Magazine article Natural History

How to Eat Sunflower Seeds

Magazine article Natural History

How to Eat Sunflower Seeds

Article excerpt

Hummingbirds suck flower nectar through straw-like bills; red crossbills pry apart tightly-closed spruce cone scales with their crossed billtips; heron spear fish; hawks tear flesh; chickadees pick tiny insects off twigs; tree creepers use their bills as forceps to reach under bark; and woodpeckers drill into wood. Despite the legendary diversity of birds' beaks, I had taken for granted how birds eat sunflower seeds. The process is not something I would think to watch or think about. Throughout North America, people feed birds countless tons of sunflower seeds. According to the U. S. Department of Agriculture, "cultivated sunflowers are one of the five largest oilseed crops in the world." And a quarter of the crop goes into birdseed. At the feeders next to our cabin in the Maine woods, twenty-three species of birds-by my last count-consume 400-500 pounds of sunflower seeds every winter.

To eat a sunflower seed from a feeder should be simple for any bird. But sunflowers don't grow in the Maine woods. So, to these twentythree species of birds, this food is exotic. Birds first need to discover there is a nut inside the shell. About twenty winters ago, before I started buying black oil sunflower seeds-with their thinner shells and higher fat content-I bought striped sunflower seeds to feed black-capped chickadees and red-breasted nuthatches. I noticed these birds were picky eaters; sometimes they came to the feeder, picked up a seed, and flew off with it, but often they picked up a seed and flung it aside. One winter, when I was teaching an ecology course, I pointed out this behavior to three of my students and asked them why they thought the birds did this. No one had any idea. So, we made some observations and did some experiments. Our results-long since published in The Auk, an ornithological research journal-showed that the birds discriminated by weight; they dropped the light ones and flew off with the heavier ones. The light seeds contained no nut. This exercise, however, did not explain how these two species of the deep woods had come to know sunflower seeds. An informal and unplanned experiment gave a clue.

As I recounted in "Chickadees in Winter" [3/15], when I first put up a well-stocked bird-feeder next to my cabin, no takers showed up for a month. Perhaps, the birds were reluctant to come to our clearing, so I hung it up in the nearby woods. A week or two later, it was being visited by chickadees, not just one but several at once. I took the feeder off the tree and slowly carried it toward the cabin, stopping every ten meters, or so, to hang it up before continuing. Within an hour, it was next to the cabin where it had been before, but this time it attracted a crowd. Within weeks, various species of birds appeared. Birds follow each other to food that has been discovered. Now, when the feeder is hung up in the fall, chickadees are there within a day.

Getting the nut from inside the shell of a sunflower seed is no problem for squirrels, the birds' main competitors for seeds. Squirrels rotate a seed in their paws and cut off bits of shell with their sharp incisors. But birds have neither paws nor teeth, having lost the latter as they evolved.

I first started watching chickadees at our feeder to observe their seed caching behavior. But not once in all these years have I seen a chickadee cache a black oil seed. Instead, they eat them as quickly as they can, given some constraints. I've timed several. It takes them thirty-fifty-five seconds to process one seed. Chickadees grab a seed with their bill, fly to a nearby maple tree and perch on a branch that is slender enough for them to put both their toes around it and over the seed. With the seed securely held to the branch, they begin hammering it with their bill. As soon as they extract a kernel and eat it, they fly back to the feeder and repeat the process, over and over. Blue jays use the same technique, except they chose a larger branch to hold the tiny seed more securely with their much larger feet. …

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