Wireless Sensor Networks are constrained by limited energy sources, limited processing capabilities, densely deployed nodes, unreliable and asymmetric wireless links, and limited bandwidth. Under all these constraints, performance of Wireless Sensor Networks essentially depends upon proper selection of routing protocols among variety of existing protocols. In this paper, performance of Dynamic Source Routing protocol (DSR), Ad hoc On Demand Distance Vector Routing protocol (AODV), Zone Routing Protocol (ZRP), and Optimized Link State Routing Protocol (OLSR) have been evaluated for a wireless ad hoc sensor network on the basis of performance metrics, such as energy consumption of sensor nodes, total number of packet collisions, total number of error packets, total overhead transmissions, and throughput of Wireless Sensor Networks. The simulation results show that OLSR protocol being pro-active in nature least performs, while on the other hand, DSR protocol performances quite well in terms of energy consumption of sensor nodes, total number of packet collisions, total number of error packets, and total overhead transmissions. But in terms of network throughput, ZRP protocol performs very well followed by OLSR, DSR, and AODV. Finally, after taking into consideration of all major constraints of Wireless Sensor Networks, it is recommended that DSR protocol is a highly energy efficient, spectrally efficient, and reliable protocol for ensuring error free and congestion free delivery of sensed data packets.