They both can be found in the same food chain, but they aren't directly related. A hawk is a tertiary consumer (top of the food chain) and grass is a producer (bottom of the food chain). The hawks survival depends on grass:
Grass feeds on nutrients from the ground → insects eat grass and flowes → bigger insects eat the smaller insects → field rats eat the insects → hawks eat the field rats.
Hope it helped,
BioTeacher101
