Off the coast of Western Australia, a humpback whale is “pirouetting”, sweeping its pectoral fins through the water, its massive jaw hanging wide open. Surrounded by companions, the animal isn’t lunging for a meal: rather, it is putting on a mysterious behavioural display.

This underwater ballet, captured on camera by an onlooker and shared online, is one of the clearest examples of a rarely documented phenomenon known as “gaping”.

As autumn chills Australia’s east and west coasts, the ocean transforms into a bustling humpback highway. May marks the mammals’ annual migration from Antarctic waters to the warmer breeding grounds of Queensland, northern New South Wales and the Ningaloo coast to the Kimberley region in WA – and for those with shoreline views, it heralds the start of whale-watching season.

Just in time for this year’s migration, a Macquarie University study has proven the power of citizen science. Social media footage of 66 humpbacks – including WA’s pirouetting whale – reveals their mysterious jaw-gaping behaviour could be a social display.

“Just when we think we know a lot about humpback whales, we don’t,” says Dr Vanessa Pirotta, a renowned Australian whale scientist and co-author of the paper. “Tourism operators and citizen scientists spend hours observing whales and are a powerful resource for capturing and reporting on behaviour.”

The researchers have termed the behaviour “gaping”, and believe it could be play, social signalling, interacting with debris or calves stretching their jaws around mealtimes.

“It was so unusual to see this happen,” Pirotta says. “And when I heard the commentary of people watching it, I knew it was rare.”

Veteran humpback researcher Dr Olaf Meynecke, currently surveying marine life off South Australia on the CSIRO research vessel Investigator, says baleen whales typically open their jaws wide when feeding.

“Concentrated prey, either fish or krill on the surface, is being taken in by [the whale] coming from the depth and lunging out with a wide open mouth,” Meynecke says.

“Humpback whales can achieve this by working together to create rings of bubbles, forcing prey to concentrate on the surface and then coordinating amongst each other [to determine] who is allowed to get the lunge from the middle … [it’s] fantastic to observe, as a lot of speed and force is involved.”

The Organisation for the Rescue and Research of Cetaceans in Australia (Orrca) says the behaviour is often associated with “lunge feeding … a highly efficient feeding strategy”, where a whale accelerates, engulfs a massive volume of water, and expels it through their baleen plates to trap prey.

While the exact purpose behind gaping remains debated, the new paper suggests it is a distinct behaviour.

Documented in breeding grounds and migratory routes where whales are often actively fasting, gaping lacks the acceleration, prey capture and dramatic throat expansion of a feeding lunge. The mouth hangs open, sometimes above water, sometimes below.

Katie Trepess, managing director of Whale Tales Whale Watching in Sydney, says that observing this on the east coast is particularly special.

“Humpback whales are generally not feeding during the four to six months of the migration into warmer waters when they are travelling and breeding; instead they are relying on fat reserves,” Trepess says.

She has observed a rise in “mugging”, when whales lift their heads out of the water to look at people on board boats, referred to as a “spyhop”.

She says there have already been whale sightings along the east coast, despite whale migration typically running from mid-May until mid-November. Her team plans to start going out for daily whale encounters from 22 May.

One of nature’s great migrations

The 2026 season has already been demanding for whale rescue crews.

After 19 strandings and 28 entanglements across NSW in 2025, rescue organisation Orrca saw its March hotline calls spike 93%.

As whales migrate closer to the shore, increased coastal activity heightens the risk of vessel strikes and fishing gear entanglements.

“This is one of nature’s great migrations, but it’s also one of its most vulnerable,” Orrca’s president, Ashley Ryan, says. “We’re already seeing increased whale activity along our coastline and that means increased risk.”

Meynecke says a lack of funding means citizen scientists are now the “main drivers” tracking whales in Australia. With whales forced to rapidly adapt to climate change, melting sea ice, pollution and overfishing, continuous monitoring is crucial to their survival.

Ahead of Orrca’s annual whale census on 28 June, authorities are reminding the public to keep their distance. All vessels, surfboards and drones must stay 100 metres from whales, extending to 300 metres for jetskis or when calves are present.

“Simple actions make a huge difference,” Ryan says. “Keeping your distance helps ensure these animals can continue their journey safely.”

Where to watch the migration in NSW

For those hoping to catch a glimpse of the migration, NSW National Parks and Wildlife Service (NPWS) has highlighted dozens of land-based vantage points along the coast.

In Sydney and its surrounds, prime spotting locations include Cape Solander in Kamay Botany Bay national park, Barrenjoey Lighthouse in Ku-ring-gai Chase national park and the North Head and South Head trails in Sydney Harbour national park. Locals also say walking tracks along beaches at Sydney’s Royal national park offer excellent vantage points.

Onlookers can also head to Cape Byron Lighthouse in the state’s north, the Yuraygir coastal walk near Coffs Harbour, the Cape Hawke lookout in Booti Booti national park and the Tomaree Head Summit walk in Port Stephens. Down south, the spectacular views from Seven Mile Beach in Jervis Bay, Montague Island near Batemans Bay and the Green Cape lookout in Eden offer phenomenal viewing opportunities.

To capture a whale’s rare “gape”, a local boat tour might offer the closest view.

“It’s lovely to spot whales from the coastline, but being out on the water with them is really the only way to properly experience whales and get a feel for their beauty and size,” Trepass says.

“Humpback whales are naturally quite playful and inquisitive … we see young whales jumping and splashing around and learning how to breach and head lunge.”