A data collection system (1) for monitoring the behaviour and states of a plurality of animals (2) comprises providing the animals (2) with respective monitoring devices (4) for monitoring the behaviour and states of the animals (2). A drone (7) comprising a mobile data collection device (5) secured thereto is configured to fly past the animals (2) at predefined data collection time intervals, typically of six hourly intervals. Each mobile data collection device (5) comprises a first secondary communications module (15) for wirelessly communicating with a second secondary communications module (32) located in the respective monitoring devices (4) for uploading data indicative of the behaviour and states of the animals (2) to a microcontroller (8) in the mobile data collection device (5). The uploaded data indicative of the behaviour and states of the respective animals (2) is written to and stored in a primary memory (17) of the mobile data collection device (5). A primary communications module (10) in the mo
