Brooke's early work with birds focussed the taxonomy of the swifts (Apodidae) of the Old World. Soon he acquired a solid background and became a world expert on the topic. Besides a wide range of papers he proposed new subspecies of the palm swifts, of mottled and African swift and introduced the genus Hydrochous.[1]
Already 1971 Brooke served as a member of a panel of four specialists dealing with the birds of Zambia. Later, in particular after he joined the Percy FitzPatrick Institute, he widened his field of expertise, especially regarding the taxonomy and other biological aspects of various seabird groups. One of his major works is the "South African red data book – birds", for which he was awarded the Gill Memorial Medal.[1]
One of his last papers reflect his findings on the possible difference of the South African pied avocet, which he thought was a distinct subspecies. However, due to the limited available material he did not give it a scientific name.[1]