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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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Thailand: Elephants Aid in Spreading Fruit Seeds

Based on the diets and habits of mammals, scientists found that elephants are the best allies for the Thai Annonaceae tree to spread its seeds.

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Asian Elephants are the major seed dispersers for the p. macrocarpa. Pixabay

Massive fruit trees in the Thailand evergreen forest need Elephants to help spread their seeds, according to a new study.

Based on the diets and habits of mammals, scientists found that elephants are the best allies for the Thai Annonaceae tree to spread its seeds.

In the diverse environment of Khao Yai National Park, there is a complex set of relationships between the plants and animals. Not every species of fruiting tree is an attractive meal to all herbivores. A team of researchers, led by Kim McConkey from the University of Nottingham, set out to study one particular tree, the Platymitra macrocarpa from the family of custard apple trees.

The p. macrocarpa produces 3-to-5-inch fruit that are ripe from May through August. McConkey tracked how often animals visited the trees and ate the fruit, including elephants, bears, monkeys, gibbons and Sambar deer. They measured the animals’ fruit consumption as well as the ensuing seed dispersal and seed viability.

Researchers found the seeds in the dung of some species while others like the Sambar deer regurgitated the large seeds. When asked about tracking animal poop, McConkey admitted, “I’ve got two boys so they just love what I do.”

As expected, the Asian elephants were the major seed dispersers for the p. macrocarpa. Elephants aren’t often seen in the area of the trees McConkey studied, but as she told VOA, “I thought if I’m going to see them feed on any fruit, it’s going to be this one.” Her hunch was borne out in the data, with elephants consuming only 3 percent of the fruit but producing 37 percent of the viable seedlings.

Elephants
The p. macrocarpa produces 3-to-5-inch fruit that are ripe from May through August. VOA

These findings regarding the Asian elephants point to the important role they play in the ecosystem. Jedediah Brodie, chair of conservation in the Wildlife Biology Program at the University of Montana, told VOA that “overhunting in the tropics often drives large animals locally extinct but leaves smaller species like rodents. And this study shows that those smaller animals just are not able to replicate the ecological role of the larger species.”

When looking at the performance of other species, the researchers were surprised by how effective Sambar deer were at dispersing seeds. “Sambar deer generally have quite a bad rap in these forests,” McConkey said. “People think they’re seed predators, but it turns out they actually do disperse a lot of seeds.” While the Sambar deer weren’t quite as effective seed dispersers as gibbons (21 percent), they still produced a respectable 17 percent.

Bruchid beetles were the primary challenge to producing viable seedlings. The beetles, which are known to infest all kinds of seeds and beans, spoiled most of the seeds left exposed on the forest floor. Unlike the regurgitated seeds of the sambar deer, the seeds went through the elephants’ digestive system and were covered by excrement. The seeds were protected from beetles and provided with an effective, natural fertilizer and were able to survive and grow into seedlings.

It is easy to think of animals adapting to their environment through evolution and behavioral change, but we rarely consider the same relationship in the opposite direction. The massive Platymitra macrocarpa has perhaps evolved to provide fruit that appeals to more than one frugivore.

Also Read-Breaking the Law? Sri Lanka Cracks Down on Owners of Elephants taken from Wild

As McConkey told VOA, “The husk of the fruit — it’s like the outer covering of the fruit — has become very thick, and it’s that outer covering that deer eat. But if you open up the fruit, each seed is covered by this juicy, soft pulp, and it’s that that the monkeys and gibbons like.” She thinks that this might be a case where the tree evolved to appeal to multiple animal species to increase the chance of spreading viable seeds.

Despite the variety of animals eating the seeds, elephants are still the tree’s best chance of producing viable seedlings. When asked what might happen if elephants were to disappear from the region, Brodie responded, “That’s the million-dollar question.” (VOA)