Scientists Are Tracking Worrying Declines in Insects—and the Birds That Feast on Them. Here’s What’s Being Done to Save Them Both

In Vermont, researchers have investigated the types of creepy, crawly bugs that their avian predators consume and may have found the answers to keeping them both alive

July/August 2025

A veery gets ready to rise into the Vermont skies, not long before setting off on an annual migration to the species’ wintering grounds in Brazil. Melissa Groo

Key takeaways: Why birds and bugs have a shared fate

Most bird species (90 percent) rely on insects for food at one point during their lives.
Bugs provide a critical role in their ecosystem, no matter where on the planet they live, providing food for other bugs, birds, mammals and humans. They are vital to the survival of life on Earth.

Less than two hours after sunrise, with the shadows still blue and slanting hard in a dense growth of balsam firs and spruces, the baby bird blundered into a fine black net strung along the ridgeline of Mount Mansfield, at 4,393 feet Vermont’s tallest mountain.

Desirée Narango, a conservation scientist with the Vermont Center for Ecostudies, or VCE, retrieved the rescued bird and with practiced fingers spread one of its wings like a fan. From the bird’s mottled and rumpled feathers, Narango could see that this slate-colored bird was a dark-eyed junco, a sparrow species found in various color combinations across North America. The bird was just a few weeks out from leaving its nest. It was too young to tell its sex. But she was less interested in the bird itself than in what it had been eating.

Juncos are known as seed-eating birds. They spend their days rummaging through the undergrowth searching for fallen seeds. At feeders, they prefer smaller grains, like millet. But seeds don’t provide the protein juncos, or any songbirds, need to grow a new set of feathers while they molt. And the protein this baby junco needs to molt its blotchy juvenile feathers and to grow sleek stone-gray feathers on top and white ones below would come only from bugs. In fact, 90 percent of the more than 10,700 known bird species rely on insects for food during at least part of their life cycle. Even the most dedicated seed-eating songbirds must eat insects and other arthropods, that many-legged group of creatures that includes spiders and millipedes, to produce eggs, to grow new feathers and to feed their young. Without insects, in other words, they wouldn’t survive.

A hemlock looper moth drawn to the backyard lights of a Cornell University entomologist in Ithaca, New York. Several songbird species in the region feed on its caterpillars, and other creatures eat the moths when they fall into the water or onto the ground. Melissa Groo

Desirée Narango, a scientist at the Vermont Center for Ecostudies, conducts field research on Mount Mansfield, the highest point in Vermont. The center has been studying avian population and health since 1992 and bands about 5,000 individual birds each year. Melissa Groo

Unfortunately, insects are disappearing at a rate of about 1 to 2 percent a year. And the decline is not limited to just one species nor just one group of insects. The data suggests that the decline is widespread, even global. These findings have been confirmed in hundreds of rigorous, peer-reviewed studies, says David L. Wagner, a University of Connecticut entomologist and the lead scientist of a program known as the Status of Insects, which coordinates pertinent research on insect populations from around the world. “The weight of the evidence is clear,” Wagner says. “I feel like it would stand up in a court of law.”

Narango, who is now one of dozens of researchers participating in the project, was a city kid from Baltimore, with her heart set on becoming a zookeeper. Her undergraduate program at the State University of New York College of Environmental Science and Forestry required a summer semester at a biological field station in the Adirondacks. She had never been camping or even to the woods. On the tree-crowded shores of a mountain lake, she was captivated by the bouncy, fluty song of an unseen bird. By the time she figured out that it came from a white-throated sparrow, her future had been mapped. Today, she investigates the relationship between the worldwide decline in insects and a worldwide decline in birds. The bird cradled in her hand up on Mount Mansfield holds some of the answers to the mystery behind these trends.

Bees, butterflies, moths, flies, beetles, ants and a few other insects pollinate three-quarters of the world’s flowering plants and crops. Their pollination services are worth up to $577 billion per year worldwide. Less well known is their critical role in helping dead things disappear—piles of leaves and rotting stumps, the rat in the street, the elephant on the savanna, the contents of your compost bin. Insects also feed on feces, cleaning up the messes of wild and domestic animals. Dung beetles provide $380 million a year in manure recycling for the American cattle industry. All of these clean-up activities create soil for new plant growth.

Cover image of the Smithsonian Magazine July/August 2025 issue

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This article is a selection from the July/August 2025 issue of Smithsonian magazine

A dark-eyed junco peers out of the foliage on Mount Mansfield. The species declined more than 30 percent between 1966 and 2019. The birds mostly eat seeds and grains, but at key times in their life cycle when they need more protein, they feast on insects. Melissa Groo

Insects feed many animals we eat, such as trout, salmon and turkeys. In some places they feed us directly—more than 2,000 species of insect are eaten by people around the world. And that’s not even considering honey. Bugs also keep each other under control. Ladybugs eat the aphids in your garden. Praying mantises eat flies, moths, roaches, grasshoppers and more. Dragonflies patrol the skies, eating flies, midges and mosquitoes. Some wasps are clever parasites, paralyzing other insects, including some we don’t like, to feed their young. Simply put, insects are vital for the survival of land-based life on this planet.

Ellen Welti, a research ecologist with the Smithsonian’s Great Plains Science Program, says there are two groups of people who study insects: those who look at them as pests or carriers of disease, and those who study insects’ roles in natural systems. While most insect researchers look for better ways to control grasshoppers on rangelands, Welti says, she studies how, for example, grasshoppers benefit grasslands, by providing enough fertilizer through their frass (that is, poop) to increase the yield of next year’s grasses, which outweighs the damage they do eating this year’s grasses.

A Bicknell’s thrush trapped in a net by researchers on Mount Mansfield. The birds can be found in mountainous areas in New England and eastern Canada. They eat ants, beetles, flies, moths and grasshoppers, along with spiders and snails. Melissa Groo

The Status of Insects project led by Wagner helps scientists like Welti fill gaps and coordinate their research. The network doesn’t just focus on the glamorous insects such as butterflies, bees and dragonflies. Jessica Ware, the curator of invertebrate zoology at the American Museum of Natural History in New York and one of the project’s principal investigators, leads a research group for cockroaches and termites. These insects are a nightmare in our homes but are part of nature’s intricate workings outside them. Only 2 percent of cockroach species are pests, while the other 7,000 or so species are benign, Ware says. (“Actually, a lot of them are really pretty,” says Eliza Grames, a biologist at Binghamton University and another project leader.) Similarly, termites, which are a kind of cockroach, break down old trees and are vital to tropical forest health. Everywhere, Ware says, they are an important food source for birds when they swarm during mating. She has even seen birds feasting on termite swarms in New Jersey.

The insect network project grew out of an earlier initiative by Grames, who started as a bird researcher and became an expert in large-scale data analysis, and an entomologist friend named Graham Montgomery. The researchers realized that many existing research papers tagged with insect data were actually calculations of birds’ food, so they designed a system to mine published research for data about insect population levels. “It was a weird series of events, and now, that’s everything I do,” Grames says.

Grames believes that repeating long-term studies from decades ago is critical for understanding why insects have declined. While some issues are known—for example, habitat loss, non-native plants, artificial light at night, climate and pesticides—scientists need to know a lot more about the drivers and consequences of the decline to conserve insects while protecting human needs.

Repeating previous bird and insect studies is what Narango is doing on top of Mount Mansfield. VCE scientists have been studying birds there since the 1990s. As the scientists weighed, measured and banded birds on Mount Mansfield, decade after decade, they also collected feathers, placing them in envelopes for future study. Those envelopes sit in boxes in a corner of VCE’s lab in the village of White River Junction.

A moth panel, a sheet placed out at night to lure and collect insects. Between monitoring insect populations and analyzing the compounds in avian feathers, the team is assembling an inter-connected picture of bird and bug health. Melissa Groo

Narango plans to have those feathers analyzed for the natural variations in their carbon and nitrogen isotopes, which will uncover clues about each bird’s diet. For example, she will be able to tell if it ate mostly plants and their seeds, or mostly plant-eating animals (such as caterpillars), or mostly animals that eat other animals (such as spiders).

To have a recent comparison, Narango’s team collects feathers from six bird species on Mount Mansfield, including juncos. Another scientist plucked a tail feather from the rumpled young junco and snipped off half of a still-attached wing feather, dropping the samples into a small manila envelope. Narango will analyze these feathers for carbon and nitrogen isotopes, too. Going one step further, Narango also pricked a vein in the junco’s wing and gathered a drop of blood in a capillary tube. After it is analyzed for isotopes, the blood sample will give her an even more recent snapshot of what the bird has been eating.

That is not all the bird had to offer. As it waited its turn to have its blood collected, it sat in a brown paper bag with a piece of filter paper on the bottom. Narango checked the bag and, yes, the baby junco had pooped there while it waited, leaving a grayish smear on the paper. This bird poop was scientific gold. Run through DNA analysis, it would tell Narango everything this bird had eaten in the last few hours, right down to the species. It’s a level of specificity that has only recently become available, and for scientists studying the interaction between birds and insects, it’s hard to beat.

As Narango and others collected data on the birds, Zoey Pickett, a VCE summer intern and undergraduate at Mount Holyoke College, tended the traps set for ground insects. Every week throughout the summer, Pickett emptied dozens of plastic cups that had been filled with a thick liquid preservative and buried in the ground up to their rims, waiting for crawling insects to stumble in. She folded the filter containing the insects and placed it first in a plastic bag, then in an empty plastic cat food jar and finally into her yellow backpack. Pickett said the multiple layers of packaging are vital, since slugs (mollusks, not insects) end up falling into the liquid, and their smell is uniquely bad.

Back in the lab, Amber Jones, a VCE technician, transferred the insect samples into a petri dish and examined them under a microscope. Carabid beetles, a type of ground beetle, were particularly interesting to the team because they were a focus of a University of Vermont researcher who gathered data on that spot 30 years ago. That researcher wrote a report just on Mount Mansfield’s carabid beetles, and Narango’s team is identifying each species to compare results. “They all look small and black,” Narango said, “but under the microscope, you can see the fine differences between them.”

Pairing 2 — Michael Hallworth, a data scientist from the Vermont Center for Ecostudies, draws blood from an ovenbird and plucks a feather from a blackpoll warbler. Both of these small songbirds breed in Vermont, though they spend much of the year in warmer climates—the ovenbird in Mexico and Central America, and the blackpoll warbler in South America. They eat mostly insects, which they find in the foliage or on the ground. Their winter diets down south also include fruits and berries. Melissa Groo

Jones sorted the creatures in the petri dish with a tweezer, placing a spider into one crimped-edged aluminum dish, the springtails into another and the mites—which lived up to their name—in a third. The dishes were labeled, dried in an oven at 140 degrees Fahrenheit for 24 hours, then weighed. The results gave the researchers a picture of which insects were available for a ground-feeding bird like the baby junco to eat the week the samples were collected.

The night before the baby junco landed in the research team’s net, a strange, shifting light filtered through the forest, not far from where the Long Trail, Vermont’s end-to-end hiking route, traverses the Mount Mansfield ridgeline. “I sometimes wonder if hikers going by think aliens have landed,” Narango said. A closer inspection would not have dispelled their suspicions. The source of the light, which shifted from blue to green to a white whose secret ingredient is ultraviolet, sat in the middle of what could have been an alien lantern, with the otherworldly lightbulb supported in a mystifying structure of translucent plastic.

tools — At the Mount Mansfield research station, supplies include leg bands, the tiny metal cylinders on the strands below, which are affixed to birds before they’re released. Each has a unique code so researchers can follow a single bird’s movements over the seasons. Melissa Groo

It was a moth trap, with a funnel below the light to catch the moths drawn in from the surrounding forest. Narango had furnished the five-gallon hardware store bucket that sat below the filter with a jumble of comfy cut-up egg cartons. The moths could rest among them before a jar of ammonium carbonate, also known as smelling salts or baker’s ammonia, hidden at the bottom of the bucket, killed them. “We are looking for non-lethal methods, but some species of moths you have to kill to identify,” Narango said. “And that’s what they were doing in the past, so we stuck with that.”

When she collected the bucket the next morning and searched through the egg cartons, she didn’t find much: one spectacularly patterned geometrid moth, better known for its inchworm caterpillars, and three micro leaf-roller moths. There was a caddis fly in the bucket, which is a type of aquatic insect, and a few tiny flies.

The haul let Narango know which caterpillars are available for birds on the mountain, as each of these moths was a caterpillar once. She doesn’t survey for butterflies because birds don’t eat them or their caterpillars often. Butterflies are colorful because they are typically toxic, or at least taste bad to birds, she explains. Not even their caterpillars make good baby-bird food. With their flashy colors, she says, “butterflies are just trying too hard.”

moth 3 — **A Vermont moth sampler:** The Bruce spanworm (top), the large maple spanworm (middle) and the common carpet moth (bottom). By asking volunteers to upload moth photos via an app called iNaturalist, the Vermont Center for Ecostudies has discovered 100 new species. Melissa Groo

Narango emphasizes that the poor catch is not an example of insect decline but a result of a particularly chilly summer night. This is what makes insect research so tricky. If Narango only sampled moths on this chilly night in early August, she would get a different idea than if she only sampled them on the warm night at the end of May, when moths were so plentiful on Mount Mansfield that they covered both the inside and the outside of the bucket. This is why she sets the light trap every week of the field season.

Though Narango and her colleagues don’t yet have a final count of moths and ground insects or their species, she noticed that they were collecting many fewer moths than the research team had 30 years ago. They collected their moths in a garbage can, Narango said. She was using a mere five-gallon bucket.

On the other hand, her team was collecting more carabid ground beetles than were present 30 years ago, and more of the beetles they collected were high-elevation specialists. “This may be a climate refugia,” Narango said, referring to a place that remains relatively unchanged during major shifts in climate. The top of Mount Mansfield has been spared from the development happening in the world below over the past 30 years.

Blood Sample — After collecting material in the field, Narango’s team sends it to a laboratory in White River Junction, about 80 miles south. A scientist fills tubes with blood samples drawn from birds on Mount Mansfield Melissa Groo

Specimens — Dehydrated and preserved specimens. Melissa Groo

Beetles — A tray of preserved beetles, pinned and labeled for reference. Melissa Groo

Narango has an idea of what’s ahead for the baby junco and the other birds on the mountain. She previously studied birds in cities, and she found that in places with fewer native plants, there were fewer protein- and fat-rich caterpillars, so the chickadees she studied turned to eating spiders, which are lower in fat, instead. In these places, the chickadees laid fewer eggs, and fewer hatchlings survived to leave the nest.

Grames’ research shows that the quantity of insects available to birds matters. When there are more insects in a habitat, she says, “birds raise fatter, happier chicks.” Chris Elphick, of the University of Connecticut, who now helps lead the Status of Insects network, says, “If you’re a swallow, maybe some insects are more like eating steak and two veg, and others are like eating lettuce all the time.”

Even knowing the strong evidence of global insect decline, neither Grames nor Narango despairs over the fate of birds and insects. They are optimistic that while they wait for policy changes, simple everyday actions can make a difference. They advise using fewer outside lights, which attract insects, distracting them sometimes to the point of death from starvation or exhaustion and making them vulnerable to predators like spiders. It helps when lights are motion-activated and yellow or another warm color, since insects are attracted to bright white light. They also recommend using fewer insecticides. Narango knows from her own research that planting native plants in a yard, or even in a pot on an apartment balcony, can help provide high-protein insect food for birds. Planting a single tree can make a difference, with an oak supporting up to 557 species of caterpillars.

Narango holds a Canada warbler, a species whose breeding range dips down below the Canadian border into New England and northern Pennsylvania. Melissa Groo

View — A view from Mount Mansfield in late summer. Melissa Groo

People may not be motivated to save the insects for their own sake, but a world without insects is a world without birds. It’s a world where no college student will hear the fluty song of a white-throated sparrow across a mountain lake and have her life changed. It’s a world where nature offers no song to the rising sun. It’s a silent spring.

In the long term, it would become something even worse. “Without insects, everything dies: all mammals, all reptiles, all birds and even humans,” Ware says. “If you want to conserve any of those other things, including us, you should want to conserve insects.”

What Narango did after making sure the junco’s needle prick had healed looked like a magic trick, but it came merely from years of experience. She fluttered her hands, a set of maneuvers to give the bird a firm launching pad, and suddenly, the junco was free. It flew into the blue shadows of a patch of balsam firs near the top of Mount Mansfield. It was time to find breakfast.

Editors’ note, July 10, 2025: A caption previously misidentified the invertebrate samples pictured; it has been updated to correct the error.

Scientists Are Tracking Worrying Declines in Insects—and the Birds That Feast on Them. Here’s What’s Being Done to Save Them Both

Key takeaways: Why birds and bugs have a shared fate

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