Aggressive chick?

[ohnoicantfly]

I have three 1.5 week old chicks that I've been raising. They are all co-exist well with each other, but whenever anyone puts their hand in the brooder, one of the chicks will jump and flap at their hand and sometimes peck if you try to pick him up. Is this chick a rooster? Or is this chick just aggressive? He almost seems to be defending the other chicks.

 

[Ferd Berfel]

We had one that was slightly larger than the others. It always jumped between your hand and the smaller ones. It turned out to be a very sweet hen, probably 4 years old now. One of very few that has a name, Amy. I don't know why she is named that.