This paper investigates the efficient deployment and mobility of multiple unmanned aerial vehicles (UAVs) as aerial base stations to collect data from ground Internet of Things (IoT) devices. The main contributions include a novel framework for jointly optimizing the 3D placement and mobility of UAVs, device-UAV association, and uplink power control to minimize the total transmit power of IoT devices. The proposed approach involves two key steps: first, determining the optimal UAV locations and associations given the locations of active IoT devices; second, analyzing the UAV mobility patterns to dynamically serve the IoT devices over time. The optimal 3D trajectory of each UAV is derived to minimize the total energy used for mobility while ensuring reliable uplink communications. Simulation results show that the proposed approach reduces the total transmit power of IoT devices by 45% compared to stationary aerial base stations and enhances system reliability by up to 28%. The results also reveal a tradeoff between the number of update times, UAV mobility, and IoT device transmit power.This paper investigates the efficient deployment and mobility of multiple unmanned aerial vehicles (UAVs) as aerial base stations to collect data from ground Internet of Things (IoT) devices. The main contributions include a novel framework for jointly optimizing the 3D placement and mobility of UAVs, device-UAV association, and uplink power control to minimize the total transmit power of IoT devices. The proposed approach involves two key steps: first, determining the optimal UAV locations and associations given the locations of active IoT devices; second, analyzing the UAV mobility patterns to dynamically serve the IoT devices over time. The optimal 3D trajectory of each UAV is derived to minimize the total energy used for mobility while ensuring reliable uplink communications. Simulation results show that the proposed approach reduces the total transmit power of IoT devices by 45% compared to stationary aerial base stations and enhances system reliability by up to 28%. The results also reveal a tradeoff between the number of update times, UAV mobility, and IoT device transmit power.