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.Very little of it is toxic or indigestible, so learningwhat s good to eat is not a major task for a gorilla child.But many ofthe best food plants have stings, spines, hooks, or tough cases, so learn-ing how to eat these is harder.Mountain gorillas are fond of nettles,but dislike being stung.Adult gorillas pick nettle leaves and fold thestinging top and edges into the middle of a bundle before they eatthem.Gorilla children haven t figured this out yet, and get stung whenthey first start eating nettles.The only adult gorillas at Karisoke who* It is unclear whether Tara was descended from Indian tigers, as Singh writes that he wasassured.It is said that testing has shown Siberian tiger genes present in wild tigers now liv-ing in the area, a source of great displeasure for those who hope to save not only the tigerbut the different subspecies of tiger.178 BECOMING A TIGER-didn t fold their nettle leaves were a female with maimed hands and afemale named Picasso, who transferred into the area as an adult.Picasso grew up at a lower elevation, where few nettles grow.Investigators Richard and Jennifer Byrne suggest that in her youthPicasso didn t get to observe other gorillas folding nettles and so didn tlearn to do it herself.Interestingly, her son Ineza, three years old, wasnot very good at processing his nettles.The Byrnes suggest that the gorillas learn how to process difficultfoods by trial and error, but that young gorillas may be showing pro-gram-level imitation.Thus a gorilla child gets the idea to fold nettlesfrom noticing that its mother folds nettles before eating, but it doesn tprecisely copy her movements.Instead it figures out for itself how tofold nettles; as a result, each gorilla has its own idiosyncratic ways ofexecuting the same processing techniques.Thick-billed parrots eat a lot of pine nuts, which they extract frompinecones.Learning to do this takes young parrots several months.Captive-reared birds who were given pinecones for six months beforebeing released eventually learned how to get food out of them butthen when they were free, couldn t figure out where to find pinecones.Squirrels? How could it be squirrels?In the early 1980s a high school biology teacher in Israel, Ran Aisner,took students on a field trip to some plantations of Jerusalem pine.These had been planted in the last 50 years and did not constitute aparticularly natural habitat.Aisner noticed piles of pinecone scales andbare pinecone shafts under some trees on the edge of the plantationand brought them to zoologist Joseph Terkel.Clearly, Terkel said, somecreature had been stripping the scales off the cones to get at the pinenuts inside, and the culprit in such a case is generally a squirrel, butthere are no squirrels in Israel.Eventually, by placing traps in the branches of the pines, Aisnercaught some black rats.There turned out to be a population of shy ratsthat ate only pine nuts, drank only water they licked from pine nee-dles, and lived in tree nests made of pine needles.Through surreptitious observation it was discovered that the ratsselected a ripe cone, gnawed it off the branch, carried it to a better spotHow to Make a Living 179-for a sustained bout of gnawing, and took it apart in a quick and system-atic manner.This technique involves starting at the base of the cone andpulling the scales off in a manner that entails a minimum of gnawing.The scales wind around the shaft of the cone in a spiral, and the efficientthing to do is to take them off in a spiral path.After a few turns a fewrows of scales the rat will find a pine nut under each scale.The bits fallto the forest floor, potentially alerting sharp-eyed nature buffs.In Terkel s laboratory they began to investigate these rats and theirmethods.Rats of the same species who were trapped in urban sites suchas warehouses were clueless about cones and not interested in obtainingclues.If they were really hungry, and there was nothing else in the cage,they would eventually chew on the cones, but their method was simplyto start gnawing inward from a random point, a procedure so inefficientthat they would have starved had the researchers not eventually giventhem rat chow.Not one developed the spiral technique.If the city rats were housed with a rat from the piney woods whoknew how to strip cones, that didn t help.After three months of bunk-ing with an expert, they still had no inkling how it was done.Unsurprisingly, rat pups who grew up with mothers who got theirpine nuts by stripping pinecones with the spiral technique also strippedcones with the spiral technique.Of 33 rat pups raised this way in the lab-oratory, 31 could do it.Two could not and gnawed at random.The helpful researchers then provided a set of clues to adult ratswho could not imagine how to strip cones.They gave them pineconesthat had been started.The first four rows of scales had been strippedoff, so a rat that proceeded to remove scales in a spiral manner wouldfind a pine nut under each one.Of 51 grown rats, 35 could finish thejob on a started cone, using the spiral method.Twenty of these rats then received further tuition.Having suc-ceeded in doing this with cones that had had four rows removed, theywere then given cones with three rows removed, and if they succeededwith those they got cones with two rows removed, and so forth.Finallythey got intact cones.At the end of the course all of the rats couldopen cones that had had just one row removed, and 18 passed the finalexam.They could open an intact pinecone and extract all the seedswith the spiral technique.How this whole thing got started is unknown.There might have180 BECOMING A TIGER-been an innovative female rat who came up with the technique andpassed it on.(An innovative male who came up with the techniquewould not have had a chance to pass it on.) Or perhaps there was afemale who ate some pine nuts and some other foods (since withoutgood technique a rat cannot get enough pine nuts to survive) and wholeft partly eaten pinecones around, and this was sufficiently illustrativeto let the pups figure it out.More techniquesSea otters are famous for their use of rocks to smash shellfish.In thecanonical example, a sea otter floating photogenically on its backplaces a flattish rock on its chest, holds a clam in its paws, and smashesthe clam on the rock.When an otter has found a good rock, it willcarry it around in the web of loose skin under its forearm (the term pawpit is tempting, but not quite right).An otter may keep track ofa really good rock for years.Sometimes a second rock is used to ham-mer the hapless shellfish.Underwater, otters also use rocks or other objects as tools to pry orbash abalone and sea urchins loose from rocks.If they catch more thanone crab, otters will wrap the ones they aren t eating in strands of sea-weed to keep them from getting away while they eat the first one.InMonterey Bay, Female 532 was seen using a piece of abalone shell toscoop abalone meat out of its shell.Pups stay with their mothers for six months or more, getting muchof their food from their mothers and improving their skills.In onestudy the pups came up with food on 13 percent of their dives, whiletheir mothers got food on 70 percent.Pups aren t initially sure whatthings are food.Marianne Riedman describes a pup named Josieindustriously propelling an old car tire to the surface and giving it aserious chewing before deciding that it wasn t food.Female 190 passed on her liking for rock oysters to her daughtersJosie and Tubehead [ Pobierz całość w formacie PDF ]