The unripe fruits of mulberry trees are hallucinogenic,and birds eat the ripe ones. White mullberry trees are everbearing,are the ripe fruits are whitish and hard to tell apart from the not-quite-ripe ones. Eating hallucinogenic berries would seem to be bad for a flying animal,so either they can tell the ripe ones apart from the not-quite-ripe one by smell or they use vision and are very good at seeing subtleties in color. Maybe birds,passerines or whatever, are immune to these toxins.How do they manage this problem? Thank you.

I suspect that birds have evolved so the fruit (ripe or unripe) are not toxic or hallucinogenic  - for the reasons you outline above.