As the bird is hunting, insects are collected in the back of the throat in a special food pouch and bound together with saliva into a ball called a bolus, which is periodically eaten or taken to the nest. These food balls can contain thousands of insects.
In rough weather, large numbers of swifts feed over water where insects are easier to catch. Swifts tend to avoid low pressure centres and other areas of bad weather. They fly into the wind in search of better weather and to get round an area of rain, and can thus fly over 800 km a day.
Swifts drink by catching raindrops in the air, or by flying low over water, skimming a mouthful from the surface.