2. (a) That's right. But did you apply the appropriate principle correctly?

You ought to have applied the principle 'ex abundanti cautela' to the phrase 'chickens, ducks and domestic poultry'.

The mention of two specific animals followed by a broad category of animals suggests that the chickens and ducks are mentioned to ensure clarity, rather than to narrow the meaning of the whole phrase. The result is that the phrase should be interpreted to include all domestic poultry.

You should have realised that the principle 'expressio unius' cannot properly be applied to this phrase.