Delay-tolerant sensor networks (DTSNs) require efficient MAC transmission strategies that include energy constraint, relaxed latency, mobility support and diverse traffic load. Reservation-based and contention-based MAC schemes are used to improve throughput and energy consumption. In this paper, we propose a traffic adaptive, energy-efficient MAC protocol to achieve better data transmissions and as energy consumption, in order to satisfy the requirements in DTSN. In our protocol, reservation and contention modes are adjustable, in order to adapt to the traffic load with a suitable duty cycle length for achieving energy efficiency. The simulation results of our protocol demonstrate better performance in terms of energy efficiency and traffic adaptability than the schedule-based MAC protocol TDMA, the contention-based protocol CSMA, and the traffic adaptive protocol TRAMA under mobile DTSN environments.