It’s instructive to compare the feeding behavior of birds at our sunflower feeders. Some, like house finches, purple finches, northern cardinals and evening grosbeaks, will sit on the feeder and crack seed after seed with their powerful, crushing bills. Others, like black-capped chickadees, nuthatches and tufted titmice, swoop in to grab a seed and then fly away with it.

Birds in the latter group have relatively small bills and can’t easily crush a sunflower seed to get to the kernel inside. Instead, one of these birds will take the seed to a more protected area, holding the seed firmly beneath its feet as it perches and chisels the sunflower seed apart with well-placed strikes at the suture line.

This process takes time and focused vision, so a chickadee’s guard is down. Chiseling a seed open in full view at a feeder is risky. Finches can crush a seed easily without having to use their eyes to accomplish the task. These birds can keep a watch for predators without having to retreat to a protected area.

If you watch a chickadee after it flies away with a seed, you can often see the bird perch and hammer the seed open. Sometimes it will eat the kernel, but at other times it will cache the kernel behind a scale of conifer bark, in a crevice, or among needle clusters of evergreens.

Many species of birds from diverse families hoard food – usually seeds, although insects and other animal matter may also be cached. One could consider voles or birds impaled on a barb by northern shrikes to be a type of hoarded food.

Hoarding makes sense for resident birds because food supplies always vacillate. Birds that are nonmigratory have two choices: wander widely in search of patches of food, or store food when it is abundant to use in times of scarcity.

Hoarding has been well studied in black-capped chickadees. We’ll use this species as a case study in food hoarding.

Chickadees mostly cache food in the fall. October and November are the peak months; hoarding is only rarely seen after December. During peak hoarding, a black-capped chickadee can store hundreds and even thousands of food items in a day. A study of a related species in Norway indicated 50,000 to 80,000 seeds were stored each autumn.

Chickadees store each seed in a separate location. This dispersed storage is called scatter hoarding, as distinguished from larder formation, where the food is stored in one place.

One might surmise that hoarding is more important at higher latitudes, where the winter is more severe, and available information supports this. Hoarding by black-capped chickadees is common in Ontario and New York but has been documented only once in southern Illinois.

Scatter hoarding is advantageous because a competitor cannot possibly find all the cached food. However, hiding food demands a prodigious spatial memory. Chickadees are up to the task.

Work by David Sherry at the University of Toronto showed black-capped chickadees can accurately relocate caches 24 hours later. Subsequent work shows these spatial maps can persist for as long as 28 days.

Chickadees spent more time in the vicinity of their caches than in areas where they had not hoarded seeds. Furthermore, chickadees allocate most of their time near the caches where their most nutritious food has been hoarded.

Most food items are recovered one to four days after hoarding. So how can hoarding be of value in the dead of winter? The answer seems to be that chickadees remove cached items and hide them again in a new place for a few days, moving them again and again until they are finally eaten.

Herb Wilson teaches ornithology and other biology courses at Colby College. He welcomes reader comments and questions at:

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