Apparently this is a proverb that means "It will be obvious" or "You will know it when it happens." Alternate translation: "It will be as obvious as it is when vultures gather around a dead body" or "As the gathering of vultures shows that there is a dead body, there will be signs about these things"
Vultures are large birds that eat the bodies of dead animals that they find. You could describe these birds this way or use the word for local birds that do this.