Insect-eating strategies
Most land birds consume insects at some stage in their life cycles, many only when they are youngsters, fed protein-rich packages of caterpillars, eggs or adult insects by their parents. But others continue eating insects as the main bulk of the diet when they are adults. Many strategies are used to catch these insects, and an understanding of the basics is a good first step to bird identification. Here are some of the main techniques.
Aerial ‘trawling’ and pursuing
This is the sort of strategy used by Swifts and hirundines, which are constantly in the air, catching flying insects with their wide open gapes. Similarly Nightjars chase moths and other insects on the wing. Hobbies are also aerial insect chasers, but tend to go for larger targets, such as dragonflies, and use their talons to pluck them from the sky.
Sallies from a perch
This is the classic technique of, for instance, the Spotted Flycatcher, swooping from an exposed perch after a flying target, grabbing it with a snap of the bill and returning to the same perch.
Picking from water surface in flight
Many adult insects make their first flight direct from water, having developed aquatically. These newly emerged insects are easy pickings for some birds. For instance, terns (especially marsh terns), Little Gulls (but also Black-headed Gulls), feed in flight, swooping down to pick from the water surface. Other birds, such as phalaropes (swimming waders) and smaller grebes, will also pick insects from the surface, while swimming.
Snatching on ground from a perch
Birds such as Stonechats and Whinchats and other chats, as well as shrikes, use raised perches to keep an eye out for moving insects (including caterpillars), then dive down to grab them and return to a raised perch, or eat the prey item on the ground.
Gleaning
Many birds, such as tits and warblers, spend a lot of time exploring every nook and cranny of trees, bushes and other vegetation looking for caterpillars, insect eggs and adult insects.