When I was in bio 101 we did an experiment where we fed cabbage leaves to Bertha Army Worms (kind of caterpillar). Some of the leaves were treated with an extract of tobacco. The worms ate the untreated leaves just fine, but when we introduced the bits of cabbage soaked in tobacco water, they would take a bite, and…

Birds are smart, but not smart enough to reason that a smelly brown butt will keep the bugs out of a nest. They just use what they can find.