Monarch on Joe-Pye Weed

I took a stroll into Petro Canada Park this morning and found a couple of monarch butterflies feasting on the flowering swamp milkweed. They were so busy sipping their breakfast that they paid no attention  to me as I moved my macro lens closer and closer. Can anyone tell me if it's a male or a female? Apparently they have slightly different markings.

3D cross-view of Monarch butterfly