[yorkietalkjilly]

LOL. Not at nothing. There are many reasons dogs growl or bark after dark.

People and critters all grow tenser and more alert and watchful after dark out of instinct. In the wild, canines and humans must preserve self and pack after dark when mountain lions, coyotes, fox and other predators hunt.

Terriers were bred to catch vermin and other nocturnal critters and they must therefore be more alert after dark when those animals are active. They know when a critter is on your property or in your attic, house or walls. Also, our dogs sense our tenseness when we hear an unusual sound after dark -one not nearly so ominous when it happens during the day - and after this happens a couple of times, it becomes a pattern of tension the dog picks up on and learns. He responds and becomes tenser. He begins to subtly connect that this usually happens after darkness and soon, will just tense more as darkness falls just because he's learned to do that from you. All canines tend to be more unsure after dark, when shadows loom and their vision isn't quite as sure and they tend to go more on what they smell and movement that they can see. They have far more light receptor rods which pick up motion/movement and larger pupils that let in more light so they see better than we do but even their vision isn't quite as good after dark as daylight. So they are necessarily more alert when one of their senses is a bit diminished. And if the dog is suffering any loss of vision at all with age or illness, night will increase that problem. And you get a tenser dog - a dog ready to growl and alert.

So take their canine instincts to be alert after dark on top of the tension they sense from us at night, terrier heritage to hunt nocturnal critters, slightly diminished eyesight and you get protective and guarding type behavior.

During the day my Tibbe hardly ever has any reaction to subtle things going on outside - well, except the mailman, garbage trucks, squirrels and cats. But after dark, he will alert to people coming and going near our property, neighborhood cats out and about and even wind, house-creaking, etc. He's a far different dog after dark and it is that instinct that makes a good watchdog.