Respuesta :
In my opinion, you are trying to test if different type of food will affect different birds with distinct beaks. You are trying to see at what type of environment would one best be suited. Hope this answers the question. Have a nice day. Feel free to ask more questions.
What is the effect of . . . changes in the birds' environment (removing fruit) on . . . three separate bird flocks, each having their own distinct beak shape.