Birds are creatures of habit, keenly aware of their environment. They are intimately familiar with their surroundings, and respond quickly to both positive and negative changes in their world.
To take advantage of that, nerve and intestinal irritants create a change in the birds’ habits after several exposures, because their nervous or intestinal systems are in a state of distress. When the offending birds’ nesting, feeding or roosting areas are treated with nerve or intestinal irritants, their sense of security is destroyed and the process of breaking their attachment to the area begins.
With several exposures, the offending birds completely lose their feeling of security and begin to seek other, less-stressful locations for nesting, feeding or roosting.
from Pest Management Professional https://www.mypmp.net/2019/02/11/break-birds-sense-of-security/