I researched the making of bal-chatri traps when in high school, thinking I wanted to become a falconer and (Idaho) state laws dictated that this was the only permitted method for capturing a kestrel, the only raptor permitted to be captured by apprentice falconers, contingent upon having state-approved quarters and knowledge of care and feeding for said bird. Life intervened, and I haven't yet fulfilled this dream, many years and many states of residence later.
(n): a type of trap designed to snare raptors (birds of prey) for banding and study by scientists, or to capture birds for falconers, the practitioners of falconry. The original traps, developed in India, consisted of a wire cage, with one or more small lure birds trapped within, festooned with horsehair nooses affixed to the wires of the cage such that a hawk or falcon landing on the trap would become ensnared.
Also known previously (1897) as a Shikra trap, and more recently spelled ball-chatri or ballchatri by English speakers and writers ignorant of, or unaccepting of, the standard transliteration of established foreign spellings and terms.