Like was said - Hawks & owls are the biggest problem in most areas since the bannning of DDT.

Coyotes might eat quail - but most of the year they are on other foods and not targeting birds. How big a problem can bobcats be really? Probably House cats are a bigger concern.

Good luck with the program - I'd probably work on planting excellent quail cover crops like native grasses and sorghum. Also encouraging hedgerow growth.

FH