Migrations and winter quarters of five common terns tracked using geolocators

Ten geolocators (light-level data loggers) were attached to Common Terns (Sterna hirundo) at a breeding site in the northeastern USA in 2007 and 2008; six were retrieved (five with useful data) in 2008 and 2009. The birds wintered in four discrete areas on the north and east coasts of South America, from Guyana (6–7°N) to northeastern Argentina (36–42°S); three remained within restricted areas for most or all of the winter, whereas two ranged more widely. They left the breeding area at various dates between 1 August and 14 September; three migrated directly from the breeding area while two first moved southwest to stage near Cape Hatteras. All five birds flew directly to the vicinity of Puerto Rico, then moved along the north and east coasts of South America, staging at scattered locations for periods of 3–11 d, before reaching their winter quarters at various dates from 6 September to 26 October. Two birds left their winter quarters on 2 March and 4 April, staged in northern Brazil for 47 and 6 d, then traveled via the Bahamas to reach the breeding site on 1 May. During breeding and post-breeding periods, the birds spent a mean of 7 min each day and virtually no time at night resting on the water, but during the rest of the year they often rested on the water for up to 6 h by day and up to 11 h at night. Leg-mounted geolocators caused several adverse effects but did not reduce survival.

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