The correct answer is option 4: Ornithology. Ornithology is the scientific study of birds. It involves researching and studying various aspects of birds including their anatomy, behavior, ecology, and evolution. Ornithologists study bird species from all over the world and use various methods such as field observations, laboratory experiments, and data analysis to gather information and gain insights into the lives of birds. They may also specialize in specific areas such as bird migration, bird conservation, or bird vocalizations. Limnology (option 1) is the study of freshwater ecosystems, Herpetology (option 2) is the study of reptiles and amphibians, and Malacology (option 3) is the study of mollusks.