BIRDS around the world eat up to 500 million tonnes of bugs a year, highlighting the important role they play in keeping plant-eating insect populations under control.
The number of beetles, flies, ants, moths, aphids, grasshoppers, crickets and other anthropods was calculated in a study led by Martin Nyffeler of the University of Basel in Switzerland.
Nyffeler and his colleagues based their figures on 103 studies that highlighted the volume of prey that insect-eating birds consume in seven of the world’s major ecological communities known as biomes.
According to their estimations, published in the journal The Science of Nature, this amounts to 400 million to 500 million tonnes of insects a year.
The Swiss calculations are supported by a large number of experimental studies by research teams in a variety of habitats in different parts of the world.
Nyffeler says forest-dwelling birds consume about 75 per cent of the insects eaten. About 100 million tonnes are eaten by birds in savanna areas, grasslands and croplands, and those in the deserts and Arctic tundra.
The researchers estimated the birds themselves only have a biomass of about three million tonnes. Nyffeler says the comparatively low number can be partially explained through their low production efficiency. This means respiration takes a lot of energy and only leaves about one – two per cent to be converted into biomass.
“The estimates presented in this paper emphasise the ecological and economic importance of insectivorous birds in suppressing potentially harmful insect pests on a global scale,” Nyffeler says.
This is especially so for tropical, temperate and boreal forest ecosystems.
“Only a few other predator groups such as spiders and insect-eating insects (including predaceous ants) can keep up with the insectivorous birds in their capacity to suppress plant-eating insect populations on a global scale,” he says.
A study that Nyffeler led last year found spiders consume between 400 million and 800 million tonnes of insects a year. Other predator groups like bats, primates, shrews, hedgehogs, frogs, salamanders, and lizards seem to be valuable yet less effective natural enemies of plant-eating insects.
“Birds are an endangered class of animals because they are heavily threatened by afforestation, intensification of agriculture, spread of systemic pesticides, predation by domestic cats, collisions with man-made structures, light pollution and climate change,” Nyffeler says.
“If these global threats cannot soon be resolved, we must fear that the vital ecosystem services that birds provide – such as the suppression of insect pests – will be lost.”