least Terns are strong flyers
Coming off the water with a fresh catch!
Sometimes these birds will call out while on patrol
Zipping past a powerline
A sharp-eyed bird!
Least Terns will sometime hover momentarily
before committing to a dive
Fighting a strong headwind, this bird was held nearly stationary in midair
Those sleek wings resemble the blades of a sickle!
Winging over into a dive!
Searching for prey
Hurrying back to the nest!
Preparing to dive!
Another great catch!
Hunting through the last light of day

2 Replies to “Interior Least Terns: Their Numbers are on the Rise!”

  1. Really nice article, Chris, with good photography. BTW, the fish the bird early in the article was carrying is an inland silverside, Menidia berylina, fwiw.

    1. Oh, and a later photo, captioned “Back to the Nest,” shows a bird with what is probably a threadfin shad, _Dorosoma petenense_.

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