Ontario researchers have led an international team that tracked an "incredible" 20,000-kilometre voyage by a tiny songbird in an effort to understand why its population has collapsed and how it can be saved.

Ryan Norris, an ecology professor at the University of Guelph, and his team discovered that the blackpoll warbler, which weighs the same as two loonies, migrates from its breeding grounds in northwest North America to the eastern seaboard where it refuels.

Then it takes a straight, non-stop shot south over the Atlantic Ocean to its winter grounds in the Amazon basin. Then they go back again. The blackpolls repeat that journey every year.

"That whole round trip is incredible for a bird that size," Norris said, "just incredible."

Incredible is a word Norris uses often about the bird. In 2015, using "incredible little backpacks" strapped to the birds for tracking, Norris and his team showed for the first time that blackpolls fly from the Maritimes and Vermont south over the Atlantic Ocean to the greater Antilles where they stop for a time before pushing on to Venezuela and Colombia.

Until then, most people knew the birds, which have undergone a rapid population decline over the last several decades, vanished from the eastern seaboard and then reappeared in South America each year. No one really knew how they got there, he said.

That changed when tracking technology got down to a certain weight -- half a gram -- to be used on the small songbirds.

Now Norris and his colleagues are filling in the gaps on the blackpoll, especially from its western breeding grounds.

"We need to know where these birds are going if we're going to do anything effective for them," Norris said. "We can't just know where they breed -- they are only up there for two months of the year. If we don't know where they go for the rest of the year, we can't make any progress on conservation."

The tracking technology, known as light-level geolocators, will be a boon to conservation efforts, he said.

"It's an incredible and incredibly simple device," Norris said. "It has a clock and a light sensor and a small battery. People navigated hundreds of years ago around the world with a clock and light."

How long the sun has been up is the latitude estimate while when the sun comes up relative to a standard time is the estimate for longitude, Norris explained.

The problem for researchers is that the devices do not use GPS technology because those remain too heavy due to the battery needed to power it. The tracking device does not transmit the data it collects -- that would require a much larger battery -- so researchers have to catch the birds, place a harness on them and affix the devices to their backs. They also identify them with leg bands.

Then they need to catch that bird in order to access the data, Norris explained.

"It's very hard work," he said.

The team returned to specific locations in forests in Nome and Denali, Alaska, Whitehorse, Yukon, and Churchill, Man.

"We tagged 111 birds and got 27 back," Norris said.

Buried in the data are incredible stories, he said.

The birds' flight home to Canada and Alaska was, on average, 34 days. It was nearly double that time going south.

The birds also leave South America at different times depending on the lengths they need to fly to return home.

"One bird knows that is has to leave earlier than the other bird, which is incredible," Norris said.

"They have similar habitats and could even be neighbours on the wintering grounds, but one's like 'I gotta get going, I got a longer journey.' And they arrive back on the breeding sites around the same time, which is incredible."