In this paper we address the problem of efficiently securing multicast communication in energy constrained wireless ad hoc networks. We show that existing scalable key distribution techniques that rely on logical hierarchies, are energy inefficient. We show that great energy savings can occur when physical location information is considered in the key distribution scheme construction. We also show that even greater energy savings occur when routing and physical layer information is exploited. We develop a location-aware key distribution scheme, with the use of an iterative clustering algorithm. We formulate an optimization problem for the key distribution tree construction and maintenance and show that any candidate optimal solution does not scale with group size. We alternatively propose a heuristic routing-aware algorithm for efficiently constructing and maintaining the key distribution tree. We further improve our algorithm by incorporating batch rekeying instead of individual rekeying after every membership change. We present simulation studies that illustrate the improvements achieved using our algorithms.