The supply of energy to electronics is an imperative constraining factor to be considered during the design process of mobile ad hoc wireless sensor networks (MANETs). This influence is especially important when the MANET is deployed unattended or the wireless modules within the MANET are not easily accessible. Therefore, exploring novel sources of energy generation rather than operating electronics only on limited power supplies such as batteries is a major challenge. Monitoring free-ranging animal behavior is an application in which the entities (animals) within the MANET are not readily accessible; however, animal movement can be potentially used to generate energy. In this study, the head movements of individual sheep in a flock during grazing were monitored in order to investigate the amount of energy that can be generated by these movements. By applying the Lagrange–d’Alembert Principle to this problem, the equations of motion from each neck-mounted sensor as well as the amount of mechanical energy generated per time instant (each second) during upward and downward head movements were calculated. This resulted in the production of 857 mW and 1660 mW during the downward and upward movements, respectively. Furthermore, the energy consumption of each wireless node within the MANET was estimated to be 117.8 mW per second. Conversion of energy from mechanical to electrical requires miniature electromechanical generators that can currently provide between 25% and 50% conversion efficiency. Even using the worst conversion efficiency (25%), a minimum of 214 ± 25 mW of electrical energy per second could be generated. This amount exceeds the energy consumed by the wireless sensors that can be used to gather parameters describing animal behavior such as neck and head movement. This study suggests that the amount of energy generated by the vertical neck–head movement of sheep during grazing can be converted to useful electrical power adequate to provide power for operation of wireless sensor nodes on a continuous basis within a MANET-based animal behavior monitoring system.