Birds are intelligent, especially parrots and crow relatives – jays, nutcrackers, ravens, jackdaws and others. The Clark’s Nutcracker stores conifer seeds in the late summer and fall of each year and retrieves them in the winter and spring. A bird must find more than a thousand seed caches each year. The Caledonian Crow learns how to modify sticks so it can pry its favorite food of grubs out of their hiding places. In Japan, the Large-billed Crow drops hard-shelled nuts into city traffic to be crushed by cars, but waits until a red traffic light appears to retrieve the nutmeat. As I’ve noted in an earlier blog, pigeons are no dummies either.
Researchers Clayton and Dickerson wondered if California Scrub Jays have episodic memory (unique memory of a specific event). They took captive birds and allowed them to cache peanuts (a long-lasting food) and mealworms (a perishable food). The researchers prevented the birds from retrieving the food until some time had passed. If a short time had passed, the jays went after the perishable mealworms; after a longer time the birds searched for peanuts. So the jays have to remember where they put which food and understand that mealworms go bad after a short time. And they might have 200 caches. Can you remember the last 200 times you ate out?
According to some researchers, crows and allies (Corvidae) are as smart as primates in many ways. But since bird brains are much smaller, how did that happen? Well, it turns out that the Corvidae and parrots have a higher concentration of neurons in the brain than do similar-sized mammals, as many neurons as small monkeys, in fact. And these neurons are concentrated in the forebrain, the area responsible for complex behavior. So, ounce for ounce, birds have more brainpower than mammals.
That’s not all. Flying birds and bats have smaller genomes than their non-flying relatives. (I’ll not go into that explanation here; you can read an abstract of Dynamics of genome size evolution in birds and mammals if you wish.) What’s important is that smaller genome size is related to smaller cell size. That’s important to flying birds which need a high metabolism to transfer nutrients and oxygen and waste products across cells; smaller cells have a greater surface-to-volume ratio than larger cells and transfer is faster. Since there is a greater concentration of neurons in the brain and the neuronal cells are smaller, information processing can happen faster, allowing the birds to develop intelligent behaviors.
What prompted this blog is my reading The Ascent of Birds by John Reilly and Part 19, The Crow’s Story. A fascinating reading of 27 bird stories even though I had to work at it. The book is divided into self-contained chapters that encompass the evolution of modern birds from their origins in Gondwana, over 100 million years ago, to today. The stories are arranged in chronological order and describe the many dispersal and speciation events that underpin the world’s 10,500-plus species.
OK, I know this is a bit more mind-taxing than my usual meanderings, but hey, we all need challenges time to time.