buff orpington - hen or rooster

[dinmonroe]

We purchased six "hens" from a reputable feed store that's been in business for decades. We are now wondering if one of our hens is actually a rooster. They were babies in March. How do we tell?

 

[Celtic Hill]

Their comb size is the best way to tell, also my BO rooster is larger then my hen, and they were hatch mates.