The Least Tern (Sternula antillarum) is the smallest member of the tern family Sternidae. Terns are seabirds closely related to gulls, but they are usually lighter and more slender with long pointed wings and forked tails. The Least Tern is the smallest tern species in the world, reaching only about 24-29 cm in length and weighing just 33-48 grams.
This tiny tern breeds on beaches and coastlines across North America, and migrates to coastal areas of Central and South America during the non-breeding season. The Least Tern is known for its aerial agility and its sharp, piercing calls. Its diet consists primarily of small fish and invertebrates, which it catches by diving from the air into shallow water.
Here are some quick facts about the Least Tern:
- Scientific Name: Sternula antillarum
- Length: 9.5 – 11.5 inches (24 – 29 cm)
- Wingspan: 20 – 24 inches (50 – 60 cm)
- Weight: 1 – 1.5 ounces (33 – 48 grams)
- Population: Approximately 183,000
- Conservation Status: Least Concern
In this article, we’ll go into more detail about the identification, behavior, breeding, habitat, diet, and conservation status of the Least Tern. We’ll also look at some interesting facts and frequently asked questions about this tiny seabird.
Identification
The Least Tern is the smallest tern species in the world. Adults have pale gray upperparts, white undersides, a black cap on the head, and a white forehead. The legs and bill are yellow with a black tip on the bill. They have pointed wings and a deeply forked tail.
In breeding plumage, the Least Tern has a black stripe that runs from the eye to the base of the bill, and a small white triangle on the forehead. Non-breeding adults have a darker gray back and a diffuse black cap. Juveniles are similar to winter adults but with dark bars on the wings and tail.
The Least Tern’s size, black cap, yellow bill, and swift flight on rapidly beating wings help distinguish it from other small terns and gulls. It is often seen hovering above water before diving to catch small fish. Its high-pitched ‘kip kip kip’ call is commonly heard at nesting colonies.
Behavior
Least Terns are highly aerial and agile fliers. They feed mostly on small fish and invertebrates like shrimp, which they catch by plunge diving from heights of 6 to 20 feet. They also pick prey items from the water’s surface while flying.
These birds are migratory, wintering along the Central American coast and the northern coast of South America. They migrate in flocks, sometimes joining other tern species.
Least Terns are gregarious and nest in colonies of up to 100 pairs, often with other tern species. Courtship involves aerial displays and fish transfers between mates. They are monogamous and pairs may stay together over several breeding seasons.
Both parents share incubation and caring for the young. Least Tern chicks hatch after about 21 days and are fed fish and invertebrates by the parents. Chicks fledge in 17-25 days but remain dependent on the parents for another few weeks.
Breeding
The Least Tern breeds in scattered coastal colonies across much of North America. The breeding range extends along the Atlantic Coast from Maine to Florida, and along the Gulf Coast to Mexico. There are also breeding populations on the Pacific Coast, inland at lakes and rivers, and locally in the Caribbean and northern South America.
These birds arrive at breeding sites from late April to June. They nest on open sandy beaches, tidal flats, dunes, and salt pans along the coast. Inland populations may nest on sandbars in rivers, gravel pits, or reservoir shores.
Nests consist of a simple scrape in the sand with little or no lining. Least Tern colonies can number from 10 to 100 nesting pairs, sometimes mixing with other tern species.
The female typically lays 2-3 speckled, tan-colored eggs. Both parents incubate the eggs for about 21 days before hatching. The precocial chicks are able to move around soon after hatching. They fledge in 17-21 days and remain dependent on the parents for 3-4 weeks after fledging.
In some regions, Least Terns may raise two broods per season. They show strong nest-site fidelity, often returning to the same breeding colony year after year.
Habitat
The Least Tern inhabits coastal beaches, barrier islands, tidal flats, inlets, shoals, and sandbars along the Atlantic, Gulf, and Pacific coasts. Its nesting habitat consists of open sandy or gravelly areas near shallow-water feeding sites.
Inland populations use river systems. They nest on sandbars, islands, and lake and reservoir shores. Wherever they nest, proximity to clear, shallow water for foraging is key.
During the non-breeding season, Least Terns use similar coastal habitats further south – estuaries, bays, harbors, river mouths, and lagoons from Mexico to Peru. Mangrove swamps and salt pans are also important wintering habitats.
Suitable Least Tern habitat has minimal vegetation, providing open visibility and enough camouflage for nests. Predator-free habitat is also critical for nesting success. Human disturbance can make habitats unsuitable for breeding.
Diet
The Least Tern is a fish-eating species, feeding primarily on small shallow-water fish. Common prey includes species like silversides, topminnows, killifishes, anchovies, menhaden, and minnows. The size of fish prey is typically between 1-6 inches long.
Invertebrates like shrimp and other crustaceans are also important foods, especially during the breeding season. Least Terns may occasionally eat large insects as well.
Foraging occurs mostly by shallow plunge-diving from brief hovering flight. Least Terns also pick prey from the water’s surface while flying along. They usually forage in shallow estuaries, bays, inland lakes, and rivers.
Feeding ranges are limited during breeding, with most foraging occurring within a couple miles of the nesting colony. Maximum foraging distances are around 12 miles from the nest. More extensive feeding ranges are used during migration and winter.
Conservation Status
The Least Tern has a large range and a global population estimated at over 183,000 individuals. The overall population appears to be stable, so the species is evaluated as Least Concern on the IUCN Red List.
However, some local and regional populations have declined or been extirpated. Least Tern numbers in several U.S. states qualify the species as threatened, endangered or a species of special concern.
Major threats include human disturbance, habitat loss, and predation. Coastal development, dams, water diversion, and vegetation encroachment all degrade nesting habitats. Introduced predators, off-leash dogs, vehicle traffic, and human recreation all disturb colonies.
Conservation measures like habitat protection, public education, predator control, and managing water levels have aided many Least Tern populations. Ongoing monitoring and protection are needed to maintain populations of this diminutive tern.
Interesting Facts
Here are a few interesting and unique facts about the Least Tern:
- The Least Tern is the smallest member of the tern family Sternidae worldwide.
- Its breeding range only overlaps with the very northern part of the Arctic Tern’s massive breeding range.
- Least Terns are one of the only two tern species found regularly inland in North America.
- They have a faster wingbeat compared to similar-sized terns.
- Nests are situated above the high tide line to avoid flooding.
- Pairs may engage in elaborate aerial courtship displays.
- They are vulnerable to disturbance while nesting, often leading to exposure of eggs and chicks.
- Parents shade eggs and chicks from the sun by standing over them with outstretched wings.
- Least Tern chicks can swim short distances if forced to leave the nest.
Frequently Asked Questions
Here are answers to some common questions about the Least Tern:
Where do Least Terns live?
Least Terns are found along the Atlantic, Gulf and Pacific coasts of North America during the breeding season. They migrate down the coasts of Mexico and Central America in winter.
What do Least Terns eat?
Their diet consists mostly of small fish like silversides, anchovies, and minnows. They also eat some invertebrates like shrimp.
How do Least Terns catch fish?
They plunge dive from brief hovering flight to catch fish near the water’s surface in estuaries and shallow coastal waters.
Do Least Terns swim?
No, Least Terns do not swim. The adults are aerial and use their wings for diving to catch prey. Chicks can swim short distances if displaced from the nest.
How many eggs does a Least Tern lay?
Typical clutch size is 2-3 eggs. The eggs are speckled tan, brown, or olive.
Are Least Terns endangered?
Some regional populations are endangered, but the overall Least Tern population is still considered Least Concern globally.
Why are Least Terns threatened?
Habitat loss, human disturbance, predation, and changes in food supply threaten Least Tern populations. Their limited breeding habitat makes them vulnerable.
How can we help Least Terns?
Protecting breeding sites, managing water flows where they nest, controlling predators, and limiting human recreation near colonies helps conserve Least Terns.
Conclusion
In summary, the Least Tern is the smallest member of the tern family worldwide. It breeds on sandy beaches and river bars across coastal North America and winters along the coasts of Mexico and Central America.
This agile hunter feeds mostly on small fish and nests in colonies that are highly vulnerable to disturbance. While still relatively common overall, degradation of breeding habitat has put some populations at risk. Protecting nesting sites and limiting human activity is crucial for continued survival of the Least Tern.
Despite its tiny size, the Least Tern is well adapted to its coastal and inland riverine habitats. It fills an important ecological niche as a predator of small fish and invertebrates. Conserving the Least Tern helps preserve wetland and beach ecosystems and balance aquatic food webs. With appropriate habitat protections, this diminutive tern will hopefully continue its aerial acrobatics and lively calls along coasts for years to come.