Habitat and Ecology
Behaviour This species is a strongly migratory coastal seabird1,3. It breeds between April and June in solitary pairs or colonially in groups of up to several thousand pairs (inland colonies often smaller and more widely-dispersed than coastal ones)1. Palearctic breeders migrate south after breeding between August and October, returning to the breeding grounds in March or April1. The species may moult on arrival in its the wintering grounds (e.g. the Caribbean), during which it may become vulnerable to human exploitation9. It is gregarious throughout the year3 and shoals of fish may attract dense feeding flocks, although it otherwise feeds singly or in small loose groups1,3. In some cases, it is territorial; in Massachusetts, feeding territories usually consist of linear strips of shoreline which are occupied and defended regularly by both members of a pair. The prevalence of territoriality at feeding sites varies between colonies and is related to food species availability15. Most individuals forage 5-10 km from breeding colonies, occasionally feeding at sea 15 km offshore1. Common Terns forage over fresh water as well as marine habitats, and often follow predatory fish , waiting for panicking baitfish to surface. They sometimes forage in mixed-species flocks together with other terns26,28. Habitat Breeding The species breeds in a wide variety of habitats in coastal and inland areas from sea-level to heights of greater than 4,000 m1. Along the coast it shows a preference for nesting on flat rock surfaces on inshore islands3, open shingle and sandy beaches, dunes and spits1,3, vegetated inter-dune areas, sandy, rocky, shell-strewn or well-vegetated islands in estuaries1 and coastal lagoons3, saltmarshes2,3, mainland peninsulas3 and grassy plateaus atop coastal cliffs1. Inland it may nest in similar habitats including sand or shingle lakes shores2, shingle banks in rivers3, sandy, rocky, shell-strewn or well-vegetated islands in lakes and rivers1,3, sand- or gravel-pits2,3, marshes, ponds, grassy areas and patches of dredged soil3. Non-breeding The species winters on sheltered coastal waters4, estuaries and along large rivers, occupying harbours, jetties, piers, beaches1 and coastal wetlands including lagoons, rivers, lakes, swamps and saltworks, mangroves and saltmarshes4. During this season it roosts on unvegetated sandy beaches, shores of estuaries or lagoons, sandbars and rocky shores4. Diet The species is opportunistic, its diet consisting predominantly of small fish and occasionally planktonic crustaceans and insects1. Breeding site The nest is a shallow depression on open substrates with little or no vegetation placed near a vertical object (e.g. rock, shell, plant or artefact) to provide shelter for chicks and to facilitate nest identification1. Nest sites include the edges of bare sand amongst vegetation, rocks or logs, open areas on the margins of vegetation on beaches, the edges of mats of vegetation in marshes1, and grassy or rocky substrates on rocky islets1. The species will also readily nest on artificial rafts1. Foraging range Studies have observed foraging birds at up to 37 km from the nearest colony16,17. However, although Common Terns tend to range further than Roseate Terns17, most are observed within 10 km of a breeding colony18,19,20. At various sites, visual observations e.g. of direction of flight also suggest that most feeding trips are to sites within 10 km of the colony17,21,22,23,24, although birds in these studies were recorded at a maximum of 18 km from the colony21. Radio-tagging at the Wadden Sea has shown that birds forage at a mean radius of at least 6.3 km20, although the total distance travelled by individuals on these foraging trips is much greater, around 26-30 km. In Massachusetts, feeding territories tend to be located in shallow water up to 75 m from shore, and may be at least 8.5 km away from the breeding colony15. In terms of the preferred type of foraging habitat, studies show that flocks prefer eutrophic, shallow bays17,25, as well as areas where depth changes abruptly and tidal currents are strong, which presumably produces much upwelling and mixing of cold, deep water with warmer surface water26. Birds lower the rate at which they attempt to forage when windspeed is high27.
Systems
- Terrestrial
- Freshwater
- Marine