Our Rottie mix is wonderful with our chickens. She was slightly annoyed when my daughter's ducklings followed her around for 30 minutes when we first got them, but just looked at me to rescue her. I have no idea of her background before 18 months since she was a rescue, but we couldn't ask for a better dog. She has only chased our birds once, and that was when the Rooster and the duck were fighting- early in our chicken experience. I thought she was going after them, but it turned out she was just breaking up the fight like she does with our kids. LOL. (Rooster and duck get a long now... too well, but that's another story.) She came immediately when I called her off. While I don't leave her purposely unsupervised with chicks, she's around them a lot and will smell them and then walk away or "guard" them in the yard as they walk around when I'm outside.
Our Schipperke (~15 lbs) will chase the hens (never the Rooster or duck) on occasion, but she's cornered them before and then she runs away, but usually they just fly if they see her coming in a chasing mood. It seems they can tell. She's just ornery and likes to frustrate me. She NEVER does it unless she knows I'm watching. Brat.
Our wimpy, old, mini daschund (~6 lbs), on the other hand ate a chick once. Walked up to it calm as can be and swallowed it whole. The kids were cleaning out the brooder in the utility room and left the door cracked. After we all got over the shock and horror it was actually somewhat amusing. We never gave her the chance again and she passed away earlier this year.