Back in the late 40's early 50's, my grandfather swears that a blue jay cost him a really nice buck in the Ithaca, NY area. To his dying day in 1969, he hated blue jays and kept a pellet rifle handy to "remove" them when he saw them.
If you learn to listen to and identify other animals calls, they will let you know when something is amiss-deer, fox, hawk, owl, person, etc.
A number of years ago, a guy kept a pack of beagles in a kennel on the property next to where I hunt. When his dogs got to carrying on, it usually meant that there were deer moving in my direction. Usually, when the dogs are restrained, deer move freely around them (they feel safe). The dogs will bark and carry on when they see or smell the deer. I have watched deer at my house graze/browse less than 100 feet from my dogs when I let them out in my fenced yard. The deer keep an eye on the dogs but they don't run off.