The early bird catches the worm — and, one UC Irvine scientist says, might also help reduce the effects of global warming.

Eastern bluebird with leaf-eating caterpillar. Photo by Mike Onyon.

In a new study published in a scientific journal this week, ecologist and lead author Kailen Mooney shows that birds, bats and lizards consume enough insects to reduce the damage they cause to plants and promote plant growth — by 14 percent on average.

“The goal was to understand how natural communities work, and the role of top predators in shaping and affecting communities of insects,” Mooney said.

The study itself, a “meta-analysis” of 63 previous studies involving 113 experiments, looked only at how plant growth is affected by removing birds and other animals that prey on insects. But the implications for climate change are clear, Mooney said.

“Anytime a plant is growing, it’s taking carbon dioxide out of the atmosphere and turning it into tissues,” he said.

Humanity’s release of carbon dioxide, along with other greenhouse gases, is believed by climate scientists to be driving the sharp warming trend seen in global temperatures.

The more carbon stored by plants, the less in the atmosphere. That could help slow down the rise in temperatures.

Although the estimate is not part of the study, Mooney said the rate of increased carbon capture could parallel the amount of increased plant growth promoted by birds and other insect predators.

“From the fact that there are predators protecting plants, and increasing the growth rate by approximately 14 percent, it’s a rough approximation to say it is increasing carbon capture in natural ecosystems on something on the order of 14 percent also,” he said.

Mooney and his co-authors spent four years combing through every study they could find that involved keeping birds, bats or lizards away from plants to see if there was an effect on plant growth-rates.

That includes experiments Mooney himself did as a graduate student in the pine forests of Colorado.

Mooney built cages around pine trees to keep birds out, then tracked insect populations and tree growth for three years.

“We found that, in a nutshell, birds increased the growth rate of pine trees by about a third,” he said.

But while a number of such experiments had been done, no one had yet pulled them all together for an overall analysis.

One of his most important findings, he said, was that the effects of insect predators on plant growth showed wide variation depending on type of habitat — trees or shrubs, for example — as well as latitude, with strong differences between tropical and temperate zones.

He also found that the growth-promoting effect held up even though the birds, bats and lizards were feeding not only on insects but other insect predators, such as spiders.

“It wasn’t clear how strong that would be,” he said. “Maybe it would turn out to be a wash.”

But he found plant growth was enhanced by about the same amount, even when consumption of other insect predators was taken into account.

The study also has implications for wildlife conservation, he said. Bird populations are declining in many places because of loss of habitat. And great care must be taken when growing new forests to capture carbon dioxide, he said, so that “at the same time we’re trying on one end to increase carbon capture by planting new forests, we’re not losing populations of these predators, and maybe sliding backwards in that regard,” he said.

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