The Great Barrier Reef is home to some of the most incredible animals on Earth. The Great Barrier Reef is blessed with these fantastic creatures and their memorable displays of behaviour.
Every June, around 60,000 humpback whales leave Antarctica and start swimming north. By the time they pass Cairns, they’ve already covered roughly 4,000 km on almost nothing to eat. What you see from a reef vessel, the breaching, the spy hopping, the tail slaps, isn’t random spectacle. Each behaviour has a function. Knowing what you’re looking at changes the experience.
Humpbacks pass through Cairns waters from June through October, with peak numbers in July, August, and September. Here’s why they’re here and what their surface behaviours actually mean.
Why Humpback Whales Are in Queensland Waters
Antarctica is one of the most productive feeding environments on earth. Krill blooms during the southern summer and humpbacks spend months there building up energy reserves. But the feeding season ends. As Antarctic winter sets in, krill stocks fall and sea ice forms. The whales head north.
The journey is approximately 6,500 to 8,000 km one way. Humpbacks don’t travel in a straight line, and they don’t all travel together. Juveniles tend to lead. Expectant mothers travel more slowly and stay in calmer water where possible.
What makes this migration unusual is that humpbacks eat almost nothing during it. They run on blubber built up during the Antarctic summer. The entire round trip runs on stored fat. By the time a whale reaches Queensland, it’s been living off reserves for weeks.
Queensland is the breeding and calving ground. Calves are born relatively helpless and need warm, sheltered water to feed, grow, and learn the behaviours that will keep them alive. Humpbacks return to the same grounds where they were born, navigating by magnetic fields, ocean currents, and temperature gradients.
When to See Humpback Whales from Cairns
Season runs from June to October. Peak sightings happen in July, August, and September, when whale numbers are highest and activity is most concentrated.
Around 60,000 humpbacks migrate up Australia’s east coast each year. The east Australian population was hunted to near-collapse in the 20th century and has been recovering since the 1963 whaling ban. The numbers today are encouraging. Cairns sits directly in the migration corridor, and sightings from reef vessels during peak season are common.
A Guide to Humpback Whale Behaviour
The table below is a quick reference. The sections that follow explain each behaviour in more detail.
| Behaviour | What it looks like | What researchers believe it means |
|---|---|---|
| Breaching | Full or partial leap from the water | Courtship, communication, parasite removal |
| Spy hopping | Slow vertical rise until the eye clears the surface | Visual reconnaissance |
| Pec slapping | Rolling and slapping a pectoral fin on the surface | Play and social communication |
| Lobtailing | Raising the tail fluke and slapping the surface | Communication, possible agitation |
| Peduncle throw | Lateral throw of the tail section | Dominance display between competing males |
| Milling | Slow, calm surface movement with no dramatic displays | Resting or socialising |
Breaching
A breach is a full or near-full body leap from the water, followed by a crash back onto the surface. It’s the most physically demanding behaviour a humpback performs.
Researchers believe breaching serves multiple purposes simultaneously: courtship display, long-distance communication (the sound of a 40-tonne animal hitting water travels far), removing barnacles and parasites from the skin, and teaching calves. You’ll sometimes see a whale breach ten or twenty times in a row. That repetition is deliberate. A single breach burns real energy. If a whale keeps going, something is happening that warrants it.
Spy Hopping
Spy hopping is quieter than breaching and often missed. The whale rises slowly and vertically until one eye clears the surface, holds the position briefly, then sinks back. No splash. No drama.
The most accepted interpretation is simple: the whale is having a look. Humpbacks are curious animals and spy hopping near boats is common. They’re watching you as much as you’re watching them.
Pectoral Fin Slapping
A humpback’s pectoral fins are remarkably long, up to a third of its body length. Pec slapping involves the whale rolling onto one side and bringing a fin down hard on the surface. The sound carries some distance.
This behaviour is associated with play and social communication. It’s common in juveniles and in groups where animals are actively interacting. Calves do it frequently, often mimicking adults nearby.
Lobtailing
Lobtailing means lifting the tail fluke clear of the water and slapping the surface with force. The splash is significant and the sound distinct.
Researchers associate lobtailing with communication. It can also signal agitation or alertness. If a vessel approaches too close, lobtailing may follow. Experienced guides can read the difference between a relaxed display and a stressed animal.
Peduncle Throw
The peduncle is the muscular section connecting the whale’s body to its tail flukes. A peduncle throw pushes this section laterally out of the water in a forceful, aggressive movement.
This behaviour is most often seen between competing males during the breeding season. It’s a dominance display: physically imposing, unmistakable, and usually directed at a rival.
Milling
Not every surface behaviour is dramatic. Milling is slow, calm movement at the surface with no obvious displays. The whale is resting or socialising.
It’s easy to underestimate as a quiet sighting, but watching a 15-metre animal move through the water with no apparent urgency is worth your attention. These are the moments that tend to stay with people.
A Note on Research
Most of these interpretations come from decades of observational fieldwork. Many humpback behaviours are still being studied and almost certainly serve more than one purpose at once. A breaching whale might be communicating, removing parasites, and displaying fitness simultaneously. Single explanations rarely cover all the contexts in which any given behaviour appears.
Humpback Whale Song
Male humpbacks sing during the breeding season. The songs are long, complex, and layered. What’s unusual about them is that all males in a population sing the same song at any given point in the season, and that song changes gradually as the season progresses. By the time the whales head south again, the song is different from how it started.
Songs can travel hundreds of kilometres through water. If you’re diving or snorkelling near a singing whale and conditions are right, you can feel the vibration through the water. It’s one of the more disorienting and memorable things that can happen on a reef trip.
Only males sing. The precise function remains debated, but the dominant theory is mate attraction.
Mothers and Calves
Calves are born in tropical waters and are completely dependent at birth. A newborn can weigh close to 900 kg and measure around four to five metres, but it has everything to learn.
Calves mimic their mothers. You’ll see them attempting breaches alongside a larger adult, copying fin slaps, learning the timing and rhythm of surface behaviours through repetition. Mother-calf pairs are often identifiable at a distance by the smaller second splash alongside a larger one.
These pairs travel more slowly and stay in calmer, shallower water where possible. Mothers are protective. Guides keep a careful distance from mother-calf pairs, and responsible tour operators will not pressure a boat toward them.
A humpback breach is one thing as a spectacle. It’s another thing when you know the animal has already swum 4,000 km without eating, is running on stored fat, and is likely displaying for a mate or signalling to another whale hundreds of metres away.
Whale watching tours from Cairns run June through October. View Great Barrier Reef Tour options here.
Frequently Asked Questions
When is humpback whale season in Cairns?
June to October, with peak activity in July, August, and September. This aligns with the annual migration of humpbacks up Australia’s east coast to their Queensland breeding and calving grounds.
How do I see humpback whales from Cairns?
Reef vessels passing through the migration corridor encounter whales regularly during peak season. Dedicated whale watching tours also operate from Cairns during this period.
Why do humpback whales breach?
Breaching likely serves multiple purposes: courtship display, long-distance communication, and removing barnacles and parasites. The specific function varies with context. Repeated breaching in a group usually signals social interaction or competition between males.
What does it mean when a whale spy hops?
The whale is looking. It rises vertically until one eye clears the surface, holds the position, scans its surroundings, then sinks back. Humpbacks are curious. Spy hopping near boats is common.
How far do humpback whales migrate in Australia?
Around 6,500 to 8,000 km one way, from Antarctic feeding grounds to Queensland breeding waters and back. The east Australian migration route runs the full length of the coast.
Can you see humpback whales from shore in Cairns?
Sightings from shore are possible but uncommon. Most reliable encounters happen from reef vessels operating in the outer reef corridor during peak migration season.
What is the difference between a breach and a tail slap?
A breach is a full or near-full body leap from the water. A tail slap (lobtailing) involves lifting only the tail fluke and striking the surface. Breaching is more physically demanding and dramatic. Lobtailing is more often linked to communication or agitation.