Bird Proof Bird Repellent liquid is a non-toxic viscous sticky liquid chemical that makes a surface tacky and uncomfortable to birds. Birds avoid Bird Proof like humans avoid wet tar. Although it is non-toxic and non-lethal its “feel” is extremely irritating to roosting birds. Protect your property from the annoyance mess and constant clean-up that pest birds cause. It s the easiest way to bird-proof open or recessed areas and hide-away corners. Use a discharge pressure of 40 psi. One gallon covers up to 120 square feet or an average tree with a 5″ diameter trunk.