Is this a male trait? I have a 12 year old female sheltie. I've owned her for 3 years. My folks owned a female from about 2 years till she passed on at nearly 20 y/o. My sister owns a female which they bought as a pup and she is nearly 4. I don't remember this trait in either of my family's dogs and of course didn't have my lovely lady when she was that young. I would love to have another sheltie some day and am wondering if this aggression is a trait of a male or if it has been seen in females of the breed as well.