The ecosystem of an experiment

Do birds prefer popcorn or sunflower seeds?

M Group is in the middle of conducting their annual seed preference experiment. They each make a simple bird feeder from a plastic container, count out equal numbers of popcorn kernels and sunflower seeds, and hang it with a suction cup from a window at school. Every day for ten days, they check their feeder to count the remaining seeds, record and replace the seeds taken.

This experiment on preferences had its genesis in a grad school ecology class.  We were required to devise some kind of quantitative study where we could practice field work and data collection.  While my classmates studied coyote foraging, tree cover, and dragonfly mortality, I decided to embed the study in my class focus on oaks – specifically, whether certain weights of acorns are preferred by gray squirrels.  We designed and built squirrel feeders and filled them with a 50/50 mix of red oak acorns that had been cadata1refully weighed and sorted into “heavy” and “light” categories. As with the bird feeders, they did daily counts of remaining acorns and replaced those that had been taken.  The statistical analysis of our data showed a small but significant preference for heavier acorns.

But these results were insignificant in and of themselves.  They were simply one by-product of a vast array of interwoven learning experiences engendered by the experiment.  Just by following required procedures, the fourth graders learned how to set up a scientifically sound experiment, the importance of controlling variables, how to measure, to record data, and how to make sense of a set of numbers.  But beyond this, the experiment expanded in ways I could not have foretold.  The kids began to ask questions like, “Well, if squirrels take and bury more of the heavier acorns, won’t more of those grow into trees?  So won’t oak trees make heavier acorns over time?” This intuitive grasp of natural selection stunned me.  I also saw kids starting to spend their recess time “staking out” their feeders, in an effort to determine whether other animals such as blue jays and chipmunks were visiting them.  More than once, a child reported that, not only had no acorns been taken, but there were MORE acorns in the feeder than had originally been put there!  What was up with that?  The interest in animal behavior sparked by this experiment continued well beyond the fall and into the winter, when the kids saw that I had hung bird feeders and wanted to know – of course – what kind of seeds the birds preferred.  And could they design their own bird feeders…?

The acorn experiment has since been shelved, but the experimental bird feeders remain a popular, easily maintained, and adaptable project.  Invariably, when the students are presented with the question of seed preference and are asked to make a hypothesis, most predict that more popcorn seeds will be taken. After all, the kids rationalize, each seed is slightly heavier than a sunflower seed, it takes more work to shell a sunflower seed that to swallow a popcorn kernel, you often see flocks of birds like crows and geese in corn fields, and more people eat popcorn as a snack (albeit not in kernel form).

It is precisely these kinds of inferences that science loves to challenge, test, and revise.  The more qualitative test that I relish is whether I will observe another transformation accompanying the empirical challenge.

birdbookOne fourth grader has been bringing a field guide to the woods during recess.  He sits by the stream near his fort and studies it, then accompanies me up the hill when the lunch bell rings, asking me questions like, “Is a purple finch the same as a house finch? Do we have them here? Why don’t they show a house finch if they live here?”  He asked his parents for a bird guide of his own. Because, he explained, “I’m fixing up an old feeder that a teacher gave me, and I want to see what kinds of birds come.  Maybe they will be different than the ones we get at school.”

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