Caching Up for the Winter

It was one of those crip, golden days that couldn't decide if it was summer or autumn. The sun lit the treetops along the late-afternoon street. Most leaves were still green, but the maple at the corner was showing off its bright yellows and reds. A tall, brilliant yellow-orange goldenrod at the corner of our porch buzzed with the last furry bumblebees of summer.

Overhead, Turkey Vultures soared past, their silvery underwings glinting as they headed for their favorite roost in the trees along Cobbessee Stream, down below our house. A Northern Cardinal gave its "chip" call from the tangle of forsythia in the backyard. A crow called and appeared briefly overhead against the blue sky.

Then we noticed a Black-capped Chickadee hopping silently around the lilac before skipping over to the crabapple. Through our binoculars we could see that it was probing in the nooks and crannies of the bark. We assumed it was on the hunt for insects.

That's when we noticed the chickadee had a small sunflower seed in its bill. When it found the right spot, it tucked the seed into it and flew to the feeder in our neighbor's yard, just over our fence.

Moments later it appeared again, calling "chick-a-dee" from the weather vane on top of our garage. This time it tucked the seed it had brought into a space in the metal of the weather vane. (We'd seen birds cache in trees, but in a object made a metal? This was a first!)

The number of bird species that store or cache food for later use, as this chickadee was doing, is quite limited. And the behavior is only useful in species in which the individuals are planning on staying long enough to make use of the stored food later in the year when food supplies may be low. That rules out the usefulness of the practice for most birds that make regular annual migrations. In fact, theirtactic for dealing with food scarcity is to avoid the low-supply period all together by migrating to somewhere where there will likely be food available during the season when it's not available at the other place.

Another pre-requisite for birds evolving caching behavior is that they eat a type of food that won't spoil, and/or that they cache it in an environment that is relatively dry or cold. Canada Jays store scraps of fat and meat during the cold winters. Red-bellied Woodpeckers store acorns in holes they make in trees, which presumably make handy storage facilities that are dry enough to prevent the acorns from rotting.

What's amazing is that these birds actually remember the thousands of places where they have hidden away their food stashes. Studies have shown that in at least one species, the part of the brain that deals with remembering these details is larger in size as one goes farther north. This is thought to be because the birds farther north have more likelihood of starving during the cold and lean times of late winter so they need to store more food and remember all the places they did so, if they are to survive.

There are so many questions that spring to mind. Do birds that cache have a goal of a certain number of caches per day or do they only cache when there is a daily surplus? Are there some individuals that don't do much caching but sneak around and steal the caches of others? Is caching behavior something that is learned or do birds just do it inherently? Is caching behavior triggered each fall by temperature, seasonal changes, or something else?

That's the beauty of science. The more you know, the more you realize you don't know!

-Jeff and Allison Wells