Grubbing around
INSECTS are essential food for a large proportion of the bird species in the world.
It has been estimated that 90% of Palearctic landbird species feed on insects in the breeding season. In tropical regions an estimated 60% are insectivorous. An estimated 400 million tonnes of insects are eaten every year by birds, with forest species eating about 70% of them.
Britain’s woodlands contain a huge amount of insect life and certain trees are especially valuable. The English Oak is known to support 284 insect species, the various willows host more than 260 species, Silver Birch 229, and Common Hawthorn up to 149. Among conifers, Scots Pine scores highest, with 91 species. The Blue Tit population of Britain and Ireland has been calculated to eat 50 billion moth caterpillars every year.
With so many birds eating insects, it is no wonder there are many different methods used to forage for them. Watching the ways in which different species feed is fascinating and many totally unrelated families have evolved identical feeding methods. Old World flycatchers and the tyrant flycatchers of the New World, as well as the monarchs of Africa, Asia and Australasia, all catch insects by ‘hawking’. Many species will use more than one method to ensure they are well fed.
Here are some of the different methods of feeding on insects by landbirds.
Gleaning
This is the process of finding invertebrate prey by searching the branches and leaves of trees and bushes. This method can vary from fairly slow and methodical to extremely active, and most species which use this method are fairly small with fine beaks for picking out their prey. Both adult insects and larvae are taken in this way.
Many European woodland warblers such as Common Chiffchaff and Blackcap feed by gleaning. A bird may flutter or hover in the air to pick off an insect, a particular technique of the tiny Goldcrest. Small birds, like Blue Tits, can hang underneath the end of a twig to take prey items, with aphids being a particular favourite. Many species, including treecreepers, nuthatches and tits, will actively search in crevices to find insects and grubs, and may have longer beaks to achieve this.
One study which compared Nearctic and Palearctic gleaning methods found that species in the Nearctic gleaned mostly leaves, while Palearctic species foraged on a higher proportion of twigs and branches. This is due mainly to the preponderance of conifer species and associated prey in the Nearctic.
Other forms of gleaning can take place on the ground, with birds searching through leaf litter for prey; Common Starlings search lawns, probing down with their beaks for cranefly larvae. Dipper is unusual, foraging for caddisfly larvae underwater.
Fly catching
This method, sometimes called aerial hawking, is practiced by a wide variety of species. It involves watching from a perch and darting out to catch a passing flying insect, often returning to the same perch or another nearby. Sometimes the prey item is not caught with the initial sally and may be actively chased until captured. Usually only one prey item is chased and captured at a time. In Britain Spotted and
Pied Flycatchers feed like this and even Little Owls will fly out to catch flying prey up to small beetle size.
Most species will land with their prey before eating it, but a small gnat may be consumed in flight. Eurasian Hobby will catch a dragonfly in flight with its talons, and eat it while flying, holding it with its feet. Bee-eaters catch wasps and bees, flying back to a perch and knocking them to remove the sting; Spotted Flycatchers do the same. European Nightjars fly from a perch or the ground after a moth and will also forage in quite lengthy flights with much twisting and turning. Opportunistic flycatching can be found in other species, such as Chaffinch and Waxwing.
Aerial foraging
Swifts, swallows and martins are the most efficient aerial foragers, catching most of their food on the wing. A House Martin will bring back a pellet of 50-100 insects to its young and a Common
Swift needs as many as 40,000 flying insects each day just for itself. Black-headed Gulls can be seen catching insects in the air when flying ants are on the wing, swooping aerobatically to grab them.
Ground foraging
Many species find their insect food on the ground, often watching from a vantage point.
Little Owls will locate prey from a perch, then fly down to catch it, sometimes landing and running or hopping to finally snap up an earwig or beetle. Common Kestrels may similarly catch grasshoppers. Green Woodpeckers spend a great amount of time on the ground feeding on ants, using their long tongues to sweep them up. Chris Harbard