On October 17th, 2017 we learned about

A history of air pollution recorded on preserved bird bellies

History is usually studied in written records, man-made objects, rocks and bones. It’s no surprise that we generally rely on durable materials like this, but more studies of more recent history aren’t so limited. Thanks to careful preservation of biological samples from around 200 years ago, we can use softer, more delicate bits of biology to find out what was happening in the world, including picking up evidence of very indelible events, like air pollution from the industrial revolution. In that case, instead of looking at stone or tools, researched dug into museum collections to survey thousands of dead, but preserved, birds.

By the 1870s, parts of the United States were being overwhelmed by smoke from furnaces and steam engines. These early combustion engines opened up a lot of new possibilities in technology, but they also dumped a lot of soot on their surrounding neighborhoods. By 1874, places like Chicago were so choked with smoke that it obscured the Sun on a daily basis, a scenario we usually associate with natural disasters. These smokey years have been documented in some forms, but biologists wanted to find data on air pollution across a wider territory and time span. The record they then turned to was the accumulated soot that was still stuck to the feathers of birds collected from the 1800s to the present day.

Documenting accumulated dirt

The researchers traveled to museums around America’s so-called Rust Belt to compare as birds across different decades and locales. Instead of taking samples of soot for chemical analysis, they measured the overall level of contamination on a bird’s body by taking photos, then quantifying exactly how dark its white feathers had become. To make sure varying light levels or human error didn’t throw off these measurements, each bird was placed next to a paint strip called a reflectance that allowed each photo to be properly calibrated, ensuring that the gray on a woodpecker or horned lark’s belly was the result of smoke and not a shadow. Once the data was gathered, it was plotted by location and time frame, revealing the history of America’s air quality with impressive specificity.

The dirtiest birds were dated from the beginning of the 20th century, when industrial air pollution was at its peak. Feathers were cleaner when manufacturing declined during the Great Depression, and were then dirtier again during World War II. Birds after the 1955 Air Pollution Control Act looked cleaner than their predecessors, and those that had lived after 1963’s Clean Air Act were cleaner still. When he birds were laid next to each other, the gradation was obvious enough that my four- and eight-year-old immediately picked up on it. My eight-year-old also commented that the dirtier birds were generally smaller as well. Unfortunately, the effects this soot might have had on the birds (ruling out age or other nutritional differences) wasn’t in the study’s scope.

Bird breathing problems

Other studies, however, have looked at the effects on air pollution on our feathered friends, even before they’re covered in soot. Beyond canaries in coal mines, birds’ health has been found to decline from air pollutants faster than humans, as pollutants often lead to thinner egg shells and lower birth rates. Relative body sizes probably play a role, but scientists suspect that bird respiration also contributes to their sensitivity to particulate in the air. While humans breath in and out in two distinct steps, birds breath in a more continuous cycle, essentially inhaling and exhaling in one step. This allows them to fuel the metabolism needed for high-energy tasks like flying without pumping their lungs as a ridiculous rate. It unfortunately also means that they’re more efficient at sucking in soot and other toxins that can cause health problems. So if the birds are suffering in an area, there’s a chance that human health is being attacked as well. Or to put it in a more positive light, you can breath easy if your avian neighbors are clean and in good health.

Source: Sooty Feathers Tell the History of Pollution in American Cities by Alex Furuya, Audubon

On October 17th, 2017 we learned about

Optimistic findings about preventing fires by reducing the amount of flammable fuel in forests

With yet another wildfire filling our skies with smoke, it’s starting to feel like California will never stop burning. The state experienced an unusually rainy winter that thankfully helped fend off a multi-year drought, spurring new plant growth at the same time. Unfortunately, all that vegetation was dried out in record-setting summer heat. From that perspective these fires feel somewhat inevitable, since we can’t stop the rain and many people in power seem intent on avoiding doing much to curb climate emissions that help make more extreme temperatures. However, there’s still opportunities to reduce our fire risks by thinning out the forests themselves, either mechanically or with controlled burns. These aren’t easy tasks to take on, but studies suggest that strategic thinning may reduce some of the costs and logistics associated with wildfire prevention.

For millions of years, forests have occasionally caught fire. In this time, they’ve adapted to make the most of blazes naturally caused by things like lightning strikes, in some cases even evolving pine cones that only open in a fire’s extreme heat. Humans have thrown this balancing act off a bit though, as we both help start fires more often with sparking cars, campfires and cigarettes, but also rush to put those fires out as soon as possible. The result is that forests are now denser than before, not just with living plants but also dry, dead branches, pine needles and more. This means that when a fire does start up, it’s got a lot more fuel to burn, and can get out of control much more quickly.

Small burns aren’t bad

A controlled burn certainly works, because it’s intended to be a safer version of a good lightning strike. Burning a small area ideally clears out dry tinder, but can then be contained before it becomes a problem. Detractors to this method have worried about the fires getting out of control, but also about unintended damage to the environment. To see if prescribed burns were harming plants or animals, the U.S. Forest Service and six universities embarked on detailed studies of the flames’ effects on the affected environment. While there’s obviously smoke and soot after a burn, a smaller fire caused no measurable harm. If anything, plant diversity increased and trees seemed more resilient to things like bark beetles after a small fire. This makes sense, because the more frequent fires of the past would have been smaller on average, and thus something these ecosystems have been able to adapt to.

Mechanical thinning, for less money

Mechanical thinning doesn’t risk running out of control like a fire, and aside from some diesel exhaust, shouldn’t introduce widespread threats to the environment. Instead, detractors bring up the prices and logistics of sending in personnel to clear brush and remove trees, as it can become a huge task in a large forest. Real world experiments were, appropriately, cost prohibitive, so biologists from the University of New Mexico ran simulations of two approaches to mechanical thinning. One option tested the effectiveness thinning vast ranges of land, while the other looked at scenarios where only areas that were considered to be higher risk were dealt with. With all other things being equal, both strategies reduced the severity of simulated fires by as much as 60 percent. This may sound inconclusive until you compare the difficulty of either approach, and realize that the much simpler, cheaper option of thinning only high-risk areas of a forest offers the same benefits for a much smaller price. This means that well-planned mechanical thinning may be more affordable than people previously understood.

If these last two weeks are anything to go by, it looks like we’ll unfortunately have ample opportunities to put these prevention methods to work in the coming years.

Source: Fighting Fires Before They Spark, Scienmag

On October 16th, 2017 we learned about

Currency made from fruit bat teeth offers an opportunity for conservation

How much is a tooth worth? It probably depends on who you ask. A tooth that needs saving at the dentist can get pretty pricey, while a baby tooth that falls out might net around a dollar from the tooth fairy. For mammals like giant fruit bats living in the Solomon Islands, a mouth full of teeth may cost them their lives. Traditional practices on various islands use bat teeth as a form of currency, primarily for ceremonial events like weddings. This, along with the large bats’ meat, has led to increased hunting which is now threatening the safety of various bat species. The good news is that the demand for bat teeth may also turn out to be a way to help keep these same species alive.

Hunting bats for protein and profit

As their name implies, giant fruit bats eat fruit and are big. The Pacific flying fox (Pteropus tonganus), for example, can have a three-foot wingspan while weighing a under two pounds. That may be smaller than your average chicken, but it’s big enough to make these bats a target for islanders looking for scarce sources of protein. It also means that the bats grow teeth large enough to trade and even drill holes in for use in jewelry. While P. tonganus aren’t technically endangered yet, they’re one of many species of bat that are hunted on the Solomon Islands without much care for population management or conservation.

Dietary needs are of course hard to ignore, but trading in teeth has certainly raised a few eyebrows throughout history. Solomon Islanders have been using teeth as currency for centuries, with the practice temporarily dropping off in the 19th century, around the arrival of Christian missionaries. The teeth haven’t only come from bats either, as dolphins have also been hunted for their teeth and meat in a similar manner to the bats. These practices saw a revival around 1948, and while younger islanders feel like these traditions are once again on the decline, they’re still significant enough to make an impact on local ecology. Since these bats are key seed dispersers for the islands, any shift in their populations can spell trouble for the plants, and other animals, that depend on them.

Using culture to motivate conservation

Conservationists focusing on fruit bats suggest that the continuing use of teeth may actually be an opportunity. The fruit bats need better protections from hunting, but also from indirect threats like habitat loss where their deaths are simply an unfortunate byproduct of other goals. However, if the bats’ teeth retain their cultural value, than the bats’ lives will too. The hope is that educating people about the bats’ vulnerability will inspire people to protect them as part of preserving their people’s traditions. Banning hunting outright might help in the short term, but it probably won’t make people feel invested in the bats’ continued success on the islands either, exposing them to further habitat degradation. Promoting teeth as tender as a way to save bat lives may seem counterintuitive, but it’s not a terribly far-fetched idea. Other animals, from sharks to pigs, may also stand a better chance at survival if humans maintain our reason to kill some (but not all) of them.

Source: How to save giant tropical fruit bats: Work with local hunters who use bat teeth as money

On October 9th, 2017 we learned about

White-tailed deer’s dietary preferences inadvertently encourage invasive plant species

White-tailed deer are picky eaters, which poses bigger problems than your usual worries about dietary health. The North American ruminants now live in such dense populations that they make a big impact on whatever plants they choose to eat. Those preferences do shift seasonally, but with millions of deer now living in the United States, that basically means that almost every plant gets a turn to be over-foraged. Experiments have found a key exception to this pattern though, and it’s one conservationists wish the deer didn’t make.

Making space for the wrong species

White-tailed deer (Odocoileus virginianus) have long been known to devour whatever they can reach, but ecologists noticed a possible preference for native species of plants. To test just how choosy deer were, 23 plots of land in various white-tail habitats were fenced off so that the plants living there could be measured and compared. Some plots allowed deer to enter and eat, while others kept the deer out. Scientists were then able to quantify just how much of an impact the deer made on each plant species in a plot, revealing which plants they preferred and which they passed over.

Somewhat unsurprisingly, the deer liked what their ancestors liked. Probably thanks to a genetic predisposition for certain plants that were safe and healthy to eat, the deer ate more native plants than species that were imported or invasive. Importantly, this didn’t change the overall amount of plant growth in a plot, just the composition of those plants. So while a plot may have started out with 50 percent native plants and 50 percent invasive plants, the deer were essentially clearing out the native plants allowing the invasive species to claim the rest of the space. This isn’t just a problem for the native plant species, since the deer were inadvertently promoting the spread of plants that they don’t want to eat, possibly upending their dietary preferences in the future.

Population problems

While the white-tailed deer seem to be making bad situations worse, it’s not entirely their fault. Invasive garlic mustard (Alliaria petiolata), for example, was imported to North America by people as an herb in cooking, but now dominates eastern forests without many natural predators. The deer themselves followed a similar pattern. While they were once hunted to dangerously low levels, conservation laws have helped white-tailed deer populations rebound in the 20th century. However, the deer’s predators like wolves and bears haven’t been so lucky, leaving the deer to multiply unchecked. People now hunt and try to curb deer populations to a degree, but we’re not quite as good at managing their numbers as balanced food-web would be. Since the deer are on course to eat their favorite foods out from under themselves, it appears that the deer aren’t good at managing their populations either.

Source: Deer prefer native plants leaving lasting damage on forests by Lindsey Hadlock, Cornell University Media Relations

On October 4th, 2017 we learned about

Detailed data helps curtail conflict between forest and owl conservation

The forests of Northern California have presented a puzzle for conservationists. On one hand, there was a need to protect the dwindling spotted owl (Strix occidentalis) population, making sure they had enough trees in which to build their nests and lay their eggs. On the other hand, dry conditions from long-term droughts posed a large fire hazard for both the forest and human developments. To reduce the risk of large-scale fires, there was a push to thin forests by culling smaller trees, but this seemed to then threaten the owls’ nests. Fortunately, actual measurements were made, revealing that this presumed conflict wasn’t such of a problem after all.

Mapping more of the forest

This isn’t to say that people were completely inventing the idea that owls might be living in the same trees that were being targeted for clearing. The long-standing practice has been to survey sections of forests, usually less than an acre in size, then extrapolate that data to build an estimate for the rest of the woods. This limited survey was done for practical purposes, as budgeting more comprehensive studies of 1.2 million acres of Sierra Nevada forests was simply unavailable.

Fortunately, new tools are making more complete surveys easier. Researchers from the University of California, Davis, the USDA Forest Service Pacific Southwest Research Station and the University of Washington teamed up to improve our understanding where spotted owls want to live, and the size and shape of the forest overall. They collected data from past studies about where the owls are known to live, then took new measurements of those locations with LiDAR, which is essentially a form of sonar with lasers instead of sound. From a plane flying over the parks, 3D representations of each tree heights and density could be measured and compared with other data. Comparing these measurements of the trees against owl locations revealed an exciting pattern in which trees the owls actually frequented.

Spotted owls’ narrow nesting range

As it turns out, the owls don’t really care for the shorter trees that were marked for fire prevention. They’ll sometimes roost in the shorter trees that make up the forest’s understory, but they want a tall tree when it’s time build a nest. The spotted owls were actually rather picky, limiting their nesting to areas with trees that were at least 105 feet tall, but really preferring those that were at least 157 feet tall. Any place that didn’t reach over 52 feet was avoided altogether, which is great news for people concerned with fire safety.

This doesn’t mean that every shorter tree can be cleared out of the forest, but it does provide a clear path forward for forest and wildlife managers. Instead needing to make unfortunate decisions about where our priorities lie, it seems that simply getting a more detailed understanding of the owl’s ecology will allow us to have our birds and fire safety too.

Source: A Win-Win for Spotted Owls and Forest Management by Kat Kerlin, UC Davis News

On October 2nd, 2017 we learned about

Figuring out why so much of our food ends up tossed in the trash

There are times when my kids seem to be the incarnation of America’s food waste problem. Lunchboxes come home with untouched fruit because it “had a dark spot.” Second helpings of dinner are abandoned on plates after only one or two bites. Vegetables are rejected on sight. It’s a frustrating dynamic, but interesting in how well it matches what many of us do all the time, even if we’re not always willing to admit it to ourselves. Still, with 80 billion pounds of food being tossed out each year, it seems worth taking another look at what we’re dumping in the trash.

Food that’s old or unattractive

One weird twist about my kids’ discarded food is that, unlike 87 percent of us who think they don’t throw out too much, my kids don’t seem to really notice what food goes in the trash. It’s possible that they’re more concerned that they’re not being asked to eat that last veggie, and so the trashcan is their friend in mealtime negotiations. Most adults don’t seem to be throwing out uneaten portions of food they just don’t like, and are instead motivated by concerns about freshness, expiration dates, and possible contamination. Researchers suspect that not all of these concerns are well informed, as things like expiration dates are often misunderstood to be more definitive and accurate than they actually are, meaning many edible items are being tossed out when they shouldn’t be.

Emptying out our refrigerators and pitching our leftovers is really only part of the problem. Huge amounts of food, particularly produce, is rejected before my kids even have a chance to turn their noses up at it. Because people want visually appealing produce, any apple or orange with a blemish is unlikely to sell. In many cases, grocery stores cut consumers out of the equation, rejecting unsightly produce as it’s delivered, even if it means sending a truckload of food back to the farmer. This has pushed farmers to worry about appearances before even stocking their trucks, ploughing veggies into the soil, feeding imperfect watermelons to cows, or dumping precut orange wedges into the landfill.

Small solutions for squishy snacks

Throwing out edible food is provoking a surprising variety of responses. Some people are suspicious grocery stores enjoy extra profits from people rebuying the food they threw out the week before on a regular basis. Others are looking to reclaim and redistribute “ugly” food, either for mainstream consumers or to help feed people who otherwise lack the resources to get any form of produce. Efforts are being made to raise permanently prettier food, such as apples that don’t brown when you cut them up, or baby carrots that remove blemishes consumers would rather not see. In your own kitchen, you can put some of that squishier produce to work in recipes designed for foods slightly past their prime.

When is fruit too far gone?

To be fair, there are times where food shouldn’t be eaten. Unlike the last few bites of my son’s macaroni, it doesn’t make sense for anyone to eat food that is legitimately contaminated. To better find the line between a harmlessly bruised apple and one carrying pathogens, look at the skin around the brown patch. If it’s intact, you’re probably fine. If there’s a break in the skin, and especially if fluid seems to be seeping out, you may have more of a problem. Stems also act as entry points for pathogens, so give them a check too. While there’s a lot of emphasis on looks in all this, smell your food- evolution has made your nose pretty adept at noting when a food smells wrong. Finally, consider the structure of the produce. Bacteria and molds will spread faster through something soft like bananas, but a bell pepper may be salvageable if you cut off the damaged area.

Food-borne illness isn’t something to needlessly risk, so don’t try to be a hero about truly inedible food. Just keep track of what you’re throwing out, and maybe buy better portions to fit your diet so things have less time to rot in the first place.

Source: Food for Thought: Americans Just Can't Stop Throwing Out Food by Sara G. Miller, Live Science

On October 1st, 2017 we learned about

2011’s tsunami sent species across the Pacific in protective plastics and polystyrenes

Why would a fish need a boat? To travel the ocean, of course. It may seem slightly counterintuitive that creatures that live in the ocean might need some kind of flotation device to travel said ocean, but it’s a scenario that’s been playing out for the last six years across the Pacific. Boats, floats, logs and other debris that was swept out to see in the 2011 tsunami off the coast of Japan have been slowly arriving on foreign shores, complete with passengers ranging from shipworms to Japanese barred knifejaw fish (Oplegnathus fasciatus). It’s an unprecedented event, as these creatures are traveling farther, and in greater numbers, than ever before. This uncertainty has biologists worried, as many of these new species may decide to take up residence, rather than simply stop by for a visit.

Durable debris

The fact that the 2011 tsunami pulled debris out into the Pacific ocean is no surprise. Tsunamis, hurricanes and even major storms have long been known to occasionally trap organisms on floating debris before sending them on long journeys. Historically, these unintentional sailors have been stuck on natural materials that would rot or be consumed by things like shipworms along the way, limiting the distance any creature could successfully travel. Of course, we also know that creatures have survived such voyages in the past, often with important repercussions.

The current batch of travelers is experiencing something that humans have known for some time. Thanks to technological developments, the world is effectively getting smaller. Whereas coastal crustaceans, fish and sea stars are generally fenced in to their local habitats by differences in water temperature, salinity, predators and of course, personal mobility, debris made from durable, synthetic materials made long-distance travel possible for the first time. Fiberglass boat hulls filled with water acted like protective shells around fish before arriving on the Washington coast. Polystyrene floats carried oysters to California. The arrivals are slowing down finally, but at least 634 objects have survived the trip, with about 65 percent of those carrying potentially invasive species.

New, unexpected neighbors

With nearly 300 species having arrived on the shore from Alaska to California, there’s a lot of worry about how well they’ll “fit in.” Some, like the Northern Pacific sea star (Asterias amurensis) is already known as an invasive species in other parts of the world. Others raise concerns because they’ve already demonstrated their survivability in making the trip, such as the Bryozoan larvae that only live for a week, and thus must represent many generations of successful reproduction in foreign waters. With the amount of variety that has been found, researchers worry that there’s even more that we’re missing, and that we may soon see dramatic conflicts in shoreline ecosystems. Even if none of these organisms don’t disrupt ecologies now, the next tsunami is sure to send another wave (ahem) of refugees the ever increasing supply of plastic, foam and fiberglass objects being dumped in the oceans.

Not every arrival is starting from scratch though. The slipper snail (Crepidula onyx) was originally native to the eastern shores of the Pacific before it was artificially transported to the coast of Japan. Having had a stint there as an invasive species, it seems that a few individuals have returned to their homeland, hopefully without making too much more trouble for the locals.

Source: Japanese coastal species rode tsunami debris to the US by John Timmer, Ars Technica

On September 24th, 2017 we learned about

Tool-wielding monkeys are reshaping their local supplies of shellfish

A macaque monkey, like a human, doesn’t have the anatomy to pry open an oyster on its own. As nimble as our primate fingers are, they’re just not suited to opening these shellfish… unless they’re being used to hold a tool. Humans have created a lot of tools for this task, but macaque monkeys on NomSao and Koram, islands off the coast of Thailand, have shown you only need some rocks and know-how. Scientists following these monkeys have found that they’ve become quite adept at cracking open a variety of shellfish, with a single monkey consuming as many as 40 pieces of seafood a day. As humans (sort of?) know, that efficiency comes with a cost though, leaving the monkeys at risk for eating their favorite foods into oblivion.

Tradition of tool-use

Long-tailed macaque monkeys (Macaca fascicularis) are one of the few species of primates that use stone tools to help them work. While many animals use twigs and plants to help obtain resources, stone tools are of particular interest because of their durability, and their the parallels to early hominid tool creation. We’ve found examples of stone tools from generations ago, and eyewitness reports assert that these Thai monkeys have been using tools for at least 120 years. Researchers wondered if that was enough time for the monkeys to reshape their ecosystems like humans do, if on a smaller scale.

Obviously, researchers couldn’t go back in time to see the first day a monkey wielded a stone to crack open an oyster. Instead, they followed a larger population of monkeys on the island of Koram, and a smaller group living on NomSao. Both groups of monkeys used rocks to break open their shellfish, so the key point of comparison was population size. If tool-using monkeys were making an impact on their favorite foods, that impact would be magnified by more monkeys.

Larger impact of shrinking shellfish

This hypothesis proved true. NomSao had larger shellfish populations than the monkey-dense island of Koram. What’s more, the oysters, snails and other morsels were generally smaller on Koram, which is likely an effect of the monkeys’ targeted predation. If a smaller oyster is less likely to be munched by a monkey, then smaller oysters are more likely to survive and reproduce, eventually reducing the average size of these animals.

The monkeys may end up dealing with reductions of their own. If the shellfish are no longer abundant or big enough to be worth feeding on, the monkeys may have to find food elsewhere, abandoning their seafood diets. Researchers aren’t worried that the macaques will starve, but are curious about their tool use. Without reinforcement, or a way to preserve their techniques in writing like humans do, there’s a chance the monkeys will essentially forget their Stone Age advancements. That wouldn’t mean that tastier shellfish might rekindle the use of rocks in the future though- a separate study watching macaques found that they developed techniques to crack open oil palm nuts in less than a generation, as the nuts have only been in their area for 13 years.


My four-year-old asked: If the monkeys can’t eat oysters, will they eat bananas?

They might. Long-tailed macaques will eat just about anything they can, with fruits and seeds making the bulk of their diets. Thailand has a few different types of bananas, and while they don’t necessarily look like what turns up in western grocery stores, the monkeys probably still enjoy them from time to time.

Source: Tool-wielding monkeys push local shellfish to edge of extinction by Aylin Woodward, New Scientist

On September 12th, 2017 we learned about

Steephead parrotfish plan, preserve and protect their favorite plots of algae

One of the functions of predators in an ecosystem is to keep herbivores from eating themselves out of house and home. For example, the reintroduction of wolves to Yellowstone National Park in 1995 has helped a variety of species, including the elk the wolves prey on, as they no longer over-forage on stands of willow trees. Not every creature needs to be policed by a predator though, as scientists tracking steephead parrotfish have found that the herbivores do a good job of regulating themselves. Even without fear of being eaten by larger hunters, these fish are keeping themselves fed and promoting balance in their ecosystem at the same time.

Resource rotation

Steephead parrotfish (Chlorurus microrhinos) living near the Palmyra atoll love eating the thick algae that grows in the area. This appreciation seems to extend learning the algae’s life cycle, as the fish will feed on patches of the thick sheets of plant life for a period of time, but move on before completely wiping it out. They then feed on a different patch of algae, moving when that area is thinned out. The parrotfish will continue this cycle, only feeding on their first plot of algae once it’s had sufficient time to recover. They seem to realize that if handled properly, the algae are a renewable resource that’s worth preserving, and protecting.

Parrotfish wouldn’t move on too far from a patch of algae after eating, because they also wanted to guard it from their peers. Big hunks of turf algae would especially attract the efforts of large, male fish in particular. The fish would chase away potential rivals, ensuring their plot of algae-covered coral would be ready to eat when they were ready. In contrast, smaller male and female fish were seen more often in areas where the algae coverage was a bit more dispersed, and presumably harder to stake out as a single location.

Picking off unwanted plants

These carefully tended patches of algae matter to more than just the hungry and jealous parrotfish. Algae growing on coral can be harmful, to the point of being lethal to coral larvae. By scraping the algae off rocks and coral, the parrotfish give the surrounding ecosystem a boost. Larval coral in particular have been found to take advantage of the freshly scraped areas to get a foothold, hopefully becoming robust enough to survive the eventual return of the algae. Since coral supports so many forms of life, this constant, if rough, pruning of algae growth is regarded as a net win for reef ecosystems.

Source: Farming Fish by Julie Cohen, The Current

On September 11th, 2017 we learned about

Smooth surfaces are essentially invisible to bats’ ultrasonic echolocation

My third-grader still recalls, with an odd amount of fondness, the last time she walked into a glass door. The smooth, clear glass had no hints of grime or glare to describe it’s surface, and she smacked into it at full speed. Birds famously do this too, but it’s been a little more puzzling why bats have the same problem with glass-covered buildings. When the bats are out at night, windows usually look like dark monoliths more than clear openings, but that only helps if you navigate primarily with your eyes. If you find your way around the world with echolocation, all that glass becomes invisible in a whole new way.

An absence of echoes

Similarly to the way your eyes detect light bouncing off of the objects around you to see, bats listen for sounds to understand where they are and what’s near by. Rather than relying on other sources of sound, they squeak at ultra-high frequencies humans can’t hear, and as those sound waves reflect off of objects, the bat can gauge their timing and amplitude to know where the next rock, tree or insect is located. When sound doesn’t reflect back, it’s usually a fair assumption that there’s open space in that direction. Unless of course there’s actually a building there.

A series of experiments looked at how greater mouse-eared bats (Myotis myotis) maneuvered in the vicinity of a smooth piece of flat metal, set up as an analog for glass plate windows. The metal, and glass, can be so smooth that incoming sound waves don’t scatter back to the bat— they simply reflect off at a complementary angle like light from a laser pointer on a mirror. While bats aren’t blind, the lack of feedback from their primary sensory system leads them to fly at full speed into these objects, often leading to injuries or even death.

Horizontal surfaces seen as still water

The one exception to this is when the metal plates were placed on the ground, as their context suddenly changed how bats interpreted the apparent void in front of them. While most objects in a bats natural habitat are rough, bumpy or at least uneven enough to reflect sound, still water can apparently be smooth enough to bounce no sound back to the bat’s ears. When metal plates were placed horizontally on the ground, bats would try to skim their surface for a drink, even from a young age that couldn’t have been taught this kind of behavior. This misunderstanding is what got researchers looking at how smooth surfaces confuse bats in general, hopefully getting us closer to a strategy to prevent some of these collisions.

Broadcasting building locations

One possible course of action would be to build acoustic deterrents on buildings near large bat colonies. Since bats operate in ultrasonic frequencies invisible to our ears, speakers could emit sounds from buildings to essentially broadcast their locations to the flying insectivores. The smooth, vertical surfaces would then be revealed, or at least advertised as a place you shouldn’t try to fly through when chasing down bugs.

Source: Bats crash into windows because of a glitch with their ‘sonar’ by Michael Le Page, New Scientist