Recent findings of bone fragments from Alaska indicate that birds have been nesting and breeding in the Arctic for at least 73 million years.

“It’s quite unusual, as raising a newborn in the Arctic is challenging,” explains study author Lauren Wilson from Princeton University.

Currently, around 250 bird species can thrive at the poles. Some migrate great distances to enjoy continuous daylight in summer, while others brave the winter, enduring extreme cold and long periods of darkness. However, knowledge about how these birds first adapted to the highest latitudes remains limited.

Wilson and her team searched for ancient avian traces within the Princreek Formation in northern Alaska, which formed on coastal floodplains about 73 million years ago. At that time, northern Alaska was approximately 1,000-1,600 kilometers closer to the Arctic than it is today.

The researchers retrieved ancient soil samples from several narrow rock layers, encountering temperatures of -30°C (-22°F) in a makeshift tent. “This has definitely been the most demanding fieldwork I’ve undertaken,” Wilson admits.

Back at the lab, they spent hours peering through microscopes at sediments smaller than two millimeters, hunting for tiny fossil bone fragments.

The team uncovered over 50 fossil fragments belonging to ancient birds, primarily from chicks and even embryos. The fossilized bones of these young birds exhibit a sponge-like texture, indicative of rapid bone growth.

Although birds likely began nesting in the Arctic Circle 73 million years ago, these fossils represent the earliest evidence of such behavior, extending the timeline of avian presence back by 30 million years.

However, many fossils are fragmented and do not clarify whether these birds remained year-round or only in the warm summer months.

“The Arctic’s food web, which supports life in extreme cold and darkness, couldn’t exist without the plethora of birds that inhabit high latitudes,” says Steve Brusatte from the University of Edinburgh, who wasn’t involved in the study. “These fossils illustrate that birds have been a vital part of these high-latitude ecosystems for tens of millions of years.”

Wilson’s team identified three major bird groups represented among the fossil fragments: extinct tooth-like birds similar to ducks, extinct tooth-like birds reminiscent of gulls, and various species that may be related to modern birds.

Conversely, the samples did not include bones from older bird groups known as enantiornithines, or “opposite birds.” Gerald Mayle from the Senckenberg Institute in Germany, who also wasn’t part of the study, noted that this finding suggests that more advanced bird ancestors could survive the harsh Arctic conditions due to certain evolutionary advantages that older birds lacked.

The ecosystems that shaped the Princreek Formation existed when non-avian dinosaurs dominated the planet, with evidence that ancient birds coexisted with species like tyrannosaurs and horned ceratopsians in these Arctic environments. Some dinosaurs even nested within the Arctic Circle.