How Baleen Whales Work

Early baleen whales started appearing about 30 million years ago [source: Carwardine et al.]. Now, there are 11 types of baleen whales divided into four different families:

These whales are generally built like other members of the order Cetacea. They have flippers, which help them to steer, and blowholes, which allow them to breathe. The tail is made of two lobes called flukes. The tail moves up and down (as opposed to the side-to-side movement of most fish) to propel the whale through the water. Their torpedo shape also helps them to move through the water and makes them very quick swimmers when necessary.

One body part that baleen whales lack is a vocal cord, but they're still able to make sounds. While toothed whales practice echolocation, or emitting high frequency sounds to find objects, baleen whales make sounds at much lower frequencies that resemble moans and belches. Because baleen whales have a good sense of hearing, it's possible they're communicating with whales hundreds of kilometers away [source: Evans]. One particularly noisy whale is the humpback, the romantic of the sea. This whale sings complex songs, perhaps to attract potential mates.

A few features make up the differences among the baleen whales. The right whales don't have a dorsal fin, and they also don't have throat grooves, which are a big key to a rorqual whale's identity. We'll talk more about the role of throat grooves a bit later. Rorquals have a small dorsal fin, while the gray whale has more of a small dorsal hump.

Other differences are more cosmetic: Humpback whales have the longest flippers of any whale, with the appendages growing to about one-third of the length of the whale [source: Carwardine et al.]. Right whales are often identified by the callosities on their head, which are rough patches of skin. Bryde's whales have three ridges on their head, while other whales have just one.

Baleen whales are some of the largest animals in the world, with one exception being the pygmy right whale, which typically grows no longer than 20 feet (6 meters). The blue whale, which has been measured at almost 100 feet (30 meters) in length and weighs 200 tons, is the biggest. Coming in second is the fin whale, which can measure up to 89 feet (27 meters). In general, baleen whales weigh about 1 ton for each foot of length. Females are larger than males; for example, humpback whales measure approximately 45 feet to 50 feet (14 meters to 15 meters), with males measuring about 3 feet (1 meter) shorter.

What all baleen whales have in common is filter feeding, but the rorqual, right and gray whales all go about this practice in a different way. We'll take a closer look at their different feeding methods on the next page.

Baleen whales practice filter feeding, and the tools for filter feeding are their baleen plates. Baleen plates are made of keratin, which is the same material found in our fingernails and our hair. The baleen plates are worn down by the whale's tongue, but they also grow back like fingernails. Whales have hundreds of baleen plates. For example, the humpback whale has 400 baleen plates, each of which is 25 inches to 30 inches long (64 cm to 76 cm), 13 inches (33 cm) wide and less than 0.2 inches (0.5 cm) thick [source: MacMillan].

On one side of the plates are coarse bristles, the fringed mustache we mentioned earlier. These bristles vary in length and thickness, but they all help the whales to trap small fish, krill and plankton. These prey items are abundant in colder waters, and the baleen's large size allows it to take advantage of the abundant prey and store the energy. The larger baleen whales eat approximately 4 percent of their body weight each day [source: SeaWorld]. Each type of baleen whale has a specific prey and a particular method of obtaining it. In other words, one filter does not feed all.

The right whales filter feed by skimming the water, which involves swimming along the surface of the water with an open mouth. As the whale swims, in comes water rich with the plankton that live on the ocean's surface.

Rorqual whales are gulpers, which means they take big swallows, find the food and filter out all the excess water. Think about the biggest swig of soda you've ever taken -- it would be no match for the rorqual whales. They take the expression "open wide" to a new level with their throat grooves. These expandable pieces of skin get so big that rorquals can take in about 18,000 gallons (68,137 liters) of water, a volume equal to a school bus.

To start this process, the rorqual whale descends several hundred feet below the surface. It swims fairly fast until it opens its mouth. At this point, the throat grooves, which are pleated like a skirt, expand so that their mouth forms a huge sac, like a parachute. While this allows huge amounts of prey to enter, it also creates tremendous drag on the whale. One sip more than doubles the whale in size for a few seconds and weighs more than it does. When the whale closes its mouth, the water is filtered through the stringy baleen before it exits back out the side of the mouth.

With each mouthful, a fin whale, a type of rorqual whale, can trap about 20 pounds (9 kilograms) of krill. That's important, because each lunge, with its fast start and abrupt stop, requires an enormous amount of energy. To offset the energy loss, these whales may hunt for about four hours a day in order to eat 1 ton of krill. The blue whale needs about 2,200 pounds (1,000 kilograms) of krill to fill its stomach.

Gray whales practice the last method of feeding, which is sucking. The gray whale swims on its side on the bottom of the ocean floor and consumes mud and dirt like a vacuum cleaner, eating for up to 20 hours a day and even leaving craters behind after a meal. From the mud and water, the gray whale filters tiny crustaceans through its baleen.

Do these huge whales have time for anything besides feeding? Find out on the next page.

Baleen whales spend hours each day filter feeding, but they also spend a lot of time migrating. Before they migrate, though, they have to store up enough food to make the trip. The krill, schooling fish and plankton that make up a baleen whale's diet are abundant in colder waters in the summer, but they disappear in the winter. Baleen whales eat a lot in the summer to prepare for the trip and compensate for a lack of prey in the winter [source: Heyning].

They migrate to warmer waters for the winter, where it takes less energy, and thus less food, to live. Baleen whales make some of the longest migratory trips of any mammal, with the humpback whale edging out the gray whale for the record. The gray whale travels 5,000 miles (8,047 kilometers) from the Bering Sea to Baja California, Mexico, in about five months [source: Ellis]. The humpback whale has been tracked from the Antarctic Peninsula to Columbia, a voyage of 5,176 miles (8,330 kilometers) [source: Carwardine et al.].

Without the pressures of feeding, baleen whales turn their attention to another matter: calving. Breeding and birthing takes place in the warmer waters, and baleen whale calves remain in the area with their mothers for a while, gaining strength and size for the colder waters.

Breeding appears to be very competitive, with several males fighting for the right to mate with a female. Sometimes, the female will mate with the most aggressive male, or she may just mate with all of them. Males have been observed taking turns and helping each other mate with the female. Females, though, usually don't mate against their will and likely mate many times to ensure success.

The gestation period for baleen whales ranges from 10 months to 14 months. If you thought pregnant women ate a lot, just wait until you hear about baleen whales. In the last half of the gestation period, females increase their food intake by 50 percent to 60 percent, which they'll store to be able to feed their calves [source: SeaWorld]. For this reason, a newly pregnant female will leave for colder waters soon after mating to start bulking up, and she'll return to the warm waters to give birth.

Observation of a whale birth is rare, but females typically give birth to one calf. At birth, the calf can swim, but not far, and is about one-quarter of the mother's length and 3 percent to 4 percent of the mother's weight [source: SeaWorld]. Males may help protect calves that could possibly be theirs, but a very close bond exists between the female and her calf. The females feed the calves frequently with milk that is about 40 percent fat for up to a year [source: Carwardine et al.]. This nursing period helps the calf get big fast, so that it can migrate and feed in colder waters as well. Blue whale calves gain about 200 pounds (90 kilograms) each day that they nurse.

While the whale calves get larger, the adult males are possibly on one of the best weight-loss programs ever. Since they don't feed during migration or breeding, they lose a lot of weight. The gray whale can lose up to about 25 percent of its body weight in the winter [source: Heyning].

Does the baleen whale calf face any predators once it makes its way into the world? Find out on the next page.

Although their large size deters many predators, baleen whales still face the threat of killer whales. Killer whales may team up to take on a large baleen whale. Large sharks also may attack baleens.

As opposed to toothed whales, which form social groups and protect each other from predators, the baleen whale is less social. The only real bond is between a mother and her calf, and the mother will fiercely protect the calf. Other baleen whales, however, don't provide any defensive help to fellow baleens in trouble.

When attacked by a bigger whale, humpback whales thrash around, trying to avoid the predator's bite, while a Bryde's whale attempts to outswim its nemesis. When it comes to fight or flight, a toothless whale usually seems to choose flight.

The baleen whale's greatest threat, however, is man. Commercial whaling has threatened baleen whales for centuries. Whale oil, made by heating a whale's blubber, was known as "liquid gold," and could be used in everything from makeup to lamps. As we mentioned, right whales were targeted for their abundant blubber and oil, and when those whales were hunted to near extinction, whalers went after other species of baleens.

While both toothed and baleen whales were victims of the whaling industry, baleen plates had some additional uses in the marketplace. Because the material is both strong and flexible, it was used to make such items as corsets, hoop skirts and whips (which is where the phrase "getting a whaling" comes from). The bristles of the plates were used to make brushes and upholster furniture.

By the time the International Whaling Commission (IWC) banned commercial whaling in 1986, no more than 5 percent to 10 percent of some whale populations remained [source: Carwardine et al.]. At least half a million fin whales and a quarter million humpbacks were killed, while northern right whales numbered only 300 at one point [source: Carwardine et al.].

But with the IWC's protective measures, baleen whale populations are generally back on track, although whales are still being killed. The IWC ruling allowed for some exceptions, including protection for native tribes who practice whaling and whales caught for scientific research, the latter being a loophole that Japan has exploited to increase whaling practices [source: Carwardine et al.].

In addition to whaling, baleen whales are still vulnerable to getting caught and tangled in fishing nets and to being struck by boats. How long baleen whales live when they're not killed by predators is unknown. Blue whales are estimated to live 30 to 90 years, and fin whales might live 90 to 100 years.

To learn more about these filter-feeding whales, take a look at the links and related HowStuffWorks articles on the next page.