most years, severe cold temperatures destroy large numbers of grasshopper eggs. one particular year, however, a mild winter allowed the grasshopper population to increase. as a result, the frog and toad populations were well fed. insectivorous snakes and birds had plenty to eat also.
unfortunately, the grasshoppers were destroying the farmers' crops. to bring the grasshoppers under control, the farmers dusted their crops with a strong insecticide, killing the grasshoppers by the thousands. within a couple of days, however, various insectivorous snakes were found dead around the fields that had been treated with the insecticide. birds, however, that had consumed the same insects that the snakes had consumed were unaffected.

the birds might have survived because of

the nitrogen cycle.
biological magnification.
their range of tolerance.
the greenhouse effect.