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Is Constant Human Noise Stressing Out Wildlife?

Animals
Is Constant Human Noise Stressing Out Wildlife?
Dave Keeling

By Jason Daley

A major study earlier this year showed something incredible. Looking at 492 protected areas in the U.S., researchers found that 62 percent of the parks, wilderness areas and green spaces were twice as loud as they should be. About 21 percent were 10 times as loud. Noise isn't just annoying—chronic exposure to traffic, generators and airplanes can lead to negative consequences for wildlife. Researchers like Nathan Kliest are just getting a handle on exactly how all that noise impacts animals. Kliest, formerly of the University of Colorado Boulder and now at SUNY Brockport, recently investigated the impact of chronic noise on birds in the Southwest.


Kleist and his colleagues found that a perfect experiment was already underway in the San Juan Basin of northern New Mexico. While much of the area is owned by the Bureau of Land Management and is uninhabited, the piñon and juniper flats are dotted with gas-extraction wells. While some of the wells run more or less silently, others have very loud compressors that emit a nonstop hum in a range that overlaps with the frequency of many bird vocalizations.

In a previous study, researchers had already looked at how the noise from these compressors affects birds, finding that the constant hum altered which birds nested in the nearby area. Noise-tolerant species moved closer to the sites while more sensitive species fled the area. But Kleist wanted to examine the physiological effects of noise pollution on the birds.

He built 240 nest boxes by hand and placed them at 12 pairs of gas wells in the Rattlesnake Canyon Habitat Management Area. One site in each pair had a droning compressor while the other was more silent. Then, over the course of three years, he monitored three cavity-nesting species that used the boxes: the western bluebird, the mountain bluebird and the ash-throated flycatcher. Kleist collected blood samples from adult female birds and chicks and assessed the body size and feather length of nestlings each breeding season.

The results, reported in The Proceedings of the National Academy of Sciences, showed that mountain bluebirds avoided the noisy areas, and flycatchers also kept their distance, though they were a little more tolerant. Western bluebirds, however, seemed fine with increased noise levels and nested everywhere on the sites. But that doesn't mean they were unaffected. Nestlings in high-noise areas had smaller body sizes and reduced feather growth.

So why would a bird choose to nest in a noisy area? Researchers aren't certain, but it's possible some birds are attracted to noise because it keeps away predators and other species competing for resources, creating an exploitable niche. While this might be an evolutionary advantage under normal circumstances, it could be an "ecological trap" when it comes to human-generated noise, leading the birds to make harmful choices.

Kleist said it's possible that the drone of the compressor drowns out the calls of other birds, which mother bluebirds rely on to tell them whether predators like scrub jays and bobcats are present. "It's possible birds in loud habitats have less perception and knowledge of their environment and have to spend more time and energy figuring out what is going on," he said. "A mother bird in a loud box might be leaving the nest box more often and might not be brooding as much so the temperature wavers."

The team also found something unexpected: All the birds nesting in noisy areas had lower baseline levels of corticosterone, a key stress hormone. "I was really surprised," said Kleist, who thought the birds' stress hormones would be through the roof. "I saw these decreasing baseline stress hormones while seeing decreasing reproductive and hatching success in western bluebirds. It was a juxtaposition of results I didn't expect."

But the result made sense to Christopher Lowry, a stress physiologist at CU Boulder and coauthor of the paper. "You might assume this means they are not stressed. But what we are learning from both human and rodent research is that, with inescapable stressors, including post-traumatic stress disorder in humans, stress hormones are often chronically low," he said in a statement. Stress leads to hypervigilence or the "fight or flight response." However, most organisms cannot sustain that heightened state for very long. So the body down-regulates stress hormones to conserve resources, leading to hypocorticism, which causes increased inflammation and reduced weight gain, at least in tests on rats.

"That's an insight into conservation physiology that his study tightens," said Kleist. "These results are maddeningly all over place. But any disregulation suggests chronic stress."

There is still a lot to work out about how exactly noise impacts wildlife and human health, but Kleist said there's mounting evidence that it's an element policymakers and land managers need to begin thinking about. "Noise might not be good for wildlife or humans. It reduces the value of habitats like parks," he said. "To make them as valuable and useful as possible to wildlife, we need to consider the impact of noise."

Reposted with permission from our media associate SIERRA Magazine.

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A net-casting ogre-faced spider. CBG Photography Group, Centre for Biodiversity Genomics / CC BY-SA 3.0

Just in time for Halloween, scientists at Cornell University have published some frightening research, especially if you're an insect!

The ghoulishly named ogre-faced spider can "hear" with its legs and use that ability to catch insects flying behind it, the study published in Current Biology Thursday concluded.

"Spiders are sensitive to airborne sound," Cornell professor emeritus Dr. Charles Walcott, who was not involved with the study, told the Cornell Chronicle. "That's the big message really."

The net-casting, ogre-faced spider (Deinopis spinosa) has a unique hunting strategy, as study coauthor Cornell University postdoctoral researcher Jay Stafstrom explained in a video.

They hunt only at night using a special kind of web: an A-shaped frame made from non-sticky silk that supports a fuzzy rectangle that they hold with their front forelegs and use to trap prey.

They do this in two ways. In a maneuver called a "forward strike," they pounce down on prey moving beneath them on the ground. This is enabled by their large eyes — the biggest of any spider. These eyes give them 2,000 times the night vision that we have, Science explained.

But the spiders can also perform a move called the "backward strike," Stafstrom explained, in which they reach their legs behind them and catch insects flying through the air.

"So here comes a flying bug and somehow the spider gets information on the sound direction and its distance. The spiders time the 200-millisecond leap if the fly is within its capture zone – much like an over-the-shoulder catch. The spider gets its prey. They're accurate," coauthor Ronald Hoy, the D & D Joslovitz Merksamer Professor in the Department of Neurobiology and Behavior in the College of Arts and Sciences, told the Cornell Chronicle.

What the researchers wanted to understand was how the spiders could tell what was moving behind them when they have no ears.

It isn't a question of peripheral vision. In a 2016 study, the same team blindfolded the spiders and sent them out to hunt, Science explained. This prevented the spiders from making their forward strikes, but they were still able to catch prey using the backwards strike. The researchers thought the spiders were "hearing" their prey with the sensors on the tips of their legs. All spiders have these sensors, but scientists had previously thought they were only able to detect vibrations through surfaces, not sounds in the air.

To test how well the ogre-faced spiders could actually hear, the researchers conducted a two-part experiment.

First, they inserted electrodes into removed spider legs and into the brains of intact spiders. They put the spiders and the legs into a vibration-proof booth and played sounds from two meters (approximately 6.5 feet) away. The spiders and the legs responded to sounds from 100 hertz to 10,000 hertz.

Next, they played the five sounds that had triggered the biggest response to 25 spiders in the wild and 51 spiders in the lab. More than half the spiders did the "backward strike" move when they heard sounds that have a lower frequency similar to insect wing beats. When the higher frequency sounds were played, the spiders did not move. This suggests the higher frequencies may mimic the sounds of predators like birds.

University of Cincinnati spider behavioral ecologist George Uetz told Science that the results were a "surprise" that indicated science has much to learn about spiders as a whole. Because all spiders have these receptors on their legs, it is possible that all spiders can hear. This theory was first put forward by Walcott 60 years ago, but was dismissed at the time, according to the Cornell Chronicle. But studies of other spiders have turned up further evidence since. A 2016 study found that a kind of jumping spider can pick up sonic vibrations in the air.

"We don't know diddly about spiders," Uetz told Science. "They are much more complex than people ever thought they were."

Learning more provides scientists with an opportunity to study their sensory abilities in order to improve technology like bio-sensors, directional microphones and visual processing algorithms, Stafstrom told CNN.

Hoy agreed.

"The point is any understudied, underappreciated group has fascinating lives, even a yucky spider, and we can learn something from it," he told CNN.

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