We present an integrated approach for supporting in-network sensor data processing in dynamic and heteroge- neous sensor networks. The concept relies on data stream processing techniques that define and optimize the distribution of queries and their operators. We anticipate a high degree of dynamics in the network, which can for example be expected in the case of wildlife monitoring applications. The distribution of operators to individual nodes demands system level capabilities not available in current sensor node operating systems. In particular, we present a system for seamless and on demand operator migration between sensor nodes. Our framework, which we implemented for Contiki running on TelosB nodes, supports stateful module migration including selected parts of the code and data sections.