Birds around the world eat 400 to 500 million metric tons of beetles, flies, ants, moths, aphids, grasshoppers, crickets and other arthropods a year, according to an international study by Martin Nyffeler of the University of Basel in Switzer-
land.
The research, published in Springer’s journal The Science of Nature, highlights the important role birds play in keeping plant-eating insect populations under control.
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, this amounts to between 400 and 500 million tons of insects a year, but is most likely to be on the lower end of the range.
Their calculations are supported by a large number of experimental studies conducted by many different research teams in a variety of habitats in different parts of the world.
“The global population of insectivorous birds annually consumes as much energy as a megacity the size of New York.
"They get this energy by capturing billions of potentially harmful herbivorous insects and other arthropods,” said Nyffeler.
Forest-dwelling birds consume around 75% of the insects eaten in total by birds, which make up about 300 million tons of insects a year.
About 100 million tons are eaten by birds in savanna areas, grasslands and croplands, and those living in the deserts and Arctic tundra. Birds actively hunt insects, especially during the breeding season when they need protein-rich prey to feed to their nestlings.
Further, the researchers estimated that insectivorous birds together only have a biomass of about 3 million tons.
Nyffeler said the comparatively low value for the global biomass of wild birds could be partially explained through their very low production efficiency. This means that respiration takes a lot of energy and only leaves about 1% to 2% 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 - especially in forested areas,” said Nyffeler.
He added that this was especially so for tropical, temperate and boreal forest ecosystems.
“Only a few other predator groups such as spiders and entomophagous insects (including in particular predaceous ants) can keep up with the insectivorous birds in their capacity to suppress plant-eating insect populations on a global scale.
“Birds are an endangered class of animals, because they are heavily threatened by factors such as afforestation, intensification of agriculture, spread of systemic pesticides, predation by domestic cats, collisions with man-made structures, light pollution and climate change.
"If these global threats cannot soon be resolved, we must fear that the vital ecosystem services that birds provide will be lost,” said Nyffeler.