A tiny songbird is capable of travelling more than 1,500 miles non-stop over the Atlantic Ocean in three days while taking its annual migration route, according to a study published Tuesday in the journal Biology Letters.

For decades, scientists have been baffled by whether the blackpoll warbler, a small songbird with a black cap, white cheeks and white wing bars, flew over the Atlantic -- a journey of nearly 2,500 kilometers (about 1,553 miles) -- without landing on the eastern coast of the United States. In a bid to confirm the bird’s annual migration route and distance it covers, the researchers outfitted the bird with even tinier tracking devices, dubbed “backpacks.”

“This is the first study to provide direct evidence of the birds’ migration route – we found they flew directly over the Atlantic Ocean to reach their wintering grounds in South America,” Ryan Norris, a professor at the University of Guelph in Ontario, Canada, and the study’s co-author, said in a statement.

Found in boreal forests of Canada and the U.S. from spring until early fall, blackpoll warblers weighs only about 12 grams. They spend summers in the forests extending across North America, before migrating to South America for the winter.

As part of the study, the researchers used tiny geo-locators -- each weighing only 0.5 gram -- to track blackpolls on their annual flight south to the Caribbean, and on their way north to Canada and the U.S. in the spring. The devices, which were fitted on the backs of the birds, were so small that they were not able to transmit the data remotely and researchers had to wait until the birds returned.

“We waited for them to return in the spring and then searched the forest to find the blackpolls with geo-locators,” William DeLuca of the University of Massachusetts and the study’s co-author, said in the statement. “When we accessed the locators, we saw the blackpolls’ journey was indeed directly over the Atlantic. The distances travelled ranged from 2,270 to 2,770 km.”

According to researchers, blackpoll warblers build up their fat stores to prepare for the flight. They eat as much as possible so they can fly without needing food or water.

"They are just sheathed in a layer of fat that makes them look like little butter balls," Chris Rimmer of the Vermont Center for Ecostudies in Norwich and a co-author of the study, told Live Science.