This is the process of bio-accumulation. A grasshopper may eat a nonlethal dose of a pesticide and then get eaten by a shrew. Because the chemical does not decompose it is stored in the shrew's body. Every contaminated grasshopper that the shrew eats adds more pollution to its body. It is unknown the effects this pollution will have on the shrew but sterility, birth defects, or shortened life span are likely outcomes.
Hawks eat several shrews.
Therefore, the chemicals accumulate greatly in their body tissue. This has been known to cause the thinning of egg shells and thus reduced ability to reproduce. Some birds may also be born with crossed bills which drastically reduces their ability to feed and death is a likely result. Some convenient way of telling the shrews and the hawks from grass- hoppers. They could wear capes, hats, signs hung around their necks, etc.