One of the most intriguing aspects of whale behavior is the creatures' migration habits. Humpback whales in the Pacific Ocean will travel up and down the U.S. coast and out to Hawaii, returning to the same food-rich areas year after year. They tend to migrate with the change of seasons, taking advantage of the warmer waters nearer the equator during the colder months and the overabundance of food in the Arctic during the warmer months. Most whale species do not migrate regularly across the equator, so there may be separate collections of each species in the Northern and Southern Hemispheres.
Scientists study whale migration in a number of ways. In many species, whales have distinctive markings on their tails, which enable researchers to identify specific whales and track the sightings to get an idea of where and when the whale is traveling. Researchers also use satellite tags, cigar-sized radio transmitters that communicate with satellites to track a whale's location. Researchers embed the barbed transmitters in a whales back using a basic crossbow. Since the blubber is thick and the barb is fairly small, the whales are not hurt by the shot.
Transmitters have shown that some whale species travel much greater distances than scientists previously estimated. Researchers have tracked humpback whales traveling thousands of miles in only a few weeks, swimming from high northern latitudes to equatorial latitudes and back again. Male sperm whales seem to be solitary wanderers, traveling from ocean to ocean with no particular pattern. A single sperm whale might easily swim around the entire Earth in its 70-year lifetime.
In most other whale species, migration is closely connected to reproduction. Generally, the female whales (cows) mate in the fall or winter, when they are in warmer waters, and give birth in the same region a year or so later. In the summer, between mating and birth, the cow will take advantage of the rich food resources of the colder northern waters. This builds up the energy the cow needs to suckle its calf.
Whale calves can swim as soon as they are born, and they rise to the surface to breathe soon after birth, but they need a lot of nurturing before they can venture out on their own. Depending on the species, whales may stick to their mother's side for a year or more before joining other young whales for extended play periods. For much of this time, the calf subsists only on its mother's milk. Cows have two teats, which are normally concealed inside slits behind the whale's abdomen, near the base of the tail. Whale milk is exceptionally rich, giving the calves the nutrients they need to grow to full size in a short period of time. A baby blue whale drinks 50 gallons (189 L) of milk every day and grows by as much as 10 pounds (4.54 kg) every hour. Of course, blue-whale calves are no shrimps to begin with. A newborn calf may measure 25 feet (7.62 m) from head to tail and typically weighs more than a full-grown African elephant.
Since the gestation and rearing periods are so long in most whale species, and the suckling so draining, cows only give birth every two to four years. This slow reproductive rate means that any substantial whale hunting may have a detrimental effect on whale populations.
In the next section, we'll take a look at a fascinating acrobatic feat performed by whales -- breaching.