A great many birds eat a great many bugs: this is something that, in general, we already know. But just how much do they eat? Empirical figures are hard to come by — but according to a new estimate, published in the journal The Science of Nature, the total figure is truly breathtaking, roughly equivalent to the weight of meat and fish consumed each year by humans.
Calculated by researchers led by biologist Martin Nyffeler of Switzerland’s University of Basel, the estimate draws upon earlier studies describing what each bird species eats, how much energy they require, and how many of them there are. Nyffeler’s team concludes that the total biomass of wild bird-consumed insects amounts to some 400 million tons.
As aforementioned, that’s about as much animal flesh as is eaten by people. Or, to make another comparison, Nyffeler’s team puts the weight of all those insect-eating birds together weigh at 3 million tons: on average, then, individual birds consume more than 100 times their own body weight in bugs.
The figure underscores the magnitude of ecosystem services provided by insectivorous birds, says Nyffeler; many of those bugs are considered pests, and predation helps regulate their populations and prevent outbreaks. At a more subtle ecological level, predation helps maintain dynamics that promote long-term species richness and abundance.
The total biomass of wild bird-consumed insects amounts to some 400 million tons
Putting a monetary value on this extraodinary labor is difficult — no global estimate exists, though various studies give locale-specific figures, such as $4,000 per hectare of enhanced production in Jamaican coffee plantations or nearly $1,500 per kilometer of worm control in northwestern U.S. commercial forests — but the figure, says Nyffeler, is undoubtedly vast.
He hopes these numbers will draw attention to the plight of insect-eating birds, many species of whom are declining or endangered. Habitat loss, widespread pesticide use, hunting, infrastructure mortality and predation by free-ranging cats are to blame. “If these global threats cannot soon be combated,” Nyffeler says, “we must fear that the vital ecosystem services that birds provide will be lost.”
For now these values go mostly unacknowledged in the management of natural systems, particularly by industries that profit from the birds’ labor. Much of their insect consumption happens in forests, yet forestry companies generally don’t manage habitat with insect-eating birds in mind, much less protect migratory insect-eaters elsewhere on their journeys.
“From a point of view of forestry a rethinking is urgently needed,” Nyffeler says. Commercial forests, which so often are tree plantations containing just a few species, “should be replaced by near-natural forests” that “provide appropriate habitats for a high number of forest songbird species.”
The researchers also point out another nuance to their study: in addition to describing the importance of birds for regulating insects, the findings also demonstrate how important insects are for birds. Many recent studies have described a precipitous decline in global insect populations — a trend that Nyffeler calls “frightening.” “We need to find out all about the extent and cause of this phenomenon,” he says.
Source: Nyffeler et al. “Insectivorous birds consume an estimated 400–500 million tons of prey annually.” The Science of Nature, 2018.
About the author: Brandon Keim is a freelance journalist specializing in animals, nature and science, and the author of The Eye of the Sandpiper: Stories From the Living World. Connect with him on Twitter, Instagram and Facebook.