Why do whales migrate?

Quick Answer

Whales migrate to balance two essential survival needs: feeding and reproduction. Cold polar waters offer massive concentrations of prey like krill and small fish, making them ideal summer feeding grounds. However, these frigid environments are dangerous for newborn calves, so whales travel thousands of miles to warmer tropical or subtropical waters to breed and give birth each winter. The gray whale holds the record for the longest migration of any mammal — up to 12,000 miles round trip annually. This extraordinary seasonal journey is one of the most remarkable examples of whale behavior in the animal kingdom.

What You Need to Know

Feeding Drives the Summer Journey North

The primary engine behind whale migration is food. During spring and summer, polar and subpolar oceans experience massive plankton blooms fueled by long daylight hours and upwelling nutrients. These blooms support enormous swarms of krill, copepods, and schooling fish — the dietary staples of most baleen whales.

Species like the blue whale can consume up to 4 tons of krill per day during peak feeding season, packing on thick layers of blubber that serve as energy reserves for the months ahead. Humpback whales employ cooperative bubble-net feeding strategies in these rich northern waters, working together to corral prey into tight clusters. To learn more about whale diets, see what do whales eat.

These cold-water feeding grounds stretch across regions like the Gulf of Alaska, the Bering Sea, the Antarctic Ocean, and the nutrient-rich waters off Iceland and Norway. Whales spend roughly four to six months gorging in these productive habitats before the seasonal shift begins.

Breeding and Calving Pull Them South

As autumn arrives and polar food supplies dwindle, whales begin their long journey toward warmer waters near the equator. The primary reason is reproduction. Warm, calm, shallow waters provide three critical advantages for breeding and calving:

• Thermal protection for calves. Newborn whales are born with very little blubber. In freezing polar seas, a calf would lose body heat far too quickly to survive. Warm tropical waters — typically between 70°F and 82°F (21°C–28°C) — give calves vital weeks to nurse, grow, and build insulating fat.
• Calmer sea conditions. Sheltered bays, lagoons, and reef-protected coastlines offer gentler waters where mothers and calves can bond without battling heavy swells and storms common in higher latitudes.
• Reduced predation risk. While predators like killer whales range widely, the shallow, warm-water calving grounds offer fewer hunting opportunities for large predators compared to the open deep ocean.

Female whales nurse their calves on extraordinarily fat-rich milk — sometimes containing 35–50% fat — which helps calves grow rapidly. A humpback whale calf, for instance, can gain roughly 100 pounds per day during the nursing period.

The Physical Cost of Migration

Migration is not without sacrifice. Most baleen whales eat little to nothing during the winter breeding season. They survive almost entirely on the fat reserves accumulated during their summer feeding binge. Humpback whales may lose up to a third of their body weight over the course of a single migration cycle.

This fasting period is especially demanding for nursing mothers, who are simultaneously sustaining their own bodies and producing hundreds of liters of milk for their growing calves. It is an extraordinary physiological feat that underscores why productive summer feeding grounds are so critical to whale survival.

Not All Whales Follow the Same Pattern

It is important to note that migration is not universal across all whale species. Baleen whales — including humpbacks, grays, right whales, blue whales, and fin whales — are the most well-known long-distance migrants. But several species break the mold:

• Bowhead whales remain in Arctic and sub-Arctic waters year-round, shifting only short distances with the advance and retreat of sea ice.
• Some populations of killer whales are resident, staying in one region throughout the year and following local prey like salmon rather than undertaking long-distance seasonal movements.
• Sperm whales have a more complex pattern: males may travel to higher latitudes to feed, while females and young tend to stay in warmer tropical waters year-round.

Even among migratory species, not every individual migrates every year. Some juveniles or non-breeding adults may skip the journey if conditions allow, remaining in or near feeding areas through winter.

Climate Change and Migration Disruption

Warming oceans are beginning to alter whale migration patterns. As water temperatures rise, prey species like krill are shifting their distribution, forcing whales to adjust their routes and timing. Researchers have documented humpback whales arriving later at traditional breeding grounds and some populations shortening their migrations altogether.

Changes in sea ice also affect species like the gray whale, whose Arctic feeding habitat is intimately tied to seasonal ice cycles. These disruptions add stress to already demanding migration journeys and are a growing focus of conservation efforts worldwide.

Ship strikes and entanglement in fishing gear pose additional threats along busy migration corridors, particularly for endangered right whales migrating along the eastern seaboard of North America.

Key Takeaways

• Whales migrate primarily to feed in cold, productive polar waters during summer and breed in warm, protected tropical waters during winter.
• The gray whale completes the longest mammalian migration on Earth — up to 12,000 miles round trip each year.
• Newborn calves need warm water because they lack sufficient blubber to survive polar temperatures.
• Migrating whales fast for months, surviving on stored fat reserves, with nursing mothers bearing the greatest physical cost.
• Not all species migrate long distances — bowhead whales and some killer whale populations remain in the same waters year-round.
• Climate change is disrupting traditional migration routes and timing by shifting prey distribution and altering ocean temperatures, making conservation efforts increasingly urgent.
• To learn about other fascinating whale behaviors, explore why do whales breach and how do whales sleep.