What substance is used to manage duck populations effectively?

Methyl anthranilate is used to manage duck populations effectively because it is a substance derived from natural sources, primarily grapes, that acts as a repellent. This compound has been shown to deter waterfowl without causing harm to them or the environment. Its utilization in managing duck populations is advantageous as it can control their presence in certain areas, thereby protecting aquatic ecosystems and preventing damage to crops or water resources.

The other substances mentioned do not effectively target duck populations. Glyphosate is an herbicide used primarily for weed control, chlorine is typically used as a disinfectant or sanitizer, and alum has applications in water treatment for its coagulating properties. None of these substances are used for the specific purpose of managing bird populations like methyl anthranilate is, which focuses on non-lethal approaches to deterring waterfowl in various settings.