In this paper we introduce a novel engineering system for tracking animal movements. Study of animal movement has implications in several relevant and challenging research areas, i.e., from ornithology to global ecology and wildlife management. Inspired by the Internet-of-things vision, the proposed tracking system relies on GSM-based tracking devices that are directly connected to the GSM network to remotely transmit/exchange data with Application Servers/Cloud. The novel characteristic of the proposed GSM-based tracking system is the use of the GSM network for both localization and transmission. This allows to simplify the design of both hardware and software, hence reducing, size, weight and cost of the GSM-based tracking device as well as the fieldwork effort necessary to obtain tracking data. Moreover, this joint localization/transmission phase allows to reduce the energy consumption of the GSM-based tracking device, hence prolonging the life-time of the system and increasing the Quality-of-Service of the envisaged tracking application. We performed a detailed energy assessment of the GSM-based tracking device, while the whole GSM-based tracking system has been tested in a real deployment on four greater flamingos (Phoenicopterus roseus) for approximately 11 months in Northern Italy.