Chest bumping

[Amanda0419]

I am a new chicken owner!!! I have 8 chicks that are 2.5 weeks old. Today I noticed a barred rock picking on a speckled sussex when I let them out of their brooder for a little field trip. Is it normal for chicks at this age to chest bump and stare each other down? The BR was the one initiating everything and the SS just stood there. Looking at the markings on the BR I believe she is a pullet. I'm not sure about the SS though. Is this a normal behavior for pullets or does it sound like this may be a male thing?

These are the birds in question

 

[chickens really]

Those are normal little mock battles between Chicks..It's play and pecking order..How they learn to become one flock..