Common Terns nest on rocky islands, barrier beaches, and saltmarshes and forage over open waters. Terns often gather over warmer waters with high densities of American sand lance (a small fish) in the spring, and tuna that help scare up smaller fish in the fall. During the winter, they gather primarily over marine habitats, foraging at sea and resting on boats and beaches.Back to top
Common Terns primarily eat small fish typically less than 7 inches long, but also take crustaceans, squid, and insects. They take fish on the wing that are close to the water's surface or plunge dive to just under the surface. They also steal fish from each other and from other tern species and gulls.Back to top
Common Terns nest in colonies on the ground in areas with loose sand, gravel, shell, or cobble pebbles typically less than 350 feet from the water. They tend to choose areas with scattered, low-growing vegetation to provide cover for chicks.
Males and females make a small scrape on the ground. Females add dead vegetation that has washed onshore, shell fragments, bones, stones, and sometimes plastic to the nest scrape before and after laying eggs.
|Clutch Size:||1-4 eggs|
|Number of Broods:||1-2 broods|
|Egg Length:||1.6-2.1 in (4.2-5.4 cm)|
|Egg Width:||1.2-1.3 in (3.1-3.4 cm)|
|Incubation Period:||22-27 days|
|Nestling Period:||20-31 days|
Olive to buff, marked with numerous dark brown spots and blotches.
|Condition at Hatching:|
Eyes open and covered in down. Hatchings are able to walk, but stay in nest.
Like other terns, Common Terns are buoyant and graceful fliers, flying with rowing wingbeats. They forage over open waters singly, in small groups, or in large flocks with hundreds of terns. They also join feeding groups of Arctic Terns, Roseate Terns, and Laughing Gulls. Common Terns are gregarious and breed in colonies. They court each other in the air and on the ground. In flight the male crouches while the female passes over him until they descend to the ground in a zigzag glide. Courting continues on the ground with the male tipping his head down and holding his wings down and out from the body while walking around the female, who points her head upward. The male starts offering food to the female, eventually feeding her almost exclusively as the pair bond is cemented. Pairs are socially monogamous, but some may seek additional copulations outside the pair, a behavior known as extra-pair copulation. Although they are social terns they aggressively defend their territories. Intruding birds are first met with a "bent posture"; adults tip their heads down and hold their wings down and out. Intruders that continue to approach are met with a more aggressive posture with the bill pointed upward and wings held down and out. When posturing fails, adults attack any intruder be it a chick or another adult, often wrestling and fencing with their bills. If humans enter the breeding colony they often dive towards them, peck their heads, and defecate on them.Back to top
Common Terns are common throughout their range and their populations were stable between 1966 and 2015, according to the North American Breeding Bird Survey. The species rates an 11 out of 20 on the Continental Concern Score, which means it is not on the Partners in Flight Watch List and is a species of low conservation concern. The North American Waterbird Conservation Plan estimates a population of 300,000 breeding birds in North America. During the eighteenth and nineteenth centuries people commonly collected tern eggs for food, which likely reduced their populations. But it was hunting for the millinery trade in the late 19th century that reduced the Common Tern population to a few thousand pairs along the Atlantic Coast. Thankfully their populations rebounded by the 1930s after the Migratory Bird Treaty Act was signed in 1918. Since then their populations have fluctuated possibly due to exposure to contaminants such as lead, DDE, and PCB; habitat degradation; climate change; and displacement by gulls. Current populations appear relatively stable, although in some areas of the U.S. the species is declining. Restoration efforts include habitat restoration, predator control, gull removal at breeding colonies, and nest site protection.Back to top
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