Orion has barked at noises she couldn't see since she was about 3 1/2 months old. She likes to hear herself talk.
I've seen her bark down a hallway, cock her head and listen to the echo..
I'm thinking she'll be somewhat territorial when she's older. When at my place in the city, she only barks when somebody knocks or comes into the house. My OH snuck in two days ago while Orion was sleeping with me thinking not to wake me up...
She leaped out of bed barrelled up the hallway and GROWLED. Then she barked her 'INTRUDER!!!' bark. When he came through the second door, she stopped dead, glared at him and barked loudly in his face and stomped off to pout with a very grumpy 'how DARE you!' look on her face. She wouldn't speak to him all morning.