Ridiculous pathetic Q: there's a bird dying outside my house, should I kill it?

[Myrddraal]

I just came home to find a Magpie killing chicks outside of my house. The magpie flew off leaving a very badly hurt chick lying on the floor, panting and calling. It's pretty nasty. I figured I should finish the thing off, put it out of it's misery, so I got a mallet thinking I'd whack it as hard as I could. When I get to it I'm having a hard time, even though it's going to die eventually, this chick isn't behaving like it wants to die now...

Also, I've never intentionally killed anything in cold blood bigger than a fly, and I must admit it's making me uneasy.

Is this the worst form of cowardice on my part, or am I being reasonable in letting this thing live a few more minutes?

EDIT:
Ugh. The thing is still breathing. I never thought I'd be so affected by something so pathetic. I've watched birds of prey hunting and never thought more than "wow!" but this chick is so pathetic and vulnerable, and quite clearly suffering.... gah!

EDIT 2:
The question is, will it suffer more if I leave it to die in pain, but without me looming over it wielding a mallet? Would it really be a mercy to kill it? Am I only asking myself these questions because I don't have the guts to whack it?

EDIT 3:
There's a pigeon unconcernedly picking at the grass next to this poor thing. I mean literally, picking cm away from it, almost standing on top of it. I almost wish I could be as cool as that pigeon.

EDIT 4:
A blackbird (male I think, it's got a tinge of brown but quite dark) has just turned up and is showing more interest in the chick. I think I'll leave them be.

EDIT 5:
The blackbird has gone, but the chick is still alive. It hasn't moved from where it was lying.