Continued from Introduction Page…
THE EVOLUTION OF WHALES
Sometime between 70 million and 50 million years ago, after the last of the dinosaurs had died and mammals had inherited the land, one or more groups of mammals waded back into the water, presumably to feed on the abundant plant and animal forms there. These pig-sized, four-legged, warm-blooded, placental creatures adapted quickly to their new habitat and soon gave rise to a new branch in the evolutionary tree — the order Cetacea, which today includes all of the world’s whales, dolphins, and porpoises.
Three groups of cetaceans arose from the land-dwelling ancestor or ancestors. The earliest group, the Archaeoceti, or ancient whales, died out about 20 million years ago. Of the surviving groups, one, the Odontoceti, or toothed whales, evolved specialized teeth to grasp fish and other relatively large prey such as squid, while the other living group, the Mysticeti, or baleen whales, lost their teeth and developed very large mouths equipped with filtering fringes or baleen with which they trap large numbers of very small organisms. Both of these evolutionary paths proved to be successful, and each group has diversified to fill various niches. Although the demands of mobility, heat conservation, and sensory awareness in an aquatic environment have caused both groups to evolve superficially similar body forms, they are quite different animals.
Both primitive baleen whales and toothed whales derived from the archaeocetes, and they, in turn, had probably evolved millions of years earlier in the Paleocene or Lower Miocene epoch from a group of small, generalized, carnivorous land mammals called creodonts. The earliest and most primitive cetacean fossil yet found, Pakicetus inachus, dates from the early Eocene epoch (about 60 million years ago) of Pakistan; it seems to have been an amphibious creature preying on fish in the shallow waters of the ancient eastern Tethys Sea.
THE TOOTHED WHALES
The Odontoceti, or toothed whales (from the Greek: odontos – tooth; ketos – whale), is comprised of 72 generally recognized species that include dolphins and porpoises as well as the giant sperm whale made famous by Herman Melville’s Moby Dick, and other whales of intermediate size. All of these whales are characterized by one external nostril, or blowhole, as well as teeth. Toothed whales typically use their teeth to seize prey such as squid, shrimp, fish, or other creatures which are then swallowed whole. With few exceptions, whales generally do not tear apart or chew their food.
Among the toothed whales, several families – close related groups of species – have evolved, each with distinct behavior and geographic distribution. Each of these families will be discussed at greater length in the chapters you can access on this site, but briefly they are:
• Physeteridae: Large, deep-diving, gregarious sperm whales – and dwarf and pygmy sperm whales – with a protruding forehead and numerous conical teeth that erupt and are functional only in the lower jaw only.
• Ziphiidae: Medium-sized, deep-diving whales whose snouts are elongated, giving them a “beaked” appearance – having, with one exception, a few peg-like teeth (usually two) which erupt in the lower jaw only and are apparently not functional in feeding. The exception, Shepherd’s beaked whale, has numerous small, conical teeth in addition to two large teeth that erupt in males.
• Delphinidae: True dolphins, small to medium-sized, including some called “whales” with many functional interlocking conical teeth in the upper and lower jaw. These dolphins are adapted to a marine habitat.
• Monodontidae: Medium-sized whales with relatively few teeth, generally nonfunctional in feeding. There are only two species, both adapted to Arctic marine waters. In one of these, the narwhal, a single highly specialized tooth forms a long spiral tusk.
• Platanistidae: Small dolphins with a long, slender snout, with many functional interlocking, conical teeth in the upper and lower jaws. For the most part, these dolphins have become adapted to freshwater and estuarine habitats.
• Phocoenidae: Porpoises with an inflexible neck and small, spade-shaped teeth. Their distribution is entirely marine, with a tendency toward inshore rather than pelagic (offshore) waters.
In their habitats, the toothed whales have developed along three principal lines of distribution and prey selection. Some are oceanic deep divers that feed upon bottom-dwelling species; others are oceanic but feed on prey species living at or near the surface of the sea. Still others occupy the productive inshore habitats.
The first group includes the giant sperm whale, which is capable of hour-long dives at depths exceeding one mile (1.5 k), and the two smaller species of sperm whale; the Ziphiidae, or beaked whales, which are generally found in areas of water depths greater than one mile (1.5 k), particularly near the edges of major ocean currents and deep sea escarpments; and some species of Delphinidae, notably in the genera Globicephala and Grampus. These oceanic creatures occasionally venture into shallow waters in their search for prey, and they may drift inshore with ocean currents, but are maladapted to cope with shallows and shorelines and may become disoriented and strand themselves.
The oceanic near-surface feeders are characterized by the dolphins such as those in the genera Stenella, Delphinus, and Lagenorhynchus. These are gregarious animals that often travel in herds of up to several thousand individuals. Their distribution is worldwide in temperate and tropical seas, with Delphinus venturing in large numbers into the Mediterranean Sea, the Black Sea, and the Gulf of California. These oceanic near-surface feeders generally eat squid and fish associated with the deep scattering layers (DSL), often by night as the prey species rises to within the first three hundred-plus feet (100 meters) or so of the sea’s surface.
Inshore feeders are represented by the bottlenose dolphin and the harbor porpoise which may be found as close inshore as the surf zone, as well as in many of the busiest harbors on the world. The smaller harbor porpoise is very shy and secretive in its habits, while the friendly and curious bottlenose dolphin frequently announces its presence by splashing and sporting in bow-waves of vessels under way. These inshore species feed upon schooling fish, such as herring and mullet, and a great variety of invertebrates and near-bottom species.
In addition to these offshore/inshore and deep-water/shallow-water distinctions, whole species’ distribution patterns may be dictated by water temperature, most probably as temperature determines the distribution of less mobile prey species. While the vast majority of the toothed whales inhabit the world’s temperate seas — perhaps moving slightly toward colder regions to feed and warmer ones to breed – a few toothed whales have adapted entirely to freezing arctic waters, some others to warm tropical seas.
Wherever they may live and feed, all toothed whales share a sonar-like ability to examine their surroundings and find prey by echolocation. While most terrestrial mammals depend largely on vision for awareness of their environment, marine mammals live with the scarcity of light. The whales’ ancestors, who probably saw quite well in the air, necessarily adapted to the poor visibility typical of underwater environments.
Hearing, however, is not impaired underwater as sight is. On the contrary, it is enhanced because water transmits the pressure waves of sound much more rapidly and effectively than does air, even for extreme distances and depths. Accordingly, the toothed whales, like bats, have developed means by which they emit special sounds that travel out from their heads and reflect off objects around them, producing echoes they can hear and interpret. In this fashion they locate objects, including prey, in their vicinity, and perceive instantaneously the range, bearing, and configuration of each. Some dolphins, tested in aquarium conditions, were able to distinguish a fish they like to eat from one they did not, solely by echolocation, even though the two fish were identical in size and shape. Presumably, the dolphins determined the texture or internal structure of the two fish by echolocation. In other tests, dolphins have been able to distinguish between objects the approximate size of a B-B shot and a kernel of corn at a distance equivalent to 50 paces. Their acoustic discrimination is superb! At ease with their acoustic abilities, blind or blindfolded, dolphins will move about freely and feed normally, but a deaf or deafened dolphin will become frightened, disoriented, and reluctant to move.
We humans usually consider that only we can think conceptually and make use of sophisticated linguistic constructs for communication. Animal communication, if we assume that animals can communicate at all, is generally believed to be inferior. Our assumption of superiority in this regard may be unwarranted. In addition to finding food and resolving exquisite detail in their surroundings by echolocation, many toothed whales have obviously developed the ability to communicate with one another using whistles, clicks, and calls of various sorts. No one really knows if they say anything, much less whether they are capable of abstract thinking. It is certain, however, that they do communicate, and they often coordinate very complex group activities by such communication.
Nevertheless, sophisticated acoustic skills, ability to communicate, and a large and well-developed brain do not prove that cetacean intelligence is equal or superior to that of human beings as some investigators have suggested. Both humans and cetaceans have evolved in different ways, adapting to very different conditions, and it is we who define intelligence in such a way as to exclude other animals. Marvelous cetacean “intelligence” may one day be proven, but that will not be until we can understand their communication. Until then we must be patient. Modern explorations into interspecies communication have just begun and the results of such explorations must be evaluated carefully. After all, human beings have developed a sonar capacity through the use of machines only in the past few decades, while Odontocetes have been refining their acoustic apparatus for about 50 million years. It should come as no surprise that they are spectacularly proficient with it — more so then we by far.
Beyond echolocation, the ancestors of the Odontocetes needed other adaptations to be successful in the marine environment. They needed mobility and agility in the water, and the capacity to make long, deep dives. The earliest cetaceans quickly became streamlined, losing their drag-producing hair and evolving a spindle-shaped body. To stay warm, they developed a blubber layer and improved their circulatory thermoregulation mechanisms. They also developed great sensitivity and control over their entire skin and their appendages, which evolved from legs, paws, and tails into paddle-shaped fins and flukes. Their nostrils migrated from the front of the face to the top of the head, where breathing could be accomplished with little or no hindrance to forward motion. And their respiratory physiology and internal anatomy changed, ultimately making possible – for some species at least — dives of astonishing depths and duration.
THE BALEEN WHALES
An adaptation no less successful than that of the toothed whales was the accomplishment by the second major group of cetaceans, the Mysticeti (from the Greek: mystax: moustache; ketos: whale). Instead of seizing one or two moderate-sized prey at a time, the Mysticeti, or baleen whales, consume enormous numbers of very small prey with every mouthful. The tremendous blooms of invertebrate organisms and small schooling fish that occur seasonally in various regions of the sea provide an ideal albeit episodic food supply for those creatures that can get to them first and eat the most. In response to these blooms, baleen whale evolution has been characterized by migrations to and from the feeding grounds – often journeys of thousands of miles – and development of sievelike food-gathering structures – baleen plates — in place of teeth.
These baleen plates or baleens are akin to the epidermal ridges on the roof of the human mouth but have a texture somewhat similar to fingernail tissue, and they grow to considerable lengths (see chart). While the actual number of baleen plates in the mouth varies from one species to another, and one individual to another, ordinarily there are several hundred. Each is tapered with a bristly fringe facing inward, and a straight slat-like edge facing outward The plates are spaced a little less than 1/4″ (1 cm) apart (the precise spacing also varies from species to species and individual to individual) with the results that the complete set of baleen plates somewhat resembles a palm frond attached along its entire length to the whale’s upper gum. In addition to baleen plates, these whales are characterized by two external nostrils, or blowholes.
The manner in which baleen whales feed varies with the species of whale and prey, and sometimes with individual style. All, however, dine very efficiently on the small organisms near the lower levels of the food chain. The various species of baleen whales have become specialized according to the habitats and habits of their prey. Some, such as the right whale, have very finely fringed baleen, with which they can filter and consume very small planktonic organisms simply by skimming open mouthed through the water. In this manner a right whale can filter thousands of cubic feet of seawater and extract from it approximately two tons (1,700 kg) of nearly microscopic plankton per day.
Other whales, such as the fin and the blue, have more coarsely fringed baleen, and feed upon correspondingly larger, often active pray that swarm in dense schools. To catch the shrimp-like crustaceans and small schooling fish that are staple items in their diets, these whales must swim rapidly and with enough agility to herd a school into a tight mass, and then grab as many individuals as possible with a single, lunging gulp. These whales have longitudinal pleats of skin extending from the chin to the chest or belly region making the whale’s throat enormously expandable, like a pelican’s throat pouch. A large whale’s distensible throat permits it to trap thousands of gallons of food and water with each mouthful. The whale’s belly and jaw muscles then contract to force the water out between the baleen plates, leaving bushels of tiny prey in the whale’s mouth. In this way the largest species may filter many thousands of cubic feet of water and consume about four ton (3,600 kg) of food per day.
The gray whale employs a feeding style that differs from that of any other whale. The gray is the most “primitive” of all whales in appearance, and its feeding habits are presumably similar to those of the ancestors of all baleen whales. Gray whales typically feed on small fish and invertebrates found in or near the bottom sediments in shallow waters. Some observations have been made which suggest that the whale’s tongue acts as a hydraulic piston in the mouth. Apparently, the whale swims on its side near the ocean floor and pushes water out of its mouth through its baleen plates and lower gums, stirring up the bottom sediments and the organisms living in or near it are drawn into its mouth. As the whale rises to the surface, it may sluice its mouth with clean water and swallow its catch, sometimes gaining a gravity assist by sticking its head vertically out of the water. The sluicing portion of the maneuver may be omitted in order to suck creatures from the bottom. The method of feeding on bottom species is popularly known as “grubbing”.
Evidence offered in support of this picture of the gray whale’s feeding habits include the fact that many gray whales taken by whalers have been found with rocks, sticks, seaweed, and a great variety of shallow-water, bottom-dwelling species in their stomachs. Also, there have been direct observations of suction feeding upon invertebrates by a young gray whale in captivity and indirect evidence from trough-like depressions in bottom sediments where gray whales have been feeding.Apparently, gray whales have little competition for their food supplies and this may have contributed to their recovering twice from near extinction due to whaling in the past century. Now they thrive again in the inshore waters of their ancestors.The world’s seas cover 71 percent of the planet’s surface, or roughly 140 million square miles (370 million square kilometers). Their total volume is about 350 million cubic miles (1.5 billion cubic kilometers), their average depth 2.5 miles (4 kilometers). Most of the radiated energy that falls on the earth from the sun falls upon the sea, heating its surface waters and providing light for the photosynthetic organisms that exist there at the primary level of a food chain leading up to the whales and other marine mammals. In the sea as on land, the changes of season affect the amount of food available in any particular region. Temperature differences between water masses in different parts of the sea create imbalances in the air and water resulting in the patterns of oceanic currents that dominate the weather both at sea and on land.
While the marine environment changes continually in some respects, it is very stable in others; as a swimming medium it provides continuous physical support; it resists rapid chance in temperature; it is fairly uniformly saline; and it contains, dissolved within it, all the trace elements necessary to life as well as essential gasses such as oxygen and carbon dioxide.
Water weighs about 62.4 pounds per cubic foot (one gram per cubic centimeter) and is virtually incompressible; the pressure on any organism in the water, therefore, increases with depth. Increased pressure presents little problem for fish and invertebrates such as squid, or for plants, which have no air sacs within them. But for a whale, or for any other creature that takes air into its lungs at the surface, pressure becomes a critical factor that must be dealt with if the animal is to penetrate very far beneath the surface.
The air we breathe is composed of approximately 80 percent nitrogen and 20 percent oxygen, and atmospheric pressure at sea level is about 14.7 pounds per square inch (2,300 newtons per square meter). We know that human divers may suffer the bends (nitrogen bubbles forming in the blood and other body fluids) if they fail to ventilate and decompress adequately when returning from dives to depths at which the pressure is equal to as little as twice the atmospheric pressure at sea level — 64 feet (20 meters). They may also suffer nitrogen narcosis, the condition known as “raptures of the deep” in which nitrogen in nerve membranes under pressure can lead to progressive disruption of central nervous systems functions, followed by disorientation and unconsciousness. At depth, a single lungful of surface air contains enough nitrogen to bring on the effects of narcosis. The problem of raptures is compounded for divers using self-contained underwater breathing apparatus (SCUBA) gear: because the air itself is breathed under pressure, more molecules of nitrogen are taken in with each lungful. For this reason, divers working at depths greater than 160 feet (50 meters) often use a helium-oxygen mixture for breathing, rather than ordinary compressed air, because helium does not produce the rapture effects.
The problems of pressure and nitrogen notwithstanding, some cetaceans are capable of prolonged dives to depths as great as a mile (1,500 meters), where pressure on their bodies exceeds 2,600 pounds per square inch (7.7 million newtons per square meter), or about 180 times the atmospheric pressure at sea level. Researchers are still investigating the methods by which whales have solved the problems inherent in mammalian diving. Although they have not yet answered the central questions, they have discovered many surprising adaptive features of these animals’ anatomy and physiology.
For example, they have found that whales’ lungs collapse at great depths, as would be expected, but their ribs do not break, as human ribs would, because the cetacean rib cage is less rigid than that of land mammals. They have found that whale blood has a higher percentage of fats with an affinity for nitrogen that reduce the quantity of dissolved nitrogen available to nerve membranes in a whale’s blood. It is even supposed that excess nitrogen in the airways may be eliminated with a phlegm of fat droplets in the expired air when a whale surfaces and “spouts”. Those who have photographed whales can attest to the existence of this phlegm after particularly close encounters with whale breath, when they have had to wipe the oily mist from camera lenses.
To obtain enough oxygen to remain at depth for a long period, a whale fills its lungs to about 90 percent of their total capacity with each breath, compared with about 20 percent among terrestrial mammals. Although they do not have proportionately larger lungs than land mammals, whales do have more blood in proportion to their total body weight, and more hemoglobin (an oxygen-carrying substance) in their blood which allows more oxygen to be taken from each breath. Whale blood chemistry permits a more efficient net transfer of oxygen to tissue at any pressure than that of land mammals by being slightly more acidic. Aside from blood, whale muscle tissue is rich in myoglobin, a substance similar to hemoglobin in its oxygen-binding properties. Myoglobin stores oxygen in a whale’s muscles, making it available for work on demand in the absence of an oxygenated blood supply.
Additionally, whale body tissue easily adapts to anaerobic (without oxygen) metabolism for short periods of time, with the result that whales have a wider tolerance for the consequences of oxygen deprivation than do their counterparts on land.In addition to being anatomically adapted to withstand great pressure, a marine mammal must maintain its body temperature in the chilling waters of the seas, where temperatures may be as much as 60 degrees Fahrenheit (16 degrees Celsius) lower than the animal’s own temperature. To overcome this, all whales have developed an insulating layer of blubber (fat which may be a foot, or a third of a meter, thick), and have evolved the basic torpedo or spindle shape with small appendages to reduce the ratio of surface are to body volume (body heat is produced in proportion to body volume, but is dissipated in proportion to body surface area). Whales also have developed to an exquisite degree a counter-current heat exchange system of arteries and veins to and from their fins, flukes, and flippers. This system allows the warm arterial blood pulsing out from the whale’s body core to relinquish its heat to a surrounding network of incoming veins in each appendage, so that heat loss to the surrounding water is greatly reduced. When a whale is overheated from exertion, for example, the effect of the system can be reversed, so that heat from the whale is given up to the water, thus cooling the animal.
OTHER NECESSARY ADAPTATIONS
Animal tissue is approximately the same density as seawater. Therefore, when the whales’ ancestors returned to the sea, the water supported them so that they no longer needed structural support of heavy bones and feel planted firmly on the ground. As the mammals adapted to their watery environment their bony structures became important principally as a frame for attachment of propulsive muscles: the vertebral column was compressed in the neck and chest area while it expanded toward the tail, providing effective leverage for the propelling flukes that swept up and down through the water; and the front legs evolved to become paddles, or flippers, which controlled water flow and steering.
The supportive properties of water also freed whales from gravitational and structural restraints on their size, although, of course not all became leviathans. A huge terrestrial mammal such as the elephant must support its ponderous weight on thick, stumpy legs, while the blue whale — heavier than 20 elephants — is buoyed easily and gracefully by the sea.
Although constrained by heredity and the efficiency of size in catching prey, a whale is not limited structurally to any size. In large measure, each species will evolve to a particular size in response to the food supplies available to its lineage, limiting its size. As the large whales evolved to feed efficiently upon large quantities of seasonally abundant swarms of small prey in the open sea, small whales and dolphins evolved to feed upon smaller numbers of larger, individual prey animals. The smallest porpoise can catch single fish efficiently in shallow inshore waters, where a large whale could not survive. Conversely, large whales can harvest the enormous seasonal zooplankton “crops” of the open sea more efficiently.
Along with the rest of the mammalian body, whale skin has evolved in response to its watery environment. As already mentioned, whales have lost virtually all of their drag-producing hair, and developed smooth, rubbery skin which ripples elastically as water flows along the surface. This unique ability permits a whale to attain greater speeds than a comparably sized rigid structure might reach with equal propulsion power — a feature that has attracted the experimental interest of many naval architects.
All creatures must be able to locate others of their kind in order to reproduce. Many are gregarious, as well, living in groups to feed, for protection, perhaps just for company. But, in the enormity of the sea, individuals of a species might lose each other entirely had they no active ability to communicate beyond the scant limits of vision and no social order to keep them together. The dimensions of the sea forced whales along evolutionary paths that ensured group cohesiveness: to a greater of lesser extent, all species of whales communicate, and all form social groups for at least part of their life cycle.
The astonishing acoustic talents of whales have been mentioned, but it is important to emphasize that they developed in response to the physical demands of the water environment. Below about 500 feet (150 meters), darkness prevails in the sea, and above that depth vision is very limited in almost all waters. Echolocation of objects at distances far beyond the limits of vision is possible because sound travels very efficiently in seawater, and does so at about five times the speed of sound in air. The acoustic situation is not simple, however. Sound waves bend or refract when they pass through the boundaries of layers of water caused by differences in temperature, pressure, or salinity. Temperature and pressure change with depth in the ocean, and salinity may vary from place to place as well as layer to layer, so refraction must be dealt with in echolocation is to function well. Also, if either the target (prey) or the echolocation is moving, shifts in the frequencies of the echos will be caused by what is known as the Doppler effect. These shifts can yield precise information about relative speed and orientation of objects in three dimensions, if they can be interpreted.
Certainly the effective use of sound by whales suggests that they possess exquisite working awareness of the physics of sound in water. Their loquaciousness in social context suggests, in addition, a communicative ability that in some ways may be better than our own, at least in potential “bits” of information communicated and the speed of their transmission. Probably the bulk of the cetacean brain is devoted to the rapid assimilation and mental solution of these physics problems. Computer tests of cetacean abilities to discriminate signals and communicate are only now being attempted, and the results are eagerly awaited. In an almost longing way, we humans want to find higher meaning in cetacean sounds, but we must not let ourselves give them human meanings in human contexts.
COMMON WHALE BEHAVIORS
Most whales see quite well in air, a carry-over from their ancestors’ land-dwelling days. Whenever a whale wants to see objects on nearby land or in boats, it simply raises its head above the water and looks. This maneuver, called “spy-hopping” may allow a whale to scrutinize objects of concern, investigate disturbances such as passing ships and other noisy machinery that invade its acoustic senses, or it may permit it to navigate by coastlines. Whales seem to spy-hop for other reasons as well. Gray whales, for instance, may raise their head above the water to get a gravitational assist when swallowing a mouthful of bottom organisms or debris. Often they do not even raise the eye above water, in which case it certainly is unlikely they are looking around.
Whales may also leap partly or completely out of the water — an activity called “breaching”. Breaching may allow an animal an excellent airborne view (if it opens its eyes), it may serve to shake off small parasites clinging to the skin, or the loud splash may serve as some sort of signal to other whales. Or, maybe, it is simply fun and good exercise to jump and make a big splash. Humpback whale calves, for example, seem to breach as a form of play or as an indication of excitement.
Whales also splash the water with their fins and flukes, activities called, respectively, “finning” or “flippering” and “lobtailing”. In these maneuvers the animal strikes its appendages flat against the water, producing a noise that can be heard for great distances on a calm day. Lobtailing and finning may play a role in feeding. Groups of dolphins and killer whales have been known to fin and lobtail when herding prey species. Sometimes part of a group will lobtail and splash while the others feed; the roles are then reversed, giving all members of the group an opportunity to feed. Evidently, prey species’ freedom to move and escape capture in the sea has encouraged social coordination and organization among their cetacean predators.
Some cetacean social activity appears to be directed toward purposes other than feeding, for example, mating and rearing of young. For both activities the details of social structure vary with the species. Whales of a number of species are known to take many mates during their lifetimes. Some may take only one, but none have been proven to be strictly monogamous in spite of popular stories to the contrary.
Many whale species have never been observed in courtship and mating activities. However, in mating, all cetaceans face the same general problems. Without arms to grasp and hold tight to one another in the rolling seas, cetacean copulation could be difficult and clumsy had nature noy provided the male with a penis that is essentially prehensile. It is strongly tapered toward the end and has the ability to roll and flex at the tip, permitting it to maneuver itself across the female’s blubbery skin until it locates the vagina. It is also a very substantial structure, built to withstand the enormous torque created by the sweeping flukes and rolling bodies of the mating couple.
In some species, such as the gray whale, sexual efforts may be assisted (or perhaps interfered with) by a second (or even a third or fourth) male who may push against the female to help the other male or perhaps to increase the second individual’s own chances of coitus if the female has no escape and submits. Dolphins usually accomplish their copulation without such “assistance”, and they may repeat coitus frequently for days, months, or even years. In fact, from observing them in captivity one might wonder if they ever do much else. Even in the wild, there is frequent sexual activity between many members of a herd, with no apparent taboos concerning the relationship (sometimes even the species) of the participants. Much of the sexual activity has no reproductive significance, as it occurs whether or not the females are in oestrus or breeding condition. This suggests that, as in primates, sexual activity may be important in social bonding of herdmates and group members.
As with mating, details concerning the rearing of offspring are lacking for many species. The young of some species accompany their mothers for only six months to a year while they nurse; others receive parental care and guidance for many years after weaning. Many species of whales seem to exhibit great tenderness and concern for their young. Some species are legendary for the ferocity with which they defend their young, even in the face of such overwhelming danger as that presented by whalers. Perhaps it is this sense of parental care, of responsibility, almost, together with their apparent intelligence, curiosity, and inoffensiveness of whales that has always drawn us to them.