Passage migrant and scarce summer visitor.

Swallow numbers fluctuate from year to year being affected by climatic changes, in particular cold weather whilst on migration and possible drought conditions. They are declining in Britain, this has been linked to large numbers of farms no longer having livestock and the consequent lack of insects on which Swallows feed, and also to the loss of nest sites due to farm building conversions. 

At Stevenage they were confirmed as breeding in eight of the town’s tetrads in the 1973 Breeding Atlas, in seven in the 1992 Atlas and in three in the 2012 Atlas.

Unusual nesting: in 1973 12 nested in outbuildings of Botany Bay Farm, (this farm is now part of the Great Ashby Estate), on 3 September 1977 a nest with young were seen in a Boiler House Roof at Astonbury Manor and, in 2015 and 2017 a pair nested in the underpass of the A1m at Norton Green.

The earliest spring arrival date is 14 March 1967 at Fairlands Valley. A very late autumn migrant was seen at Stevenage on 28 November 1978.

The largest recorded flocks on Spring and Autumn migration are; c.150 at Fairlands Valley Lakes on 29 April 2016 and, c.100 at Norton Green Tip on 3 August 2014.