Did they really shoot chickens in the opening shot?!!

Highly likely those were real chickens, laws on those things weren't as strict back then even in the US. I don't "like" these kind of things, certainly in this instance I think it was quite a pointless killing of animals. But in general I'm certainly not going to go all PETA on film crews for using live animals and maybe even killing them. But this scene was pretty pointless and unnecessary IMO.

I would rather watch an "historically accurate" depiction of life as it was then, than some made up fantasy of how you think it should of been! Look, those chickens got eaten.

I'm just going to answer your question. Most of the posts here are about whether or not it's wrong that they killed chickens.

The chickens were buried up to their necks as you see in the film. The weight of the dirt caused them to fall asleep.
To keep them active, and alert, gasoline was sprayed in their eyes.Squibs were affixed to their necks, and they were set off at the appropriate time.

Their heads were not shot off. They were blown off using a small explosive.

Years ago I saw Peckinpaw on a TV talk show and a man in the audience mentioned this in an irate way. He answered by saying they ate the chickens and they were good. That's pretty much all he said.

I prepare my chicken this way. When I saw the movie I said out loud "finally a proper chicken fixen!"

www.thecultofhorror.blogspot.com

The point is that: Neither of these two characters are likable. That they get off on shooting the heads off of chickens for sport proves this. They are both violent men with zero regard for human life. They shoot people in the back. Gives you an idea.

I get the "using the chickens for food afterwards" thing. But, it's highly unlikely that poor people would be spending precious money on guns and ammo when they could use an ax, a machete, or whatever.