Humpback whales caught singing in New York’s waterways during winter seasons raise intriguing questions about the mammals’ captivating behaviors and how the Northern Hemisphere is adapting to climate change.

The whales in this region spend most of their year in the North Atlantic but then head south for the winter. These aquatic snowbirds roost in the Caribbean, where they sing and breed in the tropical waters.

New York waters were previously considered a thoroughfare for this annual migration--but lately humpback sightings are occurring in the mid-Atlantic during the winter, too. The state’s Department of Environmental Conservation (DEC) had previously recorded humpback singing during the winter of 2017-2018 in the New York Bight, an area of the Atlantic Ocean from New York Harbor east to Fire Island and south to the Manasquan Inlet. The state monitors whale activity there, in a roughly 16,740-square-mile zone south from Long Island to the Outer Continental Shelf.

“The traditional paradigm for humpback whale song is that it's produced by males on the breeding grounds, which are for these whales around the Caribbean — so it's not something that you necessarily expect to find further north,” said Julia Zeh, an environmental biologist and doctoral student at Syracuse University. “There have been records of song around Massachusetts and also even further north. And so that brought up a lot of questions about what are the whales doing in waters around New York? When are they here, and why are they here?”

Zeh co-led a study published last December in Marine Mammal Science, where marine researchers analyzed audio data from 2008-2009 captured from underwater recorders in the New York Bight. The project, a collaboration between the Wildlife Conservation Society, Cornell University, Columbia University and Syracuse University, reviewed about 6,300 hours of recordings.

Here's a sample of what these recordings captured:

The team used an algorithm to isolate the humpback whale songs recorded in an area 70 miles south of Long Island. They found the whales were singing in the winter and spring months of 2008, Zeh said, adding that it is the earliest known evidence of this behavior in the New York Bight.

“The fact that we recorded it in winter, when they're traditionally thought to have already migrated to their equatorial breeding grounds, was really the most surprising thing,” Zeh said. This unconventional soundtrack could signal that younger, immature male whales don’t always make the journey south for reasons yet unknown.

“Whales may remain in waters further north longer because they’re not old enough to mate,” Stephanie Rekemeyer, a DEC spokesperson in the division of Marine Resources, said in an email. “There have been some whales observed over-wintering in the northeast region, and scientists are monitoring these occurrences.”

The data could also mean that humpback whales are turning the New York Bight into a mating ground, and Rekemeyer said studies are underway to look into this possibility. But the whale recordings arrive as sightings in the New York area, including in the winter months, are rising.

“It's showing that there are whales here during a time when we didn't think there were so many in the area,” said Rutgers scientist Danielle Brown, who is the lead researcher for the Gotham Whale marine advocacy group and who was not affiliated with Zeh’s study.

Humpback whale sightings in the New York and New Jersey regions have increased in the past decade, from 5 sightings in 2011 up to 272 sightings in 2018, with many sightings less than two miles from shore. Researchers say the 2008 song recordings from Zeh’s team predate this uptick and do not correlate with the region’s increased whale activity, so it’s hard to say what they mean.

Humpback whales in the New York Bight

More recent observations show the whales are coming to feed here as numbers of their favored prey, menhaden, have increased, said Paul Sieswerda, executive director Gotham Whale, an advocacy group for whales.

Some climate change studies point to shifts in whale migration movements as oceans warm. Others suggest that the heat may be affecting food access and pregnancy rates for whales summer farther north in Canadian waters. But the DEC says the increased sightings of whales off New York’s shores could be attributed to warm water temperatures lasting longer into the winter and food sources remaining abundant in the area.

More research is needed to understand why more humpback whales are hanging around New York, Sieswerda added, whether it’s related to warming waters and climate change or other environmental factors.

These investigations can help determine how to protect the whales better if they’re lingering in what is one of the busiest, “most urbanized waterways on the planet,” said

Dr. Howard Rosenbaum of WCS’s Ocean Giants Program, who co-authored Zeh’s study, added that the increased whale presence in the mid-Atlantic has also meant “half of the (whale) mortalities along the Eastern seaboard are attributed to some human-related role, whether that's getting hit by a ship or entangled in a fishing net.”

“We have to begin to think about ways in which we can use this information to mitigate threats to them and better protect them in these environments,” Rosenbaum said.

Emily Lang and Danny Lewis contributed to reporting.