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Bird multitudes are slipping away on a global scale, but a new study offers hope for how we can be better neighbors to feathered friends.
Researchers at Cal Poly San Luis Obispo knew, like everyone else in the bird world, that 3 billion birds have been lost in the last half century, but they wanted to know more about why. So they looked at changes in air pollution, light pollution, summer heat and eight other environmental and demographic conditions that affect birds.
To their surprise, they found some species are doing well in some places with bad air or bright nights, thanks to what nature put in the birds’ survival toolkit.
“Our study shows pretty convincingly that we are losing birds in some places, but we’re also gaining birds at local populations in other areas, so it’s not dire across the board.” said Clinton Francis, a Cal Poly biological sciences professor and co-author on the new study published in Current Biology.
In some parts of the West that have bad air pollution, Oregon juncos and spotted towhees actually had more babies. It could be because they spend much of their their day hopping from place to place, avoiding the respiratory stress of smoke that afflicts more athletic species.
In Southern California, the numbers of American robins and goldfinches increased in urbanized areas. Robins do well in grassy fields with scattered trees, which city parks often provide, the researchers said via email.
“I don’t think anyone’s going to dispute that we’ve lost a lot of birds across a lot of different populations. But I also find a lot of hope in our study,” Francis said.
Of the 11 stressors the researchers examined, two had the biggest overall negative effect on birds: less darkness at night and worse air pollution.
They found this hopeful because they are conditions that people can change locally.
Reducing misdirected street lighting for example can really help, especially in areas with species that need low light for navigation. Turning off lights when you leave the house is also good for birds.
“I’m looking out my window right now and I can see all kinds of sources of light at night that could be better shielded, just shining to illuminate plants. Which can look really nice at night, but also, the plant doesn’t need light at night,” Francis said.
Anything people can do to reduce fire risk can also lead to less air pollution, benefiting birds, the researchers said.
The fact that air and light pollution turned out to be among the strongest factors in bird decline wasn’t much of a surprise to Allison Shultz, associate curator of ornithology at the Natural History Museum of Los Angeles County.
“It basically matches a lot of observations that we’ve had over the years. It’s just it’s really nice to see it actually confirmed with real data and statistics,” she said.
Shultz was not affiliated with the study. But the museum has a collection of bird skulls that was included in its dataset. That’s because birds with larger eyes can absorb more light, giving them the upper wing when light is low.
To carry out the study, researchers needed to understand two main things: where bird numbers were rising and falling, and how the conditions around them had changed.
To look at the bird numbers, they used data collected from more than 350 bird banding research stations across North America that are little-known outside of birding circles. During a bird banding survey, a field team stretches nets between trees or chaparral to capture birds as they commute through their habitat. They gently pluck them from the netting and attach bird-sized bracelets to their scaly ankles.
They track numbers of adults and babies and how babies-per-adult changes over time by counting how many fly into the nets. A bird’s age, wing length and other fitness metrics are also recorded before it is released. Etched onto each of the bands is a series of letters and numbers that, if it’s captured again, tells the next researcher where this bird has been.
The dataset from the stations takes in 46 species common to North America. In this study, the researchers used close to 600,000 of these data points.
“We’re lucky in the world of birds that we have lots of different large scale data sets collected oftentimes by you know just everyday individuals,” said Dr. Sarah Jennings, lead author on the study and a postdoctoral researcher at Cal Poly. Jennings noted they used only species that could be captured in nets for banding surveys. Think small song birds you could see in a park or your backyard.
The researchers compared places where bird numbers were changing with the 11 conditions, using data sets for air quality, light and climate, among others.
Shultz said the strength of the study is its continental scale and data that spans decades. The tradeoff for working at such scale is lack of local detail, however. One example would be that the study annualized the conditions found on the days researchers strung their nets.
“If we looked outside the day after the Fourth of July, the air looked a lot different than it does when you look outside today, or if there happens to be a wildfire nearby,” she said.
Shultz also leads a community science effort to study how bird behavior may change when wildfire rolls through a region. Project Phoenix asks volunteers from western states to observe birds in their area each week and submit what they see through eBird, a popular birding app. She is currently analyzing data from last year’s fire season, and expects to have results soon.
”I’m actually really excited to see, as we’re looking at our Project Phoenix results and at wildfire smoke, you know, are these matching the broader trends that they’re seeing?”
This story originally appeared in Los Angeles Times.
