World’s insectivorous birds eat 400 to 500 million metric tons of beetles, flies, ants, moths, aphids, grasshoppers, crickets and other arthropods per year, according to a review of 103 previous studies.

Birds, represented by nearly 10,700 species, are found across the world in all major land ecosystems. They exhibit a large variety of life styles and foraging behaviors.

While some birds depend mainly on plant diets, such as seeds, fruits, and nectar, others feed as carnivores on animal prey, or as omnivores on a mixed diet of plant/animal matter. Most bird species (more than 6,000 species) are insectivores that depend for the most part on insects as prey.

“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,” said lead author Dr. Martin Nyffeler, a researcher at the University of Basel, Switzerland.

“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.”

Birds actively hunt insects especially during the breeding season, when they need protein-rich prey to feed to their nestlings.

“The global population of insectivorous birds annually consumes as much energy as a megacity the size of New York,” Dr. Nyffeler noted.

“They get this energy by capturing billions of potentially harmful herbivorous insects and other arthropods.”

Birds in forests account for over 70% of the global annual prey consumption of insect-eating birds (about 300 million tons per year), whereas birds in savannas, grasslands, croplands, deserts, and Arctic tundra are less significant contributors (about 100 million tons of insects per year).

“The estimates emphasize the ecological and economic importance of insectivorous birds in suppressing potentially harmful insect pests on a global scale — especially in forested areas,” Dr. Nyffeler said.

“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.”

The team also estimated that the world’s insectivorous birds have a total weight of around 3 million tons.

“The comparatively low value for the global biomass of wild birds can be partially explained through their very low production efficiency,” Dr. Nyffeler said.

“This means that respiration takes a lot of energy and only leaves about one to two percent to be converted into biomass.”

The findings will be published in the August 2018 issue of The Science of Nature.

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Martin Nyffeler et al. 2018. Insectivorous birds consume an estimated 400–500 million tons of prey annually. The Science of Nature 105: 47; doi: 10.1007/s00114-018-1571-z