State’s bird population in decline, according to study

common yellowthroat
The common yellowthroat declined 79 percent since 1989, the largest drop among 34 species analyzed. Courtesy photo by K.P. McFarland
Fewer birds appear to live in Vermont today than 25 years ago, according to recent research by the Vermont Center for Ecostudies.

The most dramatic declines in bird populations were seen among those that live off flying insects, scientists say. Known as aerial insectivores, this diverse group of birds has declined 45 percent in Vermont, according to the study.

The study focused on 11 species of aerial insectivores that were among the 13 species of Vermont birds found to have undergone the most serious declines, said Steve Faccio, one of the study’s authors and the co-founder of the Vermont Center for Ecostudies.

This group of birds includes the tree swallow, the yellow-bellied flycatcher, the chimney swift and the eastern wood pewee.

This dropoff in insect eaters mirrors a trend seen nationwide in recent decades, Faccio said.

These birds’ food — aerial insects — is what the species in this highly varied group have in common, leading scientists to suspect that some widespread trend among flying insects is what’s driving the decline in birds that eat them, Faccio said.

Scientists say the decline might also be attributable to polarized light pollution and to a possible recent mismatch in timing between important points in the birds’ and the insects’ life cycles, Faccio said.

Natural polarized light is found most often reflected off the surface of water, but a variety of artificial surfaces reflect polarized light as well, such as windows, painted automobiles and even black plastic sheeting, according to the study. Because many insects are drawn to polarized light, scientists believe that some of them confuse highways for rivers, and that similar mistakes on a larger scale may be among the drivers of a decline in aerial insect populations.

white-throated sparrow
A white-throated sparrow. Courtesy photo by Steve Faccio
Mismatched timing between species can occur when global warming or other climatological occurrences lead insects to hatch earlier than normal, Faccio said. If they’re hatched and flying before the birds that eat them are active, aerial insectivores may be running out of food simply because of a timing issue, he said.

But there’s not enough information about insects yet to say whether their numbers have declined across the board, Faccio said. Population trends are known for some insect species, but aerial insectivores live off thousands of different species of insects, and it’s still unknown whether the diminishing population of aerial insectivores is matched by a drop in their food source, he said.

Vermont’s wind turbines are not thought to have any appreciable effect on the bird populations studied, Faccio said.

Other factors are thought to have contributed to the decline in bird numbers, said Faccio. These include pesticides and loss of habitat due to development.

Scientists have identified a number of potential causes for the decline, but there’s no consensus yet as to which is most responsible, Faccio said.

Although the number of aerial insectivores in Vermont appears to have dropped significantly, other groups of birds were found to have grown in number, according to the study.

Those include ground gleaners, a type of bird that plucks insects from the ground, such as the hermit thrush, the yellow-shafted flicker and the ovenbird. Another is the high-canopy foragers, including the bay-breasted warbler, the cerulean warbler and the scarlet tanager. Those groups grew by 22 percent and 11 percent over the 25-year study’s duration.

The study includes 125 species detected at about 30 study sites around Vermont, Faccio said. Each location contains five predesignated sites where volunteers and VCE staffers tallied how many and what type of birds could be seen or heard over a 10-minute period, he said.

For the first five years after the study began, researchers saw on average 14.8 individual birds at each of these sites during a single 10-minute observation period. For the five years leading to 2013, the last year the study concerns, researchers found an average of 12.7 individual birds per site — a 14.2 percent decrease.

The decrease occurred mainly during the first half of the 25-year period covered in the study, Faccio said.

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  • sara meling

    Hi Mike,
    I have for a dozen or so year been calling around to bird seed companies & their distributors to determine the percentage of GMO seeds in the mixes or single seed bird feed. So it varies but their is quite a bit and finding a manufacturer that has non-gmo bird seed is obscenely expensive. Additionally when I have called non profits / organizations that deal with GMO/environment/birds everyone uniformly goes – oh boy that’s amazing – never thought about the use of gmo’s in bird seed, the use of bird seed as a distribution channel for gmo’s, the impact of all those seeds been spread around via the digestion / elimination of seed, etc.
    Help and a hug if you can effect more study understanding of the impact of gmo bird seed and some way of stopping it.

  • George Plumb

    How sad that the authors don’t even mention the fact that it is not just a decline in bird population but we are now in what is called the Sixth Great Extinction or the Anthropocene period of the Earth’s Evolution. And it is all caused by human over population which the Vermont Center for Eco Studies, like most environmental organizations refuses, to acknowledge. This is why they are failing to truly protect the environment. But hey they are enjoying traveling all over the world in jet planes, adding to global warming,, but feeling good and making good money in the process. How long before the human species also goes extinct? Just Google sixth great extinction and what you will find should shock you. Just one example:

    “The modern world is experiencing a “sixth great extinction” of animal species even when the lowest estimates of extinction rates are considered, scientists have warned. The rate of extinction for species in the 20th century was up to 100 times higher than it would have been without man’s impact, they said….”.
    Humans creating sixth great extinction of animal species …

    • Stewart Clark

      I surely agree we are experiencing the “sixth great extinction” of life forms on Earth. I also agree humans need to recognize their overpopulation. However, I strongly disagree the Vermont Center for Eco Studies is responsible for these problems. If anything, they are shedding light on the issues.

      • George Plumb

        No Vermont Center for Eco Studies is not responsible for dealing with population growth but they should at least acknowledge that population growth is the underlying cause of our sixth great extinction which they have refused to do for many years.

        And I do strongly support the Sierra Club because they are the only Vermont environmental organization, besides Vermonters for Sustainable Population, that does publicly recognize that population growth is a problem. I do disagree with their organizing jet plane trips all over the world.

    • Kathy Leonard

      Whereas population is your focus, George, VCE focuses on wildlife and habitats. I’d hope you could promote your efforts without feeling the need to denigrate theirs.

      I have found the Vermont Center for Ecostudies to be a very effective advocate for wildlife and habitats, one of few groups that stay true to their mission while they also educate us humans and utilize citizen science to the utmost. They fly south to identify and work with others to protect wintering bird habitats, whereas the Sierra Club (which you promote) sponsors nature tourism all over the globe, which they surely raise money doing.

      The birds and the insects they depend on will benefit from VCE’s work as they adapt to and/or seek refuge here. To paraphrase Paul Watson, they “work for bumblebees and bobolinks.”

  • Did the researchers look at habitat loss or other factors in the birds’ winter nesting locations? I was looking at the decline in our nighthawk population a few years back. Nighthawks overwinter as far south as Uruguay, and I learned that their habitat there was being rapidly converted to ranches.

    • Tory Rhodin

      Yes, they did/do.

  • James Rude

    I was curious if the decline in bird population has occurred at the same level in the surrounding states and Canada or is this just a VT phenomena.

  • Felicia Scott

    Let’s just keep building industrial wind turbines that destroy habitat,contribute to fouling the air and slice birds to bits. They are good at killing bats too. Pretty soon Vermont will be an environmentally sterile place and that should make the windies so very happy!
    A nice row of really big wind turbines along the Burlington waterfront would go a long way to eliminating any problems with seagulls.

  • I guess it’s not just the young folks leaving the state.