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.
shira2

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.”

Dispersal

Gliders, dogs, tennis balls, crossbows, inviting packages, blowguns: just a few of the mechanisms devised by the M Groupers to meet the annual Seed Dispersal Challenge.  After the class studies different means of dispersing seeds through wind, water, animals, and propulsion, students create their own way of getting a bean seed to travel at least 3 meters away from themselves.  Use of their own muscles is restricted to one small movement of the fingers – as in, drop a seed or glider, or release a trigger. The seed has to land on a surface where it could potentially grow, and a logical argument must be made for how the next and future generations could use the same technique to disperse their seeds as well.  Attaching a seed to a ball and letting gravity roll it down a hill, for example, only works for one generation, as the next will not have the same gravitational benefit. maggieOver the years, I have witnessed countless ingenious solutions, including loosely taping the seed to the top of a 3-meter long pole, then letting it topple over to release the seed.  This seed would then ostensibly grow into another tall pole-plant, which would disperse its seed in the same way. Or there was the seed attached to a soccer ball, which was left on the grass and eventually kicked away by a passing child who was unaware of the challenge, but who couldn’t pass up the obvious invitation.

During aftercare today, I noticed a dozen or so familiar-looking saplings growing under the canopy of the pines: golden rain tree.  A large, non-native ornamental now considered invasive, a single tree had been planted about fifteen years ago, succumbing to an unknown disease just last summer.  In those fifteen years, it had produced prolific pods bearing wind-borne seeds, but until now I had never seen its offspring.  So many inadvertent plantings, and these were only the visible ones. The saplings were just beginning to reach above a thick growth of other introduced, invasive plants: garlic mustard, wine berry, and burdock. Osage orange and yellow buckeyes, prized in the Jemicy fort culture, are not native to this region either. They join the golden rain tree and other introduced plants in that enormous pantheon of species that humans decided, for one reasonparkerseeds or other, to bring here.  And once established, facing no native controls, most take over dispersal responsibilities with the utmost success.

“Are all introduced species bad?” “Are all native species good?” “But don’t we want more species for biodiversity?” These are questions from students that I can’t definitively answer. What I can say is, “Look around you. Which kinds of plants are there the most of? Which kinds are there very few of? Does it seem like some are growing “out of control”? And then we look for the stories of how certain species got here – why humans decided they wanted them, and the effect that they have on others. I hope from this they will take away at least one message: dispersal doesn’t end with the single seed that we successfully launch; it is just the beginning.