Common Tern

Informazioni

The Common Tern (Sterna hirundo) is a medium-sized seabird, widely distributed across the Northern Hemisphere. It is known for its graceful, buoyant flight and characteristic plunge-diving feeding technique. Often found in coastal and freshwater environments, it is a migratory species, undertaking long-distance journeys between breeding and wintering grounds.

Dimensioni e longevità

Lunghezza

31-35 cm (including tail streamers)

Apertura alare

72-82 cm

Peso

90-170 g

Longevità

Up to 23 years in the wild, typically 10-15 years

Dieta

Carnivore (primarily piscivorous)

Caratteristiche fisiche

Piumaggio

Adult breeding plumage features a black cap, white underparts, and pale grey upperparts. The primary flight feathers have dark tips, forming a dark trailing edge to the wing. Non-breeding adults have a reduced black cap, often streaked with white, and a dark carpal bar on the underwing. Juveniles are mottled brown and grey on the back, with a dark carpal bar and a less defined black cap.

Forma del becco

Slender, pointed bill. In breeding adults, it is bright red with a black tip. In non-breeding adults and juveniles, it is typically black or dark red with a black tip.

Colore degli occhi

Dark brown

Colore delle zampe

Bright red in breeding adults, duller red or blackish in non-breeding adults and juveniles.

Caratteristiche distintive

Long, deeply forked tail streamers (especially in breeding plumage), slender body, buoyant flight, and characteristic plunge-diving. The red bill with a black tip in breeding adults is a key feature.

Aspetto giovanile

Juveniles have a scaly, mottled brown and grey back, a dark carpal bar on the upperwing, and a less extensive black cap that is often streaked with white. Their bill is dark, and legs are duller.

Cambiamenti stagionali

Breeding adults develop a full black cap, bright red bill with a black tip, and bright red legs. Non-breeding adults lose the full black cap, which becomes streaked with white, the bill darkens (often entirely black or dark red with a black tip), and legs become duller red or blackish. The dark carpal bar on the underwing becomes more prominent in non-breeding plumage.

Dimorfismo sessuale

Males and females are generally monomorphic in plumage, though males may be slightly larger on average. No obvious visual differences in the field.

Come identificare

1. 1

   Size and Shape

   Medium-sized tern, slender body, long pointed wings, and a deeply forked tail with long streamers, especially in breeding plumage.

2. 2

   Plumage (Breeding Adult)

   Look for the solid black cap, white underparts, pale grey back, and the bright red bill with a distinct black tip. The dark trailing edge on the primaries is also a good indicator.

3. 3

   Plumage (Non-breeding Adult/Juvenile)

   Note the streaky black and white cap, darker bill (often all black or dark red with black tip), and duller legs. Juveniles have a mottled brown back and a prominent dark carpal bar on the upperwing.

4. 4

   Bill and Leg Color

   The red bill with a black tip and red legs in breeding adults are key. Arctic Terns have an all-red bill, and Roseate Terns have a mostly black bill.

5. 5

   Flight Style

   Observe its graceful, buoyant flight, often hovering before plunge-diving for fish. This behavior is characteristic of many terns but helps distinguish them from gulls.

6. 6

   Vocalizations

   Listen for the sharp, screaming 'kee-arr' or 'kier-ick' call, which is a reliable identification cue, especially in colonies.

Habitat e areale

Biomi

Coastal areas, estuaries, large freshwater lakes, rivers, and wetlands.

Areale geografico

Breeds across temperate and subarctic regions of North America, Europe, and Asia. Winters in tropical and subtropical coastal regions of the Southern Hemisphere, including South America, Africa, and Australia.

Fascia altitudinale

Primarily found at sea level, but can be found inland along large freshwater bodies.

Ambienti preferiti

Prefers open water with nearby sandy beaches, shingle banks, rocky islets, or artificial structures (e.g., jetties, dikes) for nesting. Requires clear water for foraging.

Comportamento

Periodo di attività

Diurnal, actively foraging during daylight hours.

Abitudini alimentari

Primarily piscivorous, feeding on small fish (e.g., sand eels, herring, sprats, gobies). They hunt by hovering over the water and then plunge-diving headfirst to catch prey just below the surface. They also consume crustaceans and insects, especially in freshwater habitats.

Comportamento sociale

Highly colonial breeders, forming dense colonies that can number in the thousands. Gregarious outside the breeding season, often forming large roosts. They are vocal and territorial within their breeding colonies.

Tipo di volo

Graceful, buoyant, and agile flight with deep, elastic wingbeats. Often hovers before plunge-diving. When migrating, they fly in loose flocks with steady, direct flight.

Migrazione

Long-distance migratory species. Northern Hemisphere breeders migrate south to wintering grounds in the Southern Hemisphere, often covering thousands of kilometers. Migration occurs in large flocks, typically along coastlines.

Territorialità

Highly territorial within breeding colonies, defending a small area around their nest from conspecifics and predators. They will aggressively mob intruders.

Riproduzione

Stagione riproduttiva

Typically May to July in the Northern Hemisphere.

Abitudini di nidificazione

Nests in dense colonies on open ground, often on sandy beaches, shingle banks, rocky islets, or artificial islands. The nest is a shallow scrape in the ground, sometimes lined with sparse vegetation, shells, or pebbles.

Dimensione della covata

2-3 eggs

Descrizione dell'uovo

Typically 2-3 eggs (range 1-4), oval to pyriform in shape. Color varies from pale buff to olive-brown, heavily spotted and blotched with dark brown, black, or purplish-grey markings, often concentrated at the broader end.

Periodo di incubazione

21-26 days, incubated by both parents.

Periodo di involo

22-28 days. Young are semi-precocial, leaving the nest scrape within a few days but remaining in the vicinity and dependent on parents for food for several weeks after fledging.

Cure parentali

Both parents share incubation duties and care for the chicks, bringing them fish. Parental care continues for several weeks after fledging, with young often following adults to learn foraging techniques.

Dove trovarlo

Consigli sul campo

1. Scan for hovering birds. Look for birds hovering gracefully over the water, often pausing before executing a swift plunge-dive. This is a classic foraging behavior.
2. Listen for calls. Their distinctive 'kee-arr' call is often heard before the bird is seen, especially near breeding colonies or foraging areas.
3. Observe bill color carefully. Pay close attention to the bill color and pattern, particularly the presence or absence of a black tip on a red bill, which is crucial for distinguishing from Arctic Tern.
4. Check tail streamers. In breeding plumage, the long, deeply forked tail streamers are a good feature, though Arctic Terns also have long streamers.
5. Visit breeding colonies. During the breeding season, visiting known tern colonies (from a respectful distance) offers excellent viewing opportunities.

Specie simili

Fatti rapidi

Diet:

Small fish, crustaceans, insects

Habitat:

Coasts, estuaries, large freshwater bodies

Migration:

Long-distance migrant

Nesting:

Colonial ground nesters

Conservation Status:

Least Concern

Curiosità

• The Common Tern is one of the most widespread tern species globally, breeding across three continents.
• They are known for their impressive migratory journeys, with some individuals traveling over 10,000 km between breeding and wintering grounds.
• Common Terns are highly aggressive in defending their nests, often mobbing much larger predators, including humans, with dive-bombing attacks and loud calls.
• Their scientific name 'hirundo' means 'swallow' in Latin, referring to their graceful, swallow-like flight.
• They can live for over two decades, with the oldest recorded individual living for 33 years.

Classificazione scientifica

Regno

Animalia

Phylum

Chordata

Classe

Aves

Ordine

Charadriiformes

Famiglia

Laridae

Genere

Sterna

Specie

Sterna hirundo

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