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Researchers Explain How They Tracked Migrating Birds

Arrival times of migratory song birds is really important for their reproductive success

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This June 18, 2016, photo provided by the U.S. Geological Survey shows a Yellow Warbler in Nome, Alaska
This June 18, 2016, photo provided by the U.S. Geological Survey shows a Yellow Warbler in Nome, Alaska, VOA
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Tracking wildlife migration has been historically difficult in the rugged terrain of Alaska. Researchers primarily rely on either surveys or GPS tracking to understand bird migration patterns. Both methods are expensive, either in terms of time or money. And the trackers are often too large or heavy.

One way to sidestep these common issues is to record audio from frequently used nesting grounds. Using birdsong allows researchers to unobtrusively study the animals, although there’s a downside. Each day produces a flood of audio recordings from multiple microphones placed around nesting grounds. It takes trained listeners endless hours to search the noisy soundscape for birdsong.

In a recently published paper in the journal Science Advances, U.S. researchers explain how they got around these tracking troubles. Columbia University ecologist Ruth Oliver and her fellow collaborators replaced the human ears with machine learning algorithms to listen to birdsong.

Costly proposition

Oliver told VOA News, “Arrival times of migratory song birds is really important for their reproductive success. And obviously sending people to the Arctic to do field work is very expensive and takes a lot of time” — hence, the scientists’ interest in creating an automated method for tracking bird species.

Oliver and her colleagues focused on migratory songbirds who fly to northern Alaska during their mating season. These birds tend to chirp more frequently as soon as they reach the breeding grounds to attract a mate. Spring is short in Alaska and the birds must breed and hatch their clutch before winter.

This July 16, 2016, photo provided by the U.S. Geological Survey shows an Arctic Warbler in Nome, Alaska
This July 16, 2016, photo provided by the U.S. Geological Survey shows an Arctic Warbler in Nome, Alaska, VOA

The team of researchers recorded the springtime soundscape of northern Alaska for five sequential years. They placed microphones at four sites in the foothills of the Brooks Range, which recorded 1,200 audio hours.

However, Oliver admitted the recordings weren’t always perfect. “There’s a lot of other noise in these recordings” Oliver said. “Even in May in northern Alaska there’s lots of wind, lots of rain, and all of that is confounding when you’re listening to birds.”

The scientists fed hours of audio into two types of machine learning algorithms — one that used human expertise to help train it and one that relied solely on the collected audio. Both algorithms were based on the same model that’s used by applications like Siri and Alexa.

Oliver told VOA that in creating the human-supervised algorithm, she “wrote a little program to randomly sample about 1 percent of the data set” and then listened to 4-second clips. She scored these clips as either containing or not containing songbird vocalizations and then fed this information into the program.

Both algorithms were fairly accurate at estimating when the avian commuters arrived in the foothills. The models showed the importance of snowmelt for the arrival of the traveling birds. The human-trained model was slightly better at recognizing the relationship between weather conditions and bird calls, although neither model specifically tracked individual species.

This technique has great potential according to Emily Jo Williams, vice president of migratory birds and habitat at the American Bird Conservancy, “This kind of technique that allows you to survey populations in those remote areas is really exciting and could allow us to even discover new places where protection and conservation efforts are needed,” she said.

This study looked at nesting grounds near the Alaskan Arctic Refuge, which is a summer home for birds from nearly every continent. For example, the Northern Wheatear travels approximately 21,000 kilometers (13,000 miles) from Africa to summer in the refuge.

 This July 7, 2016, photo provided by the U.S. Geological Survey shows a Bluethroat in Nome, Alaska
This July 7, 2016, photo provided by the U.S. Geological Survey shows a Bluethroat in Nome, Alaska, VOA

Climate change

Williams told VOA, “We know from some research that some birds’ ranges have actually changed, and they’ve moved in response to what we think is a warming climate.” She went on to explain that “the timing of that migration has evolved over eons, and in large part it’s relative to what food sources are available over a particular time, what weather patterns are or aren’t favorable. So you could end up with bird migration out of sync with insect hatches or the phenology of plants that birds have a relationship to.”

Also read: Study Shows That The First Tree-Dwelling Birds Went Extinct With Dinosaurs

Tools like the algorithm created in this study could be used to track how migratory patterns of many species may shift in response to climate change. Using machine learning is a new way to follow these shifting patterns in birds, insects and other animals. (VOA)

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Next On Its Way To Extinction: Mountain Birds

Birds adapted to live within narrow temperature bands — in regions without wide seasonal variations — may be particularly vulnerable to climate change

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Handout picture released in Lima by the Peruvian Commission for the Promotion of Export and Tourism (PROMPERU), showing a hummingbird spotted during the Birding Rally Challenge taking place in the northern Peruvian mountain jungle close to the city of Tarapoto on June 12, 2013. VOA

A meticulous re-creation of a three-decade-old study of birds on a mountainside in Peru has given scientists a rare chance to prove how the changing climate is pushing species out of the places they are best adapted to.

Surveys of more than 400 species of birds in 1985 and then in 2017 have found that populations of almost all had declined, as many as eight had disappeared completely, and nearly all had moved to higher elevations in what scientists call “an escalator to extinction.”

“Once you move up as far as you can go, there’s nowhere else left,” said John W. Fitzpatrick, a study author and director of the Cornell Laboratory of Ornithology. “On this particular mountain, some ridgetop bird populations were literally wiped out.”

It’s not certain whether the birds shifted ranges because of temperature changes, or indirect impacts, such as shifts in the ranges of insects or seeds that they feed on.

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A gull flies with the “Dents du Midi” multi-summited mountain as background on July 3, 2016 in Montreux, Switzerland. VOA

These findings, published Monday in the Proceedings of the National Academy of Sciences, confirm what biologists had long suspected, but had few opportunities to confirm. The existence of a 1985 survey of birds on the same mountain gave scientists a rare and useful baseline.

Past research has documented habitats of birds and other species moving up in elevation or latitude in response to warming temperatures. But Mark Urban, director of the Center of Biological Risk at the University of Connecticut, who was not involved in the study said it was the first to prove what climate change models predicted: that rising temperatures will lead to local extinctions.

“A study like this where you have historical data you can go back to and compare is very rare,” said Urban. “As long as the species can disperse, you will see species marching up the mountain, until that escalator becomes a stairway to heaven.”

In 1985, Fitzpatrick established a basecamp alongside a river running down a mountain slope in southeastern Peru, aiming to catalog the habitat ranges of tropical bird species that lived there. His team spent several weeks trekking up and down the Cerro de Pantiacolla, using fine nets called mist nets to catch and release birds, and keeping detailed journals of birds they caught, spotted or heard chirping in the forests.

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A bird flies past the Humayun’s Tomb shrouded in smog in New Delhi, India. VOA

Two years ago, Fitzpatrick passed his journals, photos and other records to Benjamin Freeman, a postdoctoral fellow at the Biodiversity Research Centre at the University of British Columbia. Freeman, who has been researching tropical birds for more than a decade, set out to recreate the journey in August and September of 2017. Using old photos of mountain views, his team located the same basecamp.

Freeman largely recreated Fitzpatrick’s path and methodology to see what had happened in the intervening years, a period when average mean temperatures on the mountain rose 0.76 degrees Fahrenheit (0.42 degrees Celsius). Because the mountain lies at the edge of a national park, the area hadn’t been disturbed.

In addition to unfurling 40-foot (12-meter) mist nets on the slopes, Freeman’s team placed 20 microphone boxes on the mountain to record the chirps of birds that might not easily be seen.

“We found that the bird communities were moving up the slope to reach the climate conditions to which they were originally adapted,” said Freeman, the lead author of the study. Near the top of the mountain the bird species moved higher by 321 feet (98 meters), on average.

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It’s not certain whether the birds shifted ranges because of temperature changes

“We think temperature is the master-switch in explaining why species live where they do on mountain slopes,” said Freeman. “A huge majority of species in our study were doing the same thing.”

Also Read: 60 Percent Wildlife Lost In Just Four Decades: Report

Birds adapted to live within narrow temperature bands — in regions without wide seasonal variations — may be particularly vulnerable to climate change, Fitzpatrick said.

“We should expect that what’s happening on this mountaintop is happening more generally in the Andes, and other tropical mountain ranges,” he said. (VOA)