Whale

C

Digestive System

When whales swallow food, it travels through the esophagus to a multichambered stomach that resembles the stomachs of ruminant hoofed animals such as cattle, sheep, and deer. In the first stomach chamber, a saclike extension of the esophagus, food is crushed. In the second chamber, digestive juices further break down food. Most cetaceans have a third stomach chamber, which regularly contracts to mash and thoroughly mix food with digestive juices. The stomach capacity of a large whale can reach 760 liters (200 gallons).

From the stomach food moves through the intestine, where nutrients pass through the intestinal wall and are absorbed into the blood. Remaining waste materials are eliminated through the anus into the ocean. Cetaceans lack two internal organs found in most land mammals: the gallbladder and appendix.

D

Sense Organs

The eyes of most whales are well adapted for life underwater. Strong muscles surrounding each eye change the shape of the eye’s lens. This enables whales to focus their vision both underwater and above water. Whale eyes can withstand high pressure when the animal dives to great depths, and the tear ducts shed oily tears that enhance underwater vision and protect the eyes from the effects of salt water.

The streamlined bodies of whales do not have the external ear structures called pinnae that land mammals use to gather airborne sound. But whales still have excellent hearing and can perceive a wide range of sounds, many of which are not audible to humans. For toothed whales that commonly hunt for food in the dark depths of the ocean, hearing is often enhanced by echolocation, in which the animals emit clicking sounds that bounce off objects. The returning echo is used as a sonar image of the underwater surroundings. Toothed whales share this ability with bats, shrews, and a few kinds of birds.

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Baleen whales have a poor sense of smell, and toothed whales lack smell entirely. Some whales, such as dolphins, can taste different chemicals in water to differentiate between sweet, sour, bitter, and salty, but in general the sense of taste in whales is limited.

III

Behavior of Whales

Studies of whales in captivity have taught scientists much about the complex social behavior of whales. Since the late 1980s, advances in the use of satellite tracking systems have also broadened opportunities for scientists to observe how whales behave in the wild.

A

Swimming and Diving

Whales swim by making powerful up-and-down movements of the tail flukes, which provide thrust. The power comes from body muscles that flex the lower spine up and down in a wavelike motion. The whale’s flippers help the animal steer. In some species, such as humpbacks, the flippers are large and powerful and may be used for fighting among males or, more rarely, for warding off attacks by killer whales.

Most whales remain near the surface of the ocean, but some dive to great depths and remain underwater for long periods ranging from 50 to 80 minutes. Whales possess interesting adaptations for diving, some of which are shared with other aquatic mammals such as seals. For example, whale lungs and adjoining air passages collapse under the pressure of a dive, forcing air into central parts of the lungs and thereby reducing the amount of nitrogen absorbed into the bloodstream. Too much nitrogen in the bloodstream can cause decompression sickness and a disorienting condition known as nitrogen narcosis. At the same time the whale’s blood and muscles contain high concentrations of the oxygen-storing pigments hemoglobin and myoglobin. During prolonged dives these pigments supply 80 to 90 percent of the whale's oxygen.

Also during a dive, the whale’s heart rate slows to as low as three to five beats per minute. Arteries constrict, greatly reducing blood flow to many of the animal's organs. This conserves oxygen and maintains blood pressure in the life-supporting structures, such as the brain and heart.

During a dive, the lack of oxygen in the whale’s body triggers the buildup of lactic acid, a chemical produced when body tissues obtain energy by metabolizing sugar in the absence of oxygen. In most animals the buildup of lactic acid in muscle leads to fatigue and can cause cramps. For reasons not well understood, whales can tolerate the pain and fatigue caused by lactic acid accumulation in muscle tissue, enabling them to remain underwater for long periods. Baleen whales can hold their breath up to 50 minutes when diving, and of the toothed whales, sperm whales can hold their breath up to 80 minutes.

Some whales, such as killer whales, regularly jump clear of the water and land on their back or side in a behavior known as breaching. Scientists are unsure why whales breach. Some theorize that this behavior may be a display of dominance used in courtship or may enable the whales to view their surrounding area. The loud sound that breaching makes as the whale lands in the water suggests to some scientists that it is used as a form of long-distance communication.

B

Migration

Migration is a regular occurrence in many whale species. Most baleen whales migrate great distances to spend their summer months in the cooler waters of polar regions. There they feed on small shrimplike organisms called krill, as well as on other invertebrates and fish. During the fall these whales migrate to warmer waters to breed. Gray whales may travel up to 10,000 km (6,200 mi) from their feeding grounds off the coast of Alaska to their breeding grounds along Mexico’s shores. Some humpback whales feed in the Southern Ocean around the Antarctic Peninsula and travel north of the equator to breed in the waters along Colombia. Toothed whales tend to travel in a nomadic fashion and do not exhibit regular long-distance migrations. One exception is the male sperm whale, which migrates long distances between mating and calving grounds near the equator and feeding areas in polar waters.

Depending on the species, sex, age, and season, whales may travel alone, in pairs, or in small or large groups. A group of about 20 or fewer whales is called a pod; larger gatherings are called schools. Some groups consist only of males and some of both males and females. In some species, such as the pilot whale, the groups appear to have definite leaders. Killer whales live in family groups called matrilines. Each matriline is composed of an adult female and her offspring. Male parents of offspring do not live with the matrilineal group. Some male and female offspring stay with their matrilineal group for life, while other matrilineal groups are less stable, with members that come and go. Two or more matrilines may travel together in a pod.

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