This paper presents the practical demonstration of a wireless sensor network (WSN) based on commercial nano-drones for structural integrity assessment of critical infrastructure. Leveraging the “Crazyflie 2.1” platform, each drone operates as a self-sustained sensor node equipped with vibration-sensing capabilities and an energy harvesting system. The proposed architecture supports dual-mode operation - flight and sensing - through a dual-MCU configuration that enables efficient power management and network integration. The system was validated on a full-scale damaged concrete bridge, where three drones were deployed to collect vibration data under operational conditions. Experimental results show strong agreement between the nano-drone measurements and those of benchmark commercial accelerometers, achieving a worst-case frequency identification error below 0.3 % and Modal Assurance Criterion (MAC) values above 0.93. These outcomes confirm the feasibility of using nano-UAVs for distributed modal analysis in vibration monitoring.