Turner often saw woodpeckers perched in trees in his backyard, but he never saw
them at his bird feeders. Turner usually
filled his feeders with sunflower seeds. He
wondered if he could attract woodpeckers
by adding a different type of food to the
feeders.
To test this idea, Turner gathered eight
identical bird feeders. He filled four with
sunflower seeds. He filled the remaining
four feeders with crushed peanuts. Turner
then placed the bird feeders in his
backyard. Over the next five days, he
counted the number of woodpeckers that
visited each bird feeder each morning.
a woodpecker at a bird feeder
Which of the following was an independent variable in this experiment?
the type of food used in the bird feeders
the number of woodpeckers that visited the bird
feeders