Weasels do kill some gamebird chicks, but probably very few. Weasels have no legal protection in Britain. In bad rodent years many weasels starve and few of the survivors breed. Local populations often experience extinctions. However, weasels are extremely good at recolonising abandoned areas when conditions improve.
Stoats are larger and have longer tails which end in a black tip.
Stoats may go white in winter, but weasels in Britain do not. I have seen a weasel running round and round in a circle, leaping about and somersaulting. This behaviour could be a response to extreme discomfort caused by a large parasitic worm commonly found in the nasal sinuses of stoats and weasels. The presence of these worms causes distortion of the skull bones and consequent pressure on the brain. This, along with the wriggling of the worms must result in extreme irritation, and may affect the weasel's behaviour.