Wireless Sensor Networks (WSNs) are networks formed by highly constrained devices that communicate measured environmental data using low-power wireless transmissions. The increase of spectrum utilization in non-licensed bands along with the reduced power used by these nodes is expected to cause high interference problems in WSNs. Therefore, the design of new dynamic spectrum access techniques specifically tailored to these networks plays an important role for their future development. This work aims to provide insights into the performance of two well-known low energy-consuming Medium Access Control (MAC) techniques for WSNs (the receiver-initiated and the short-preamble burst), adapted to work with multiple channels. The results obtained show the best working conditions for each approach.