The Food of the Gods (movie, 1976)

Morgan and his friends are on a hunting trip on a remote Canadian island when they are attacked by a swarm of giant wasps. Looking for help, Morgan stumbles across a barn inhabited by an enormous killer chicken. After doing some exploring, they discover the entire island is crawling with animals that have somehow grown to giant size. The most dangerous of all of these, however, are the rats, who are mobilizing to do battle with the human intruders.