Was the behavior out of the norm for ravens in a significant way? It sounds like they may be searching for food, did not find something in your front yard, and departed. Perhaps it didn't seem safe enough after they landed.
ravens are ravens indeed but sometimes they are strange...
For example, once I was riding my bicycle and on my way was a raven next to the road. Normally all birds fly away when someone passes by with a bicycle.
This raven decided to do a suicide attempt by walking from the side towards my front wheel...at that point I was exactly cycling over the raven and I heard like something crack...Afterwarrds the raven flew away.