Based on the hypothesis that ddt was causing a decline in fish-eating bird populations in the united states, a group of scientists predicted that the amount of ddt in bird eggs was correlated with the thickness of the egg shells. for their experiment, they planned to visit a number of fish-eating bird populations and take 1 egg from 70 nests. in the laboratory, they would open the eggs to measure the concentration of chemicals such as ddt. they would also measure the thickness of the egg shells. the researchers had to decide which species of birds they would use in their study. choosing the proper study organisms is very important because the species must be appropriate for the experiment, and practical to work with.