A new study comparing small balls of food fed by adult swifts to their offspring with trap data from the Rothamsted Insect Survey suggests that the birds could make a useful contribution to pest suppression – particularly if their numbers could be increased.

The balls of food (boluses) were analysed to work out what insects they contained and found to have a high preponderance of agriculturally important species, including pollen beetles and cabbage stem flea beetles. These specimens were compared to the numbers sampled on the same day in the nearest Rothamsted suction trap (part of the UK National Insect Survey). These beetle species are also larger than other species sampled in the area on that day.

Food boluses are small ball-like structures containing the insect prey that are regurgitated to nestlings. Boluses from adult swifts provisioning their nestlings were collected during annual ringing by birding experts at a breeding colony in Suffolk. These were taxonomically identified and compared to corresponding daily insect catches from a nearby Rothamsted Insect Survey suction trap operating within the foraging area of common swifts.