Filling the Larder for the Winter

I always am interested in noting the behavior of the birds I am watching.  The birds in my local patch have telling me a lot lately by their actions.  In particular, the feeding behavior of the birds has really caught my attention over the last couple of weeks.  The Neotropical migrant warblers passing through my patch on their way south to their respective wintering grounds have been feeding voraciously on any insects, spiders, and other arthropods they can find.  It’s a nonstop flurry of activity for these birds as they pack on the calories for the immediate task of accomplishing long-distance migration.  The resident birds – Black-capped Chickadees, Tufted Titmice, and White- and Red-breasted Nuthatches – are showing a very different behavior right now when it comes to food. 

          Instead of gorging themselves in preparation for a long migration journey, they are making seemingly nonstop forays to and from the seed feeders.  They are not eating these seeds, but rather are taking them away and storing them in crevices, under bark, and in lots of hiding places.  Later, during winter, they will re-find these seeds and eat them as a source of protein and fat to get through the food-scarce months of winter.  This act of filling the larder for the winter is called food caching.

Black-capped Chickadees at my feeder selecting sunflower

seeds to cache out in their winter territories.  Photo credit: Jody Enck

          Among the birds North American birds that are known to cache food are various species of Corvids (i.e., Jays, Crows, Nutcrackers), Parids (i.e, Chickadees, Titmice, Nuthatches), and some Woodpeckers (e.g., Acorn is the most well-known, but some Hairy and Downy Woodpeckers also cache).  These birds will go back and re-find their caches months after they are stored.  A few other North American bird species store prey items for the short-term.  These include some American Kestrels, a few of the smaller owl species (e.g., Boreal and Saw-whet), and of course, Shrikes.

          Evolutionarily, caching of food seems to have emerged from those groups of animals that take food to their young (as opposed to taking their young to food as in precocial species like turkeys, grouse, ducks, and shorebirds).  This occurs in some species birds, some mammals (e.g., Chipmunks), and some wasps (yes, wasps).  But, food caching is performed by only a small minority of species in those groups. 

A Black-capped Chickadee flies away from my feeder

with a Sunflower seed to cache somewhere in the woods. 

Photo credit: Jody Enck.

          Various species of Jay are particularly adept at caching food, and take their behavior even farther than the Chickadees, Titmice, and Nuthatches.  Jays are particularly good at being thieves.  That is, they watch other birds caching food, and then steal those food items and re-hide them for themselves.  Apparently, Jays that are thieves themselves, have learned to be extra careful when they cache their own seeds.  These birds watch the other birds around them.  If they notice that they are being watched by other birds that might subsequently steal those seeds, then the Jays go back after the other birds are no longer watching, and they re-hide their own seeds so they don’t get stolen by the other birds.

How do these birds remember where they cached the seeds so they can retrieve them later?  Some studies have found evidence that the environmentally stressful conditions faced by food-caching birds (think cold, snowy winters that make finding food difficult) cause slightly elevated levels of glucocorticoids (especially corticosterone) in their brains.  The elevated levels of these steroids, which are naturally produced in the adrenal gland, improve the spatial memory of these birds.  Release of corticosterone actually increases the size of the hippocampus part of the brain – that part of the brain that involves spatial memory.  This makes the birds better able to recall where they cached these seeds, makes them more efficient at finding food during the environmentally stressful winter, and increases their chances of surviving.

A Tufted Titmouse repositioning a sunflower seed

in its mouth by holding it briefly in its feet.  This bird

flew about 150m away into the woods to cache its prize.

Photo credit: Jody Enck.

In my patch, I love watching the birds making forays to the feeder, grabbing a sunflower seed, and flying off into the woods to hide their prize.  I conduct a point count in my woods about 150m from my backyard.  This time of year, it is fairly common for me to sit at my point count and watch Nuthatches, Titmice, and Chickadees bringing sunflower seeds out into the middle of the woods and hiding them in various crevices under the bark of trees.  Later in the winter months, I’ll enjoy sitting at my count site and watching these birds re-find and eat their cached food items.  When the birds fill their larder with these seeds, it not only ensures that they will have food to make it through the winter, but this food-caching behavior ensures that I'll have more fun behaviors to watch as these birds re-find their prizes when the snow flies here in my part of the world.