AP PSYCHOLOGY

Maria wants to know if birds prefer to eat in one place over another. She makes three feeders out of 2-liter bottles and paints all of them red. She fills each of the feeders with the same amount of mixed birdseed, and plans to keep the feeders out for 10 days before measuring how much seed is eaten from each feeder. She puts each of the feeders in her back yard:one feeder in a large dead tree, another feeder she sits on the dog house, and the last she sits in a small bushy tree.What is the independent variable?