Nicotine is a poison that is odorless, and tasteless. The average cigarette contains 12+ mg of nicotine. Buy a pack of non-menthol cigarettes and dump the tobacco into a small pot of water. About 50 to 60mg is fatal to a full sized human so this should be more than enough to kill a bird. Let it stand there for a few hours. Because nicotine is a polar substance, it will bond to the water molecules. Strain the water through a coffee filter, and throw away the tobacco. Nicotine boils at 123-125° C, so you can boil the water until you have a reasonable amount of the substance. Add bird seeds and continue boiling for a few minutes. Put that shit out side in a bird feeder, and you won't have problems with birds for quite some time. It'll take care of the squirrels around your area as well.