The Swallow Feeding Survey 2004

Patterns of foraging activity and habitat associations in Barn Swallows Hirundo rustica across the UK

In the UK, recent studies have indicated the differential regional patterns of population change for the Barn Swallow Hirundo rustica (herein “Swallow”). The causes of declines in Swallow numbers are poorly understood as this species is frequently overlooked in farmland studies, particularly in arable landscapes.

In 2004, observers were asked to count Swallows from four locations within a randomly selected 2x2 km square. These four points were over 500m apart so that the counts were independent sampling locations. Seasonal changes in the foraging pattern of Swallows were analysed from counts carried out during May and June, and then, during July or August. Coverage for the survey was excellent, involving counters from Northern Scotland, Shetland and Orkney, to Wales and southwest England (Fig. 1). The survey involved almost 800 tetrads, 3,200 sample-counts and over 15,000 Swallow records.

The strongest associations with Swallow foraging activity was the presence of livestock, especially cattle, to a lesser extent horses and then sheep, but not pigs. The presence of water was also important. Between field types, grass was preferred to crops but mainly due to the presence of livestock, and a mixture of grassland with some arable land present was associated with the highest average foraging rates. On arable land, the strongest association with Swallow activity was the presence of water and the presence of trees in boundaries. Boundaries are thought to provide shelter for insects and are especially valuable to Swallows in relatively impoverished landscapes. Generally the data show consistent selection for livestock across the UK and a tendency to prefer more complex mixed landscapes, or cereal landscapes with some trees present. The activity of Swallows varied between UK regions, being roughly higher in the pastoral north and west and lower in the arable south and east, where the declines have been most notable.

Further details are available in BTO News no 261.

Ian Henderson & Chas Holt