Empty the bird feeder and bring inside.
Clean all the surfaces, inside and outside, with the glass cleanser and paper towels to remove any oil or grease from its surfaces.
Wash the bird feeder using dishwashing soap and warm water. Rinse well to remove all traces of the glass cleanser and soap.
Dry well using the paper towels.
Fill the crack with silicone caulk along the inside and outside of the crack. Use the putty knife to press the caulk into the crack.
Allow the caulk to dry and cure, following the manufacturer’s instructions. Scrape away any excess caulk using the putty knife.
Refill and rehang the bird feeder.