At my old house, there were all sorts of snakes including several species of rattlesnakes. We got peafowl because I really wanted them just cuz I admired them- did not know about them being snake killers/repellents at that time. Anyways when my pair became a flock of free range peafowl(never confined, not even for the nights), all of us noticed a major drop in seeing snakes inside our yard. The one neighbor who hated birds and encouraged his young sons to throw things at and chase them out of the yard continued to find snakes (including rattlers) warming themselves up on their front porch. We used to have the same experience(both of our porches were brick/cement and faced east) but not any more after the peafowl....
I got to witness a couple encounters though, what they did with large snakes: went up to them, their behavior attracted other peafowl, so there would eventually a group of several birds surrounding the snake and eventually one or more would get worked up and start biting the snake's tail to 'hurry it out of here'.. if the snake took on a defensive position they would either start biting it or one would give it a 'karate kick' and that was usually good enough to get them moving until they left the yard or were forced out of sight under a rock/structure. Rattlers got big reactions(usually several of the birds would honk or scream- don't recall them doing that with king or gopher snakes), I guess because of the way they raised their heads/necks up high/fast strikes plus of course the noise from their rattles. They would bother them until they moved out(some of the rattlers actually moved away fast without attempting defense)
Now with the permanently penned up peafowl at my current location, for some reason they react much less.. at most a few would be 'curious' but basically do nothing to a snake, even a small baby one 12 inches or less. Friend who lives in the desert(theirs also permanently in pens/aviaries) reports pretty much the same reaction- when a rattler got in one of their aviaries, only one bird tried to check it out, the rest either didn't see or didn't care very much.
Also if the goal is snake repellent, would suggest having a group instead of only one. It seemed more eyes were better at spotting a snake, plus they seemed to 'egg' each other to bother the snake. As for concerns of snake biting a bird, I'm sure it probably happens but never witnessed a snake making contact with any of the peafowl that harassed them.. not even the rattlers. I suppose they have some 'instincts' from their native lands which apparently are full of poisonous snakes- cobras, adders, vipers etc....
