Monthly Archives: December 2017

Snowy owl numbers far lower than once thought

Snowy owl migration gives scientists chance to study them
(Tammy Webber 21 Dec 2017)

Scott Judd trained his camera lens on the white dot in the distance. As he moved up the Lake Michigan shoreline, the speck on a breakwater came into view and took his breath away: it was a snowy owl, thousands of miles from its Arctic home.

“It was an amazing sight,” said Judd, a Chicago IT consultant. “It’s almost like they’re from another world. They captivate people in a way that other birds don’t.”

The large white raptors have descended on the Great Lakes region and northeastern U.S. in huge numbers in recent weeks, hanging out at airports, in farm fields, on light poles and along beaches, to the delight of bird lovers.

But for researchers, this winter’s mass migration of the owls from their breeding grounds above the Arctic Circle is serious business.

It’s a chance to trap and fit some of the visitors with tiny transmitters to help track them around the globe and study a long-misunderstood species whose numbers likely are far fewer than previously thought, researchers say.

“There is still a lot that we don’t know about them … but we aim to answer the questions in the next few years,” said Canadian biologist Jean-Francois Therrien, a senior researcher at Hawk Mountain Sanctuary in Pennsylvania.

The solar-powered transmitters can last for years, collecting information such as latitude, longitude, flight speed and air temperature that is downloaded to a server when the birds fly into range of a cell tower.

The use of transmitters, which intensified during the last North American mass migration in winter 2013-14, already has yielded big surprises.

Instead of 300,000 snowy owls worldwide, as long believed, researchers say the population likely is closer to 30,000 or fewer. The previous estimate was based on how many might be able to breed in a given area.

That calculation was made assuming snowy owls acted like other birds, favoring fixed nesting and wintering sites. But researchers discovered the owls are nomads, often nesting or wintering thousands of miles from previous locations.

The miscalculation doesn’t necessarily mean snowy owls, which can grow to about 2 feet long with 5-foot wingspans, are in decline. Scientists simply don’t know because they never had an accurate starting point.

This month, snowy owls were listed as vulnerable—one step away from endangered—by the International Union for Conservation of Nature. They’re protected in the U.S. under the Migratory Bird Act.

This year’s mass migration is a bit of good news. Researchers once thought these so-called “irruptions” signaled a lack of prey in the Arctic, but now believe the opposite: Breeding owls feed on lemmings, a rodent that lives under Arctic snowpack and whose population surges about every three or four years. More lemmings means the owl population explodes— and that more birds than usual will winter in places people can see them.

 But researchers worry that climate change will affect the owl population because lemmings are exceptionally sensitive to even small temperature changes.

Lemmings “depend on deep, fluffy, thick layers of insulating snow” to breed successfully, said Scott Weidensaul, director at Project SNOWstorm, an owl-tracking group whose volunteers have put transmitters on more than 50 snowy owls in the past four years .

The snowy owl population collapsed in Norway and Sweden in the mid-1990s, all but vanishing there for almost two decades before reappearing at lower numbers, experts said. In Greenland, where the population collapsed in the late 1990s, researchers found a few nests in 2011 and 2012 after six years with no recorded nests, but owls didn’t come back in 2016 or 2017, when lemmings should have been peaking.

The National Oceanic and Atmospheric Administration reported this month that the far northern Arctic is warming twice as fast as the rest of the globe.

But it’s tough to assess lemming population trends in remote areas. Although researchers hope to enlist native villagers to help, it’s mostly up to owls with transmitters for now.

Snowy owls somehow seem to find lemmings even if they are thousands of miles from where their population last peaked, Therrien said.

“They look around the Arctic,” he said. “The movement is amazing to watch on a map: There are no straight lines. They’re zigzagging.”

Norman Smith, a snowy owl expert with Mass Audubon in Massachusetts, said he’s heartened that many independent researchers worldwide joined forces to share information on snowy owls.

“It’s amazing what we’ve learned, but we need a bigger database of birds,” said Smith, who has been trapping owls at Boston’s Logan International Airport for more than 35 years and fits them with a leg band or transmitter before letting them go. He put a satellite tracker on an owl for the first time in 2000, proving that they could make it back to the Arctic.

Last week, Smith released a young female on a barrier beach along the Atlantic Ocean. It flew south, then circled back and flew overhead. As he drove over a bridge to the mainland, the owl was sitting on a post, surveying its new winter home.

Snowy owl migration gives scientists chance to study them

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Social interactions override genetics when birds learn new songs

(Nicholas Weiler, 26 Dec 2017)

New UC San Francisco research finds that although young male songbirds are genetically predisposed to sound like their fathers, enriched early experience with a foster-father can overcome this genetic destiny. This finding has striking implications for our thinking about how experience influences the genetics of complex human traits like learning ability or even psychiatric disease, the authors say.

Neuroscientists like UCSF’s Michael Brainard, Ph.D., have long studied songbirds like the Bengalese finch (Lonchura striata domestica) as a model of how complex behaviors like human language are shaped by early experience. Like human language, a male finch’s unique mating song is learned early in life by listening to and mimicking adult “tutors.” In nature, this is usually the bird’s father, but young birds raised by unrelated adults in the lab will learn to sing their foster-father’s song instead.

Now Brainard’s lab has shown that not all early experiences are equal in their influence over impressionable young birds: exposed only to a computerized “synthetic tutor,” young birds will revert to singing like a biological father they’ve never known or heard. The research—published the week of December 25, 2017 in PNAS—suggests that finch song has a stronger genetic component than had previously been realized, but also that this genetic drive can be suppressed by the right kind of early life experience.

“What we saw is that the genetic contribution to a bird’s song depends on the specifics of that bird’s experience. This is a striking demonstration that heritability for complex behaviors like birdsong is not fixed, as is often assumed, but instead can vary dramatically depending on the experience of an individual,” said Brainard, a professor of physiology and of psychiatry at UCSF, Howard Hughes Medical Institute investigator, and member of the UCSF Weill Institute for Neurosciences.

As noted, researchers have long considered the structure of adult birdsong to be dominated by the influence of whatever song a bird hears as a chick. However, David Mets, Ph.D., a postdoctoral scholar in the Brainard lab and the new paper’s first author, noticed a surprising amount of variation between the songs of individual Bengalese finches in the lab, even when all birds were exposed to the same experimentally controlled tutor song early in life.

To determine whether these differences might be caused by a previously overlooked genetic contribution to the birds’ song, Mets developed a careful set of experiments to control the contribution of genetics and experience. He removed eggs from their nests shortly after they were laid to ensure chicks never heard their fathers’ song, even in the egg. He then exposed the hatchlings only to carefully controlled computer-generated songs, which he varied in tempo in an attempt to influence the tempo of the song the young birds would learn.

To the researchers’ surprise, they found that these birds largely ignored the tempo of the synthetic songs, and developed adult songs with tempos much closer to their fathers’ songs—which they had never heard. The researchers quantified this observation, showing that 55 percent of variability in the experimental birds’ songs could be explained by differences in their fathers’ songs, but only 21 percent was driven by differences in the synthetic song they heard as chicks.

In a second set of experiments, Mets got rid of the synthetic tutor and instead exposed finch chicks—which also had never heard their fathers’ songs—to unrelated live adult males. The researchers were again surprised to discover a complete reversal of the results seen with synthetic tutoring: the live tutor’s song contributed 53 percent to the tempo of the young birds’ adult songs, with differences in their fathers’ songs contributing only 16 percent.

“This was really exciting because it showed that the experience provided by a live tutor can actually reduce the contribution of genetics to complex behavior like birdsong,” Mets said. “We knew before that live tutors helped birds learn better and faster, but we were surprised to find that this experience can actually override the bird’s genetics.”

“We’ve gotten used to the idea that complex traits and behaviors can have a big genetic component,” Brainard added, citing human studies of identical twins separated at birth who nonetheless share surprising similarities in things like their sense of humor, fashion sense, and so on. “But those stories tend to assume that the genetic component is fixed—academic achievement is either 20 percent genetic or 80 percent genetic. We’re showing here that the contribution of genetics is anything but fixed—in the case of academic achievement, the school you go to may well overcome any contribution of genetics.”

The findings raise the possibility that human genetic studies that fail to account for differences in individuals’ experience could be producing misleading conclusions about the genetic contributions to complex behaviors, Brainard said.

The researchers now hope to use the Bengalese finch as a model to explore how genetics and experience interact in the brain to influence complex behaviors like birdsong. “Where in the brain are the father’s genes and early life experience competing for control over song tempo?” Mets asked. “That’s the next really exciting question.”

The results also suggest a broader opportunity to understand the specific features of enriched early experiences that allows them to override genetic predispositions, Brainard said: “This is far into the future, of course, but it highlights the potential of early behavioral intervention to help mitigate negative genetic traits, such as a predisposition to psychiatric disease.”

Birds learn from each other’s ‘disgust,’ enabling insects to evolve bright colors

(University of Cambridge 18 Dev 2017)

Many animals have evolved to stand out. Bright colours are easy to spot, but they warn predators off by signalling toxicity or foul taste.

Yet if every individual predator has to eat colourful prey to learn this unappetising lesson, it’s a puzzle how conspicuous colours had the chance to evolve as a defensive strategy.

Now, a new study using the great tit species as a “model predator” has shown that if one bird observes another being repulsed by a new type of prey, then both birds learn the lesson to stay away.

By filming a great tit having a terrible dining experience with conspicuous prey, then showing it on a television to other tits before tracking their meal selection, researchers found that birds acquired a better idea of which prey to avoid: those that stand out.

The team behind the study, published in the journal Nature Ecology & Evolution, say the ability of great tits to learn bad food choices through observing others is an example of “social transmission.”

The scientists scaled up data from their experiments through mathematical modelling to reveal a tipping point: where social transmission has occurred sufficiently in a predator species for its potential prey to stand a better chance with bright colours over camouflage.

“Our study demonstrates that the social behaviour of predators needs to be considered to understand the evolution of their prey,” said lead author Dr Rose Thorogood, from the University of Cambridge’s Department of Zoology.

“Without social transmission taking place in predator species such as great tits, it becomes extremely difficult for conspicuously coloured prey to outlast and outcompete alternative prey, even if they are distasteful or toxic.

“There is mounting evidence that learning by observing others occurs throughout the animal kingdom. Species ranging from fruit flies to trout can learn about food using social transmission.

“We suspect our findings apply over a wide range of predators and prey. Social information may have evolutionary consequences right across ecological communities.”

Thorogood (also based at the Helsinki Institute of Life Science) and colleagues from the University of Jyväskylä and University of Zurich captured wild great tits in the Finnish winter. At Konnevesi Research Station, they trained the birds to open white paper packages with pieces of almond inside as artificial prey.

The birds were given access to aviaries covered in white paper dotted with small black crosses. These crosses were also marked on some of the paper packages: the camouflaged prey.

One bird was filmed unwrapping a package stamped with a square instead of a cross: the conspicuous prey. As such, its contents were unpalatable — an almond soaked with bitter-tasting fluid.

The bird’s reaction was played on a TV in front of some great tits but not others (a control group). When foraging in the cross-covered aviaries containing both cross and square packages, the birds exposed to the video were quicker to select their first item, and 32% less likely to choose the ‘conspicuous’ square prey.

“Just as we might learn to avoid certain foods by seeing a facial expression of disgust, observing another individual headshake and wipe its beak encouraged the great tits to avoid that type of prey,” said Thorogood.

“By modelling the social spread of information from our experimental data, we worked out that predator avoidance of more vividly conspicuous species would become enough for them to survive, spread, and evolve.”

Great tits — a close relation of North America’s chickadee — make a good study species as they are “generalist insectivores” that forage in flocks, and are known to spread other forms of information through observation.

Famously, species of tit learned how to pierce milk bottle lids and siphon the cream during the middle of last century — a phenomenon that spread rapidly through flocks across the UK.

Something great tits don’t eat, however, is a seven-spotted ladybird. “One of the most common ladybird species is bright red, and goes untouched by great tits. Other insects that are camouflaged, such as the brown larch ladybird or green winter moth caterpillar, are fed on by great tits and their young,” said Thorogood.

“The seven-spotted ladybird is so easy to see that if every predator had to eat one before they discovered its foul taste, it would have struggled to survive and reproduce.

“We think it may be the social information of their unpalatable nature spreading through predator species such as great tits that makes the paradox of conspicuous insects such as seven-spotted ladybirds possible.”

Video: https://www.youtube.com/watch?v=87l0Dyte_nQ

Rooftop wiretap aims to learn what crows gossip about at dusk

(University of Washington 5 Dec 2017)

What are crows saying when their loud cawing fills a dark winter’s evening? Despite the inescapable ruckus, nobody knows for sure. Birds congregate daily before and after sleep, and they make some noise, but what might be happening in those brains is a mystery.

Curious about these raucous exchanges, researchers at the University of Washington Bothell are listening in. They are placing equipment on the roof of their building — a meeting place for some of the thousands of crows that sleep in nearby campus trees — and using a sort of computerized eavesdropping to study the relationship between calls and the birds’ behavior.

“With audio alone, our team is able to localize and record the birds remotely, and in dim light that makes this situation less suitable for video tracking,” said Shima Abadi, an assistant professor at UW Bothell’s School of Science, Technology, Engineering & Mathematics. “It’s still a challenging task, but we can use the audio signals to look for patterns and learn more about what the birds may be communicating.”

Abadi’s background is in ocean acoustics; some of her previous research tracks whales using underwater microphones in the ocean water. For this project she teamed up with a colleague in biology who studies the local crow population with his undergraduate students.

“They’re incredibly raucous, and make this cacophony every night, and people wonder: What are they saying? And that’s a great question to ask on this campus,” said Douglas Wacker, an assistant professor of biology at UW Bothell.

Wacker earned his UW doctorate studying song sparrows. After joining UW Bothell in 2012, it was only natural that he study the roughly 15,000 crows that migrate to the North Creek Wetlands on campus each evening in fall, winter and spring.

People walking through campus can’t fail to hear the not-always-melodious sound of the birds.

“Crows make a variety of different calls, some of which we understand the functions of fairly well, and others not as well,” Wacker said. “Their normal ‘caw’ calls are not necessarily well understood — we don’t know what information they might be conveying.”

He and Abadi have nearby offices. They decided last year to collaborate on an interdisciplinary project that blends his biology background with her acoustics expertise.

While the field site on the roof of the faculty members’ building is convenient, this project poses technical challenges. These crows call in a noisy environment, where it is tricky to separate their vocalizations from different birds and other surrounding sounds. What’s more, crows are intelligent. They will change their behavior if they think humans are watching, or even if unfamiliar equipment is nearby.

That’s why the high-tech approach, worthy of an avian CSI, is needed.

The team of mostly undergraduate students has been perfecting its audio recording technique. They placed four audio recorders in a 10-foot square in a parking lot, and then placed a speaker playing a crow call in one of the quadrants. The recorders have precise time stamps to calculate when the sound waves arrive, and then software compares the times to pinpoint where the sound was generated.

The students figured out a way to focus on the highest-quality audio to triple the accuracy of the source locations. They can now use the recordings to locate the source of the call to within 6-12 inches, or about the size of a bird.

About 50 to 100 crows might assemble in the pre-roost gathering at dusk on the roof of the science building. Their incessant cawing during flight quietens to just the occasional outburst while on the roof. With Abadi’s help, the team is working to develop a user interface and computer techniques that pick out particular calls, so they do not have to manually pick through hours of cawing but can focus on the most interesting events.

Derek Flett, a senior undergraduate student in mechanical engineering, will describe the team’s efforts Dec. 5 at the Acoustical Society of America’s annual meeting in New Orleans.

This winter they plan to use the equipment in the wild — that is, on the roof — to monitor real groups of crows. Eventually they hope to combine the audio surveillance with video, so they could study how birds might react to particular sounds.

They have also begun to test their theories by playing particular calls and then seeing whether the crows react in the predicted manner.

The idea that the calls contain meaning is plausible, Wacker said. The number of caws, or the length of the pauses between caws, could say something about food sources or possible dangers.

“If a bee can do a dance to tell other bees where food is located, then certainly a highly intelligent bird — in a family with other bird species that are capable of insight learning, recognizing themselves in a mirror, recognizing faces and passing that information on to subsequent generations — could be capable of communicating complex information,” Wacker said.

The other co-author on the work being presented in December is Virdie Guy, an undergraduate in mechanical engineering. The research was funded by a UW Royalty Research Fund.

Complex, old-growth forests may protect some bird species in a warming climate

(Oregon State University 15 Dec 2017;Photo:Hankyu Kim)

Old forests that contain large trees and a diversity of tree sizes and species may offer refuge to some types of birds facing threats in a warming climate, scientists have found.

In a paper published in Diversity and Distributions, a professional journal, researchers in the College of Forestry at Oregon State University reported that the more sensitive a bird species is to rising temperatures during the breeding season, the more likely it is to be affected by being near old-growth forest.

Researchers studied 13 bird species that have been tracked annually in the U.S. Geological Survey’s annual Breeding Bird Survey, one of the most comprehensive efforts of its kind in North America. Only two — the Wilson’s warbler and hermit warbler — showed negative effects from rising temperatures over the past 30 years, but actual counts of both species show that their populations are stable or increasing in areas that contain high proportions of old-growth forest.

A team led by Matthew Betts, professor in the College of Forestry, reached their conclusions by analyzing data for bird populations, forest structure and climate across northwestern North America. The researchers used satellite imagery to determine the amount of old-growth forest within about 450 yards of each 25-mile-long bird survey route.

The findings provide an additional reason for old-growth forest conservation, said Betts. “Managers hoping to combat the effects of climate change on species’ populations may now have an additional tool — maintaining and restoring old-growth forest.” He noted that this is important because management recommendations from biodiversity and climate studies have traditionally been sparse. Such studies have tended to focus on moving species to cooler climates or simply reducing carbon emissions.

Wilson’s warbler winters in Mexico and breeds during the late spring and early summer along the West Coast and across northern North America from Alaska to New England and the Canadian Maritimes. Although it occurs in early-stage as well as mature forests, it is declining at a rate of about 2 percent per year in the Pacific Northwest.

The hermit warbler also winters in Mexico but breeds exclusively along the West Coast as far north as Washington. Its populations are relatively stable but declining in landscapes with low amounts of old-growth forest.

Additional research will be needed to identify the specific features of mature forests that buffer the effects of warming temperatures on birds. One possibility, the researchers said, is that the large trees themselves function as “heat sinks” during warm periods and thus moderate temperatures. Multiple canopy layers may also provide climate buffering effects.

For the love of birds

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From the glorious crested guinea fowl to the adulterous African jacana to vultures that can pick a zebra carcass clean in 30 minutes, Washington Wachira wants us all to get to know the marvelous species of birds that share the planet with us. If you’re not already a fan of earth’s feathermakers — or concerned about their conservation — you will be after you watch this delightful talk.