Question

Read the following passage and answer the question. When rangers in the Kaziranga grasslands began testing acoustic sensors last year, they were not looking for poachers first. They were listening for silence. In stretches where the sensors recorded fewer bird calls at dawn, camera traps later confirmed the pattern: tiger movement had shifted, and with it the behaviour of prey species. The team, a mix of forest officials and data scientists, fed three years of sound recordings, GPS-collar pings and rainfall data into a model that now predicts, with surprising accuracy, where herds will graze a week in advance. Poaching incidents in the pilot zone fell by nearly a third, not because patrols multiplied but because they reached vulnerable spots before the poachers did. Critics caution that the system is only as honest as its training data; a sensor network concentrated near roads, they argue, teaches the model that the forest ends where the asphalt begins. The rangers concede the point and are now deploying solar-powered units deeper into the core zone. Their larger claim, however, stands: conservation, long guided by instinct and anecdote, is learning to listen at scale. What were the rangers primarily trying to detect when the acoustic sensors were first deployed?