Black terns are irregular passage migrants at Paxton Pits, usually seen in spring, as birds moving from their wintering grounds in Africa overshoot their breeding marshes, the nearest of which are in the Netherlands (though pairs have bred in Cambridgeshire, in 1966, 1969 and 1975).

Almost all the records are during a four-week period from 20th April, with the first week of May providing the main passage.  Most fly straight through, feeding on flying and surface invertebrates as they go, though occasionally birds stop, and occasionally roost.