Washing the dishes after a family dinner is a big job, especially because my mom’s kitchen doesn’t have a dishwasher. But the window over the kitchen sink looks out on several bird feeders, and my dad makes sure they are always full of seed and ready to entertain.
Black-capped chickadees are the most fun. They dart in, grab a single seed, and swoop off to eat it in a spot that’s less exposed than the feeder on a second-floor deck railing. This is similar to the feeding strategy of a ruffed grouse, but on a much smaller scale. As I wrote last week, grouse will stuff their crop full of buds and catkins for about twenty minutes, and then fly off to a protected place to digest all night. Grouse increase the size of their gut to accommodate this practice, but chickadees have kept their stomachs small and increased their brain size instead.
Chickadees gain up to ten percent of their body weight in fat each day, and burn it off each night to stay warm. Even though they wedge themselves into a tiny tree cavity, puff up their feathers, and drop their body temperature by 18 degrees, they still need to shiver all night to generate heat. They don’t have energy to waste by maintaining both a large digestive system and a large brain. Getting too bulky would leave chickadees less agile and more vulnerable to predation, anyway.
One way that they find a balance is by hiding seeds—essentially storing fat outside of their body. Often, when a chickadee nabs a seed from your feeder, they don’t eat it; they stash it away for later in the bark of a tree or under a leafy lichen. This allows them to dole out their calories more efficiently and prepare for a “rainy day.” Eating just a few nutrient-rich seeds at a time also means that their stomach can stay small.
Chickadees cache as many as one hundred thousand food items per year. Unlike squirrels, chickadees don’t go sniffing out their hidden seeds. In lab experiments, scientists have determined that chickadees use visual cues—especially big ones like the location of nearby trees—to re-locate their cache sites. Not only do chickadees remember their seed cache sites, but they also remember details like which food items were the most favored and which seeds have already been eaten by them or by a thief.
To support such an incredible memory, chickadees grow 30 percent more neurons in the fall when caching behavior peaks. Then, as they empty out their cache locations, the neurons encoding that information wither away, and their brain shrinks toward spring. The title of a 2014 article by Kozlovsky, et. al. says it all: “Chickadees with bigger brains have smaller digestive tracts.” Chickadees, especially ones who live in the coldest and most variable habitats, have figured out how to eat smarter, not bigger. That could easily be my New Year’s resolution.
Last April, researchers at Columbia University added to our understanding of chickadee memory. Selmaan Chettih, and Emily Mackevicius, with the help of principal investigator Dmitriy Aronov, placed chickadees in what they call an arena—which sounds to me like an avian version of the Hunger Games! The arenas were built to look like a chickadee’s usual habitat, with plenty of nooks and crannies for hiding seeds.
As the chickadees conducted their typical caching behavior, the scientists recorded their movements with cameras, while also monitoring activity in their brains. Each time a chickadee hid a seed, their neurons fired in a unique pattern. When the chickadee retrieved that same seed, the pattern was repeated. Each cache got its own pattern. The scientists dubbed these “neural barcodes.” The birds are essentially creating their own system for inventory and checkout—just like at a grocery store!
Even though chickadees and grouse have evolved strategies that are on opposite ends of the brain-stomach spectrum, they are both good at surviving when we leave their habitat and natural food sources intact. Even when chickadees have easy access to your feeder, only about 21 percent of their daily energy comes from your generosity. The rest they gather from the wild.
As a result, the scientific consensus is that birds don’t become dependent on feeders like the ones in view of my mom’s kitchen sink, and will find other food sources if you go on vacation. That said, your gifts are appreciated. Years ago, Margaret Brittingham and Stanely Temple at the University of Wisconsin—Madison, observed that when cold temperatures lasted for more than five days, chickadees with access to bird feeders had higher survival rates.
Since I love watching chickadees while I wash dishes, I’m quite happy to continue feeding their big, black-capped brains.
Emily’s award-winning second book, Natural Connections: Dreaming of an Elfin Skimmer, is available to purchase at www.cablemuseum.org/books and at your local independent bookstore, too.
For more than 50 years, the Cable Natural History Museum has served to connect you to the Northwoods. The Museum is open with our brand-new exhibit: “Anaamaagon: Under the Snow.” Our Winter Calendar is open for registration! Follow us on Facebook, Instagram, YouTube, and cablemuseum.org to see what we are up to.
Last Update: Jan 02, 2025 7:35 am CST
