I had this problem last autumn and the birds (Carrion Crows and Magpies) absolutely ripped my front lawn to shreds. Unbelievable, never seen anything like it before. I used Nemasys and it seemed to work unless the birds had got them all. Lawn still not fully recovered despite reseeding patches.
I'd have thought they would be OK in a cupboard if it was cool and not near a heat source. You can never be sure even if you followed the instructions exactly.