by Janet Spencer
Come along with Tidbits as we consider the intelligence of animals!
LEARNED OR INHERENT?
• Researchers raised baby weaver finches without ever giving them access to weaving materials or letting them watch adult weaver birds construct nests. When they were then given weaving materials, only 26% were able to build a functional nest. This evidence went a long way towards proving that nest-building is not an innate trait, but must be learned from watching elders, and practicing.
• Two species of field mice were involved in a study. One builds a simple underground burrow leading to a single chamber. The other builds an underground burrow leading to several different chambers. Researchers deprived a set of test mice of any opportunity to dig a burrow for 20 generations of mice. Then they gave both species of mice access to dirt to dig in. What sort of burrows would they build? They built exactly the sort of burrows that previous generations had constructed. There was no change whatsoever. The scientists concluded that burrow-building was inherited, written in their DNA.
• A tiny orb web spiderling can build an orb web without ever seeing anyone else build an orb web, and does not need to practice to perfect the art.
• A predatory bug feeds on termites whenever they rise to the surface of their mound to repair it. One species of this bug has learned to capture a termite, suck it dry, and then use the empty husk as a disguise, creeping back to the place where the other termites are still repairing the mound. Termites always collect and discard their dead. As soon as another termite turns up to do this, it becomes the second victim, and the feast continues. It’s evidence of tool use in bugs.
• A particular species of wasp digs a burrow in the ground, lays an egg inside it, and provisions it with paralyzed insects to be the larvae’s first meals. She then closes off the burrow by filling it with tiny stones and bits of sand. When the hole is full, she grabs a stone held in her jaws to hammer down the soil over the burrow entrance. It’s another instance of tool use by insects.
• Chimps often use sticks to get termites out of termite mounds. They insert it into the mound where termites swarm over it and are then pulled out to be eaten. But some chimps use two tools: a sturdy one for breaching the wall of the mound, and a probe stick with a feathered end for collecting the most termites possible. This is an example of an animal using a tool set instead of just a tool.
• A chimp was seen using four tools to extract honey from a bee’s nest: one used as a chisel to break open the exterior wall; the second was a more delicate chisel to breach the interior wall of the hive; next, a needle-sharp stick to pierce the honey storage units; finally, a dip stick repeatedly inserted and withdrawn, dripping with honey. Another tool set.
• Bottlenose dolphins off the coast of Australia pick up sponges from coral reefs and hold them in their teeth so that the sponge covers the dolphin’s nose. It is then able to probe the ocean floor for things to eat while being well-protected from things that sting.
• In Guinea, West Africa, chimps use rocks to break open palm nuts. One rock must be flat and level to act as an anvil where the nut is placed, and it is struck with a hard rock held in the hand, with just enough force to break the shell without damaging the kernel. One chimp was recorded placing one rock underneath the anvil rock in order to make it more level, using a tool to improve a tool.
• The New Caledonian crow uses twigs as tools, and fashions them according to their purpose. One kind of tool is a narrow flexible twig that the crow has stripped of side branches and leaves, but left a spurred hook at the thicker end of the stick. The bird holds the narrow end inserts the hook into crevices to pull out grubs. The other tool is fashioned from a leaf so that one edge of the leaf has a jagged edge like a saw and is able to scrape the sides of narrow crevices to pull out smaller insects.
• The male red-headed weaver bird snips the leaves off a living twig, then snaps the twig off the tree but does not cut it all the way through. When the bird flies off with the twig clutched in its beak, it strips a long thin tongue of bark trailing from the snipped end. The bird then winds this strip of bark around a branch where it is contstructing its nest, acting as an anchor point. When the bark dries out, it becomes sturdy like leather. The bird repeats this over and over again until it has constructed a hanging chamber with the entrance on the bottom of the nest.
• Two hand-raised New Caledonian crows were placed in an aviary that contained all sorts of sticks. Their caretakers gave them many lessons demonstrating how to use sticks to retrieve food from confined spaces. Two other young crows were placed in an identical aviary with sticks, but they were not shown how to use the sticks. Nevertheless, the untrained crows learned to use the twigs without anyone ever showing them how.
• The bolas spider traps prey by dangling a long sticky line with big sticky ball at the end. It only feeds on the males of two types of moth, so catching prey using only this method would be tough. But the spider has a secret weapon: pheromones that imitate the sex signal of the female of the two moth species. One type of moth is active only during the early morning, and the other is active only in the evening, and the spider switches the scent of the bolas accordingly.
• When blindfolded college students were pitted against non-blindfolded rats in a maze-running contest, the rats outdid the students. They consistently learned the pattern of the maze in one-third the number of trips as the humans.
• When it comes to running mazes, scientists rank the following animals in order of intelligence: kitten, rat, guppy, Guinea pig, chick, turtle.
• Modern man possesses a brain of about 53 ounces or 3.3 pounds (91.5 kg), approximately 1/50th of total body weight. It can be said that every gram of brain weight is in charge of 50 grams of body. A chimpanzee’s brain is about 1/150th of body weight and the gorilla’s is 1/500th. But size isn’t everything. Two other mammals have massive brains without accompanying superintelligence: the largest elephants can have brains as huge as 13 lbs. (6 kg), while the largest whales can have 19-pound (8.6 kg) brains. Consider the enormous bodies these brains must deal with and the ratios become clearer: the elephant brain represents only 1 /1,000th of its body weight and large whales may be only 1/10,000th body weight. The best rule is to consider man’s condition: a brain that is both large in the absolute sense and large in relation to body size. (Or else hummingbirds, with a larger brain/body ratio than man, would be smarter than Einstein.)