Paint the wood with chilli extract and mix ground dried chillies with the bird seed. Bird's don't have the receptors to be affected by the capsaicin but squirrels do and they don't like it.
Although, there's always the danger that you may breed a strain of hard-core chilli-head squirrels.
Although, there's always the danger that you may breed a strain of hard-core chilli-head squirrels.