Smart Birdbrains

Things got a bit exciting around our house the other evening. The big cat came in through his little cat door carrying a grouse. A live, healthy, adult grouse. After a brief period of tumult and some bad language in the voices of three species, the bird left through the human-sized door. It was short of feathers and dignity but otherwise seemed well.

I had considerable time to muse upon the situation while I cleaned up scattered feathers. The cat and I have an uneasy truce about his hunting. I don't much care for it. Yet I understand that he is trying to contribute his fair share to family support when he brings critters home; we open cans for him, he brings home fresh meat for us, undismayed by our refusal to eat it. His skill has other values as well. There are no rabbits in the family cabbage patch, no squirrels in our insulation, no voles in the pantry. They keep their distance, or become cat food.

Despite his skills, he seldom catches some animals of catchable size. That gray jays evade him I can understand; they're smart and wary. But he doesn't catch chickadees, and that seems peculiar. The little black-capped twits abound in his territory, and they don't seem as smart as jays.

Thoughts of cats and birds were still on my mind when I came across an article in the September issue of Discover magazine that may have a bearing on why black-capped chickadees rarely fall to the cat. The article dealt with bird brains.

University of Toronto psychologist David Sherry suspected that birds wintering over in northern climates necessarily had some mental skills superior to those of birds that migrate south. Though a theory of this sort automatically appeals to north-country chauvinists, his idea rose from observed behavioral differences rather than pride in Toronto's latitude.

Many northern-resident birds store food for the lean times. Especially in the fall, they stash edibles in safe places, building as many as 200 caches in bark crevices, hollow stems, or under leaves. Those caches would not keep the birds alive unless they could remember where the food was hidden. They need good memories.

To test whether memory does play as large a role as he suspected, Sherry and colleagues provided a flock of nine black-capped chickadees with an artificial forest--a 10 by 12 foot aviary supplied with plenty of good hiding places for seed caches. The researchers took careful note of where the birds located all their caches, then removed the birds. With the birds safely out of sight, scent, and sound of the aviary, the researchers picked up all the cached food.

Twenty-eight days later, the scientists returned the flock to the aviary. The birds immediately flew to their cache sites, even though the stashes were now empty. Clearly the chickadees weren't following any physical clues to the food location---there was no food left for them to smell or see. They were operating on memory; they remembered where they'd put the spare food.

When Sherry's group autopsied dead birds, they found further support for the view that food-storing bird species have better memories than bird species that don't make caches. It's long been known that in mammals a brain structure called the hippocampus is important for memory, so they compared the size of the hippocampi in 23 different kinds of birds. Bird species that store food proved to have a much larger hippocampus than birds that don't---in some cases, twice as large.

Memory is only one kind of brain power. That chickadees have both the brain structure and demonstrated capacity for remembering doesn't mean they have notable intellects in other ways. But---speculating freely here---it's easy to see where a good memory could be helpful in avoiding a resident predator. If a chickadee can remember something like "seeds stored under loose bark, fifth branch up on the left," it can probably remember "dangerous striped animal lives near here--keep watch."

I'll settle for that solution. I just wish grouse had better memories.