Least Terns are small, graceful shorebirds with distinctive black caps and white foreheads. They have gray backs, white undersides, yellow legs and bill, and a forked tail. Least Terns are the smallest members of the tern family found in North America.
Size and Physical Description
Least Terns are petite birds, measuring around 9 inches in length with a wingspan of 20 inches. They typically weigh between 1.5 to 2 ounces. Their slender bodies, narrow pointed wings, and forked tails give them a swift, buoyant flight style. Here is a table comparing the size dimensions of Least Terns to other common terns:
Species | Length (in) | Wingspan (in) | Weight (oz) |
---|---|---|---|
Least Tern | 9 | 20 | 1.5-2 |
Common Tern | 15 | 32 | 3.5-5 |
Forster’s Tern | 14 | 32 | 4-7 |
Caspian Tern | 21 | 50 | 14-23 |
As the table shows, Least Terns are noticeably smaller than other tern species. Their diminutive size gives them their name.
Plumage and Markings
Least Terns have distinctive black caps that extend from their white foreheads to behind their eyes and ears. Their caps are solid black on top but often have white speckles on the sides. They have pale gray backs and upper wing surfaces, with darker primary feathers. Their tails are deeply forked and grayish with white outer tail feathers.
Their undersides are white. The white extends up their necks below the black cap. Least Terns do not have a noticeable breast band like some other terns. Their slender pointed bills and short legs are yellow-orange. Their eyes are dark brown or blackish.
Male and female Least Terns have identical plumage. Juveniles have black bands on their gray wings, dusky coloration on their crowns, and some dusky barring on their undersides. The juveniles attain full adult plumage by their second year.
Seasonal Differences
Least Terns have the same plumage year-round. However, in the nonbreeding season their black caps may have variable white speckling on the sides. Their bills and legs fade to a duller yellowish in the winter months after the breeding season ends.
Behavior and Habits
Least Terns exhibit lively, energetic behavior. Their light buoyant flight, hovering ability, swift dives, and floating bobs on the water surface give them a graceful air. Here are some interesting behavioral traits and habits of Least Terns:
Flight and Foraging
- Least Terns often fly just above the water surface, with quick wingbeats and their legs dangling.
- They plunge dive from brief hovering to catch small fish near the water surface.
- Skimming low over the water, they snatch insects and dip down to pick food items.
- Their flight style is direct and tern-like, with wings held at a dihedral angle.
Vocalizations
- Least Terns have high-pitched, strident calls described as “kit-kit-kit.”
- Their alarm calls are a staccato “kik-kik-kik.”
- When disturbed at the nest, they give an urgent “arr-arr-arr.”
- Their excitement calls are quicker trilled versions of their common “kit” calls.
Interactions
- Least Terns are social and migrate and forage in flocks.
- Pairs engage in aerial displays including offering fish mid-air.
- They squabble among themselves, but aggression is usually limited.
- They may mob or attack intruders near their nesting colony.
Range and Habitat
Least Terns breed along coastal beaches, estuaries, bays, lakeshores, and river systems throughout much of the central United States. They winter in coastal areas from California through Mexico to Central America. Here are some key details about their range and habitat:
Breeding Range
Least Terns nest throughout the Great Plains states from Texas to Montana. Their breeding extends north locally to southern Canada. Along the Atlantic Coast they nest from Maine to Florida. Here is a table summarizing their main breeding areas:
Region | States / Provinces |
---|---|
Great Plains | Texas, Oklahoma, Kansas, Nebraska, Missouri, Iowa, South/North Dakota, Montana, Colorado |
Midwest | Minnesota, Wisconsin, Illinois, Indiana, Michigan, Ohio |
Southeast | Louisiana, Arkansas, Mississippi, Alabama, Georgia, Florida |
Northeast | Maine, New Hampshire, Massachussetts, New York, Connecticut, New Jersey |
West | California, Oregon, Nevada, Utah |
Wintering Range
Least Terns winter along the Pacific Coast from California south through Mexico. On the Atlantic side they winter from Florida through the Caribbean to northern South America.
Habitat
For breeding, Least Terns require open sand or gravel areas near shallow-water feeding sites. Habitats include beaches, barrier islands, sandbars, islands in rivers, lakes, estuaries, and reservoirs. They avoid areas with tall vegetation. For wintering they utilize both sandy and rocky coasts.
Diet and Feeding
Least Terns are specialized for feeding on small fish and other aquatic prey. Here are some key facts about the diet and feeding habits of Least Terns:
Prey
Small fish such as minnows, anchovies, silversides, and killifish form the main component of the Least Tern diet. They also take a wide assortment of invertebrates including shrimp, crabs, marine worms, and insects.
Feeding Style
Least Terns are visual hunters, locating prey from the air while hovering or flying low over the water. They plunge dive from flight into shallow water to catch prey. They may also pick insects and other prey from the surface while flying.
Foraging Areas
Least Terns forage near their nesting or roosting sites, typically over shallow estuaries, bays, coastal inlets, rivers, and lakes. They usually stay within a 16 mile radius of their colonies when breeding.
Feeding Range
While breeding, Least Terns on average forage within 1-3 miles of their nest site. Though they may range up to 7-10 miles from the nest to find adequate fish supplies.
Foraging Distance from Nest | Proportion of Foraging Trips |
---|---|
Less than 1 mile | 25% |
1-3 miles | 50% |
3-7 miles | 20% |
Over 7 miles | 5% |
As this table shows, around 75% of foraging occurs within 3 miles of the nest. But Least Terns are capable of longer foraging trips when needed.
Migration
Least Terns migrate long distances between their breeding and wintering grounds. Here are key facts about their migration timing, routes, distances, and behavior:
Spring Migration
- Least Terns start northward migration in late March and early April.
- They follow inland routes through the Great Plains and along coasts.
- Most arrive on breeding grounds by early May.
- Males usually arrive first and establish nesting territories.
Fall Migration
- Least Terns leave breeding grounds August – September.
- They migrate south along coasts to wintering areas.
- Most have left for winter by late September/early October.
- Juveniles and females depart before adult males.
Migration Distances
Migration distance varies by breeding location. Least Terns may migrate over 1,000 miles between nesting and winter sites. Here are example one-way migration distances from selected breeding areas:
Breeding Location | Wintering Area | One-way Distance |
---|---|---|
Southern Texas | Mexico | 500 miles |
Nebraska | Central America | 1,800 miles |
New York | Caribbean | 1,500 miles |
Utah | Mexico | 1,000 miles |
As the table shows, most Least Terns migrate at least 1,000 miles between nesting and wintering areas.
Breeding and Nesting
Least Terns nest in colonies on open sandy or gravelly areas near water. Here are key facts about their breeding habits, mating, nests, eggs, and parental care:
Breeding Season
The breeding season occurs from May through August, varying by location. Nesting typically coincides with peak fish availability in the local area.
Mating and Courtship
Least Terns mate on breeding grounds. Pair bonds may form quickly. Courtship involves aerial displays, fish exchanges, and nest scraping. Pairs are monogamous at least for a breeding season.
Nest Sites
Nests are simple scrapes or depressions in open sand or gravel substrates. Least Terns nest in colonies that provide protection from predators. Nest spacing averages around 6-15 feet.
Eggs
Clutch size is 1-3 eggs (usually 2-3). The eggs are tan or cream colored with dark brown spotting. Egg laying is spaced 1-2 days apart. Incubation lasts 20-25 days.
Chicks
Precocial chicks hatch with downy feathers and are able to move about. Parents feed chicks small fish and invertebrates. Chicks fledge in 20-25 days, but remain dependent on parents for 2-3 more weeks.
Parental Care
Both parents incubate eggs and feed chicks. Males often provide most of the fish. Females typically provide more direct brooding and defense. Parents vigorously attack intruders near nests.
Threats and Conservation
Least Tern populations declined over the last century due habitat loss and high nest failure rates. They now benefit from conservation measures at breeding sites. Their global population estimate is over 50,000 pairs.
Population Trends
Least Tern numbers dropped sharply from the late 1800s to the 1970s, but have rebounded more recently. Their current global population is estimated at greater than 50,000 breeding pairs. Here are population trends for selected regions:
Region | Breeding Population Estimate | Population Trend |
---|---|---|
Southern Great Plains | 25,000 pairs | Increasing |
Atlantic Coast | 10,000 pairs | Stable |
California | 2,000 pairs | Decreasing |
Populations remain below historical levels but have rebounded from lows in the mid 1900s before conservation measures.
Threats
Habitat loss, human disturbance, predators, and weather threaten Least Tern breeding success. Flooding commonly destroys nests. Unleashed dogs and accidents displace breeding birds. They remain endangered in several U.S. states.
Conservation
Protection efforts include fencing and patrolling nesting areas, managing water levels, controlling predators, and public education programs. These measures have significantly increased nesting productivity and allowed populations to recover from lows in previous decades.
Interesting Facts
Here are a few additional interesting facts about the Least Tern:
- Least Terns hover 10-30 feet above water and plunge dive to catch fish with dramatic splashes.
- The former name “Little Striker” referred to their aggressive defensive attacks.
- High-pitched Least Tern “kit” calls are nearly always repeated multiple times.
- Pairs preen each others’ feathers and perform elaborate reciprocal courtship displays.
- They may nest alongside related species like Piping Plovers and Snowy Plovers.
Conclusion
In summary, Least Terns are the smallest North American terns, with black caps on white foreheads and pale gray backs. Despite their diminutive size, they migrate thousands of miles and vigorously defend their nesting territories. Careful management of breeding areas has allowed Least Tern numbers to rebound from historical declines. Their graceful flight and lively nature add excitement to summers on sandy beaches, estuaries, and rivers across much of the continental interior. With continued conservation measures, these feisty little seabirds will hopefully continue to thrive for years to come.