Least Tern

The Least Tern is a sociable birds that resides in colonies along coasts and riverbanks of the American continent and the Caribbean islands. One can easily spot them along sparsely vegetated beaches and islands that are free from tidal or river action.

About Least Terns

They are the smallest of the American Terns and thus are not very strong. They may reside in colonies to shield themselves from external threats, as there is strength in numbers. Nevertheless, they are capable of flying in majestic and acrobatic aerial patterns that make them a sight to behold.

Recently, these humble birds have managed to adapt their nesting habitats to challenging circumstances. Due to the increase in human activity along coastal shorelines and riverbanks, viable habitats have shrunk drastically. As a result, the innovative Least Terns nest on flat gravel rooftops, adapting the nest to suit the new surroundings.

An intriguing feature of these birds is that they are capable of flying long distances. Male birds habitually fly up to 6 kilometers away from the nesting site to find food, which is impressive for a bird of its size.

Furthermore, it is one of the few birds that depicts an uncommon molting pattern. The primary feathers are replaced in a sequential process during the molt, which means that the bird can have up to 3 generations of feathers on its body. Least Terns seem particularly interesting, don’t they? Let’s learn a little more about them.

● Least Terns Photos, Color Pattern, Song
● Least Terns Size, Eating behavior, Habitat
● Least Terns Range and Migration, Nesting

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Least Tern Color Pattern

The Least Terns acquire the basic and alternate plumage through complex and unusual molt patterns. The primary feathers are replaced from innermost to outermost.

Hatchlings have no well-defined feathers and are nearly white or tan in color. Small feathers can be observed in the following three weeks. The juvenile plumage consists of a brown buffy wash on the back, wings, and head. Whitish feather edgings give the back and the wings a scaly appearance. The black crown and eyestripe are visible, along with a dark bar on the edge of the wing.

The basic plumage replaces the brown feathers for grey ones and the buffy regions of the head become increasingly white. The wings begin to appear less scaly and the back is less pronounced. The bill and legs are darkly colored.

The alternate or breeding plumage is similar to the basic plumage, with the exception that the bill is yellow and the legs are orange-red. The striking black crown pattern is an eyecatching aspect of this bird.

Description and Identification

Least Terns are the smallest of all North American Terns. They have narrow, pointed, greyish wings that make it easy to swoop through the air and catch prey. One can easily spot them due to their distinctive black cap and white body in coastal regions.

The thin yellow bill and scaley yellow legs visible during the breeding season help distinguish the birds from similar species such as the Peruvian Tern.

There is no physical disparity between the sexes as they both have similar plumages. It is much more reliable to distinguish the two sexes by their behavior.

Least Tern Song

Although Least Terns can not produce songs, they are still very noisy. Basic vocalizations are very similar to the Little Terns’ vocalizations. Although some Least Tern calls are less sharp and deeper, than corresponding calls of the Little Tern, several other types of calls are identical.

Juveniles produce cheap calls to plead for food. The calls are high-pitched and consist of 2-3 distinct parts, which distinguish them from adult calls. It sounds like “twee-dididi-twi”. Adult Least Tern calls are used to recognize and contact their young or other females, they are high-pitched, sharp sounds. These calls sound like “kee-zink” or “kip-kip-kip-kiddeek” and can sometimes be heard 1 kilometer away.

The birds generate alarm calls to alert the colony to a potential threat. During times of severe danger, the birds elicit sounds like “zwreep” mixed with high-pitched “tsip tsip tsip” or a staccato “kit-kit-kit-kit”.

Least Tern Size

Least Terns are the smallest of the North American Terns. Adults, on average, span 8.3 to 9.1 inches from head to tail and weigh between 36 to 54 grams. There isn’t any sexual dimorphism between the sexes. Adult males and females are of similar sizes.

The average wingspan ranges between 18.9 to 20.9 inches. They have bilaterally symmetrical and endothermic bodies. There are no geographical differences.

Least Tern Behavior

Least Terns are active birds. They take strong, direct flights. They perform a wide variety of acrobatic maneuvres when foraging or responding to disturbances in colonies. Their flight patterns are strong and graceful; however, these birds are light enough to be blown away by strong gusts of wind.

The birds are diurnal and roost at night. During the breeding season, adults stay in the colony at night unless they face external threats. Least Terns can be territorial in the vicinity of potential nest sites.

The males often defend their sites while soliciting mates or establishing pair bonds, against other males in the region. Territorial defenses consist of alarm calls and attack flights; often these alarm calls alert other birds in the colony who swoop in to defend the colony against the intruder.

Like most bird species, Least Terns are monogamous but typically do not mate for life. Many Least Terns only pair for a single breeding season. It is unknown if the pair bond continues during the migration period.

Least Terns’ courtship ritual is fascinating as it has two phases. The first phase is the aerial phase that includes fish flights and aerial glides. The male will fly in specific patterns with a fish in its bill to entice females. The second phase is the ground phase which includes courtship feeding, posturing, parading, and copulation.

What do Least Terns Eat?

The birds primarily forage in coastal waters. They primarily feed on small fishes, shrimp, crustaceans, and other water-based invertebrates. Terns swoop in to catch fish and aquatic invertebrates in the upper 15 cm of the water. They appear to select shallow-bodied fish.

Terns usually forage throughout the day. They scan shallow waters while hovering up to 10 meters above and quickly plunge from great heights to capture prey with open mandibles. After the capture, they quickly rise well above the water level to manipulate and swallow the food in flight. Sometimes they may also capture insects that skirt across the surface of the water.

An interesting feature is that incubating birds normally do not leave the nest during this process and tend to feast on insects that hover near their heads.

Least Tern Habitat

Notably, Least Terns are sociable birds who form colonies on bare or sparsely vegetated sand or dried mudflats along coasts or rivers. They may also construct colonies on sandy islands, gravel, and sandpits.

The birds primarily use materials like sand and seashells as they are widely available. Their nests are usually built with materials that they dredge up from the nearest water bodies. Even though colony sites can sometimes be unstable, the birds display loyalty to specific sites. One potential reason for this behavior is that suitable sites are limited due an increase in human activity.

Nesting habitats have changed since the start of the twentieth century, especially in places such as the Gulf of Mexico and California. Beach habitats are transforming into places for human recreation and residential developments. This has led to water diversion and changes in the level of vegetation which has reduced the amount of habitable land.

Many Least Terns have thus turned to alternatives such as agricultural fields, parking lots, and graveled rooftops. However, these new habitats can be inefficient due to external factors such as excessive heat and domestic pets.

Little is known of the Least Terns’ winter habitats. Some evidence suggests that the birds settle in coastal lagoons and mudflats in Columbia.

Range and Migration

Least Terns are native to the American continent and the Caribbean islands. During breeding months the birds inhabit the coastal regions of the United States, Mexico, and the Caribean Islands. They have a very wide foraging range; during the breeding season, they can travel up to 6 km away from the nest site to find food.

Post the breeding season, the birds tend to fly southwards towards Central and South America. It is interesting to note that American Terns usually fly the longest distances to reach South America.

Least Terns migrate in small, loose groups and feed en route in shallow waters near land and take regular breaks on beaches and docks during their journey. However, migration dates may vary as adults with fledged young can linger in breeding regions for 6-8 weeks before departing.

Least Tern Lifecycle

Least Tern clutch sizes range from 1-3 eggs per brood, with only one brood per season. Scattered instances of two broods have been observed, but they are incredibly rare. The egg incubation period can last anywhere between 19 to 25 days whereas the nesting period only lasts 1-2 days. The eggs appear pale green with spots of grey, brown, and black. Both males and females incubate the young.

The chicks remain fledglings for 2-3 weeks, post which they start flying. However, they do not fly independently for up to 3 months after hatching. The birds fully mature 2-3 years after hatching and engage in reproductive activity.

The typical lifespan for Least Terns is between 15 and 20 years. However, the longest lifespan recorded in the wild is a whopping 27 years for a New Jersey Least Tern!

Nesting

The nests are built from materials such as pebbles, sand, or soil. Both male and female birds build their nests by scraping shallow holes in the materials and then line their nest with debris.

The birds make these scrapes by sitting on the materials and kicking their feet backward while rotating their bodies. Additionally, they use their breast to form shallow depressions. Small bits of wood or grass may be added after incubation has begun.

Nests, on average, are 2 centimeters deep and have a diameter of 7-10 centimeters. Given that the nests are relatively easy to construct, renesting birds rarely use the same nest in the future.

Anatomy of a Least Tern

These birds are easily identified through their striking well defined black eye-stripe, dark bar on the edge of the wing, and dark gray inner primaries. During the breeding season, the bill is yellow with a variable amount of black at the tip. During off-breeding seasons, the bill is much darker and can appear blackish or dull orange.

Least Terns have small, plump, white-greyish bodies. The underparts of the birds are grey and white while the two outermost primaries are black. The wings can be 15 to 18 centimeters long and consist of white and grey feathers.

The legs, like the bill, change color depending on the season. During breeding seasons, the legs appear red-orange, while during non-breeding seasons, the legs appear black.

Final Thoughts

Least Terns are one the most innovative birds in the world considering their quick response to their depleting habitat. The effort that they put in to protect their family and colony by relocating their nests and working together is truly extraordinary.

Watching these brilliant birds in flight, performing majestic aerial acrobatic maneuvers is remarkable. They are capable of plunging from heights of up to 10 meters to capture fish at the water surface within seconds!

It is unfortunate that despite their best efforts, the Least Tern population has declined by 88% between 1966 and 2015. The primary factor that has contributed to this decline is that their main habitat is heavily coveted by humans. The species has officially been classified as a threatened or endangered species.

Ornithology

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Bird Watching Binoculars for Identifying Least Terns

The most common types of bird watching binoculars for viewing Least Terns are 8×21 binoculars and 10×42 binoculars. Bird Watching Academy & Camp sells really nice 8×21 binoculars and 10×42 binoculars. You can view and purchase them here.

Least Tern Stickers

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Bird Feeders For Least Terns

There are many types of bird feeders. Here are our favorite bird feeders for your backyard. We use all of these bird feeders currently. Kids will have a great time watching birds eat at these bird feeders. Using this collection of bird feeders will provide a wide variety and many types of birds.

Best Bird Houses For Least Terns

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