Should this concern me?
 

I'm working a little earlier than normal this week, so I've been taking the dog out for walks at 4:30am.

THis morning she growled twice at people who were pretty far away - probably 100 feet of so, off to the sides (like coming out of their apartments or something). She NEVER growls at people - she loves people. I'm wondering if it was the strange hour or the day or she couldn't see them very well or something. It was really strange. Should I be concerned about this?

Trigger growled at our neighbor one time when it was dark-but he approached us, I'm thinking he couldn't see him well, because he didn't growl at him in the daytime.

is it still dark? could be she is having trouble seeing them

You know Sasha acts a little more on guard outside when its dark. That could be all it is. Keep an eye on this behavior and see how she reacts during the day vs dark.

So this raises a question. How good should these dog's night vision be? Jake's is great, but I wonder because with my collies PRA (Pogressive Retinal Atrophy) is a really big thing and all breeding stock is eye checked and rated. As Conner got older (he was a mild ) he had more and more trouble seeing in the dark. We knew that his eyesight was failing from that point.

Are eyes one of the weak links that should be part of health testing with these dogs?

we just went on a 3-hour walk and she was perfectly social to everyone.

I've noticed before that her dog aggression is much worse at night too. Maybe she doesn't have good night vision.

I don't think it has anything to do with there night vision. Night time is different, dogs can sense that and at night, things may not be as safe.

Has she ever reacted this way to people at night, as opposed to in the morning?

meh.... probably just insecurity due new walking time and things look different in the dark/dawn/dusk

no, she hasn't done it at night.