(part 2)
Even though dependent pups usually captured the same prey species as their mothers, they were much less successful at
obtaining food. Apparently, it takes a long time to learn the difficult and complex skills of foraging in Monterey, where
otters have lived for many years and populations of otter prey are somewhat reduced. Pups captured real food on only 13
percent of their dives, whereas mothers captured prey on 70 percent of their dives. Almost ten percent of a pup's dives
resulted in the capture of a non-prey item. Such "prey" was often tasted repeatedly or pounded unsuccessfully.


Josie provides an example here as well. One day several years ago, when Josie was a large pup, she foraged in the harbor with
her mother. As she surfaced from one dive, I could see she was struggling to bring something to the surface. It was an old
automobile tire, bigger than she was. I'd seen pups capture all sorts of "junk food," including aluminum cans, driftwood,
pine cones, plastic bags, even golf balls, but this was a first. Josie chewed on the tire for a minute, as though it was the
most natural food in the world, then let it sink to the bottom. Meanwhile, munching on a rock oyster, her mother watched,
apparently unconcerned, as her pup retrieved the tire once more and wrestled it to the surface.




While watching Josie and her mother, I often heard the pup squeal with the ear-splitting scream emitted by distressed or
hungry pups, especially when they are separated or hungry. Sometimes Female 190 responded with her own piercing call.
Analysis of the vocalizations of mothers and pups have shown that each one has a very distinctive "scream," which probably
helps the mother and pup stay in contact. Even the human ear can detect differences. One female's call always sounded like a
raspy, quacking duck to me.


We identified at least ten types of sea otter vocalizations: screams, whines, whistles, squeals, whimpers, squeaks, hisses,
growls, coos, and grunts. The sea otter's vocal patterns seem to be most suitable for short-range communication among
familiar individuals, Many of their sounds are often quite soft and difficult to hear from shore. The soothing coo, for
instance, is even made with the mouth closed. It occurs between mothers and pups and between pair-bonded adults during
courtship, but otters may also coo while eating.


Sea otters also appear to communicate through scent and with ritualized nuzzling and "head-jerk" interactions. Nuzzling
involves a gentle rubbing with the nose, but for the exaggerated head-jerk, an otter buries its nose in another otter's fur
and shakes its head from side-to-side in a series of rapid jerks. A sea otter that is entering, leaving, or simply swimming
past a raft of otters will typically approach and make contact in this way with some or all of the animals in the group. I
suspect that sea otters can easily recognize other individuals, and even preferentially interact with certain otters.




Only a handful of animals, including some birds, insects, dolphins, primates, and, of course, humans, have the ability to use
tools. Sea otters are members of this select group. While floating face up on the surface, an otter often places a flat rock
on its chest as an anvil and pounds mollusks against it until the tough outer shell breaks open. From my observations, this
technique accounts for over half of an otter's tool use. Sometimes a second rock serves as a hammer to crush the shell
against the rock anvil. Otters also bring rocks underwater to pry loose stubborn abalone or urchins tightly wedged in
crevices.


Just as with their varied diets, sea otters have devised an astonishing array of innovative methods to capture, secure, and
break open prey using many different kinds of tools. Adult otters are known to employ over 30 different tool-use techniques
and use at least 14 different types of tools, including rocks, large cement slabs, glass bottles, crab claws, shells, kelp,
wood, and bricks. Many otters always use the same kind of tool or have distinctive ways of using their tools.


For instance, during all the years I studied her, when she was feeding, Female 182, or Flatstoner, carried a huge flat rock
or a concrete slab found along Cannery Row. Underwater, she used this massive tool to bash off abalone stuck tightly to
rocks. On the surface she placed the rock or slab across her chest like a "table" as she ate.


Flatstoner didn't always rely on her rock, however. Sometimes she and her "neighbor" Whitehead fed on mussels in the same
spot, but each female had her own way of opening them. Flatstoner grabbed clumps of mussels from shoreline rocks and ripped
them open with her teeth. Whitehead dove underwater to capture her mussels, then dove again to find a rock, which she used to
crack the mussel shells.


Otters are able to vary their method of tool use in relation to specific types of prey, one of the only examples of such
flexible tool-using behavior among non primates. One female who simultaneously captured both a purple urchin and turban
snails first ate the purple urchin by cracking it apart with her teeth. Before consuming the snails, she made a dive,
apparently to obtain a rock to break open the hard-shelled snails.


Although there is considerable individual variation in the proportion of time a tool is used to capture a particular type of
prey, tools tend to be used much more frequently for certain prey types than for others. For example, a tool is used about 95
percent of the time with turban snails, 47 percent of the time with rock oysters and rock scallops (Hinnites spp.), 15
percent of the time with purple urchins, and rarely, if ever, with fat innkeeper worms, squid (Loligo opalescens), octopus,
and sea stars (Pisaster spp.).


Besides using tools to capture prey, sea otters employ other tactics for preventing their escape. An otter fortunate enough
to capture two or more large crabs at once has to subdue the struggling crustaceans before they get away. To keep the second
crab from escaping or pinching while the first one is being eaten, the otter wraps kelp tightly around the crab until it
looks like a mummy. We called this strategy "straitjacketing." Female 535 had learned to straitjacket large rock crabs by the
time she was ten months old. Sometimes she used surf grass instead of kelp for a restraint. Another maneuver to prevent crabs
from escaping is the "hindflipper crab block," in which the otter imprisons its catch by folding its hindflippers tightly
over the crab.


After capturing a sea urchin, an otter often employs a tactic we called "urchin rolling." To break off the urchin's spines
before eating it, the otter, using the pads of both paws, rapidly spins the prickly sea urchin, like rolling balls of play
dough. Sometimes the otter turns the urchin over and taps a spot on its bottom, causing the urchin to flatten its spines.


The "sea star stick" is made when an otter folds a sea star's arms down and inward so the sticky tube feet adhere to each
other. This otter can then concentrate on consuming the sea star without it constantly sticking to the otter's fur. This
technique proves especially useful for eating a giant sunflower star (Pycnopodia helianthoides), which has up to 15 long,
sticky arms.


In "mollusk squishing," an otter that has captured a small clam or other mollusk rotates the shell and, at the same time,
pushes it with its powerful forelegs. This push-and-twist motion usually pops open the clam. Another method of opening clams
is called "siphon striping." Clams have two long tubes of flesh peeking out of the shell, called siphons, which suck in tiny
food particles and push out waste. To open tightly clamped clam shells, some otters grab the siphon with their teeth and
remove it with a quick jerk. One otter, Female 532, even came up with an unusual technique to eat abalone: she used a piece
of abalone shell as a "spoon" to scoop out the abalone meat.


A quick and easy way of collecting many turban snails at once, called the "snail shake," was a technique that Nosebuster and
other snail-eaters use a lot. Twisting and wriggling just beneath the surface of the kelp canopy, the otter sends scores of
snails falling off the kelp plant into its paws, like ripe fruit shaken from a tree. As the otter collects the snails, it
stores them in a pouch of loose skin under its forelegs. Later the feeder will reach into its "armpit purse" and snack on the
snails.


In another example of an otter outwitting its prey, one young male learned that small octopuses sometimes hide in discarded
"pop-top" beverage cans which litter the bottom of Monterey Harbor. After "capturing" a suspiciously heavy can, this
enterprising male would bite it open and make a meal of the octopus inside.


Some otters have developed the bad habit of looking for hand-outs from local boaters or divers. One otter learned to reach
into a squid-filled bucket on the stern of a boat docked in the harbor. And the infamous Josie joined the begging seals and
pelicans waiting for fish to be thrown by tourists. She even threatened adult male sea lions, who were many times her size,
and grabbed at fish before they could get them. this was especially unusual because California otters virtually never eat
fish. (This contrasts with sea otters in Alaska and Russia, where fish may form a staple, especially where otters have
depleted invertebrate prey while fish remain abundant.)


A few sea otters in Monterey Bay have actually learned to catch and eat seabirds--a very unusual behavior among all three
subspecies of sea otters. We saw western grebes, sea gulls, surf scoters, common loons, and cormorants all fall victim to the
stealthy bird-eaters. I couldn't help wondering if the bird-eating otters might have learned this practice by watching other
otters, since most seabird attacks occurred in the same areas.


We saw one male otter, who lived in Whaler's Cove at Point Lobos, eat at least six birds. Western grebes were his favorite,
even though they are half as big as an otter and have long, dangerously sharp beaks. This resourceful male would sneak up on
the grebe from underwater, grab the surprised bird's feet, and deliver a fatal bite to its neck or head.


Although such behavior is anomalous, seabird foraging offers yet another example of how sea otters can learn new behaviors.
The skills required to hunt, capture, subdue and consume a strong and sharp-billed grebe differ greatly from those needed to
capture slowmoving or sessile invertebrates.


Individual sea otters appear to forage more efficiently by specializing on prey. This fact may have contributed to the
evolution of their distinctive diets, and the varied feeding patterns may also lessen competition for food in areas where sea
otter populations are well established, such as around Monterey Bay. When California sea otters have lived in an area for
many years, populations of preferred prey, such as large rock crabs, abalone, and red urchins, become less abundant and the
diet of the otter population diversifies. Otters that are more efficient at processing specialized prey may have an adaptive
advantage in finding enough food to meet their high energetic needs.


Even though I've spent thousands of hours observing these remarkable mammals, their behavior never fails to surprise me, and
I feel I've only just begun to scratch the surface of what there is to learn about sea otters. As long as we continue to
protect the California sea otters, listed as "threatened" under the Endangered Species Act since 1977, they will prove to be
a delightful source of entertainment, education, and future scientific discovery.