The Sky Raptors fed off other creatures. They hunted the Nu-Humans who settled on the planet. They hunted on creatures which were alive, but also fed off the dead bodies of Nu-Humans.
Some of them also tried to hunt the Eleventh Doctor, Amy Pond and Rory Williams, during their visit to Hope Eternal. However, the Doctor and his friends were saved by Trevor Reardon. (AUDIO: The Nu-Humans)