We propose application of Opportunistic Resource Utilization Networks (Oppnets), a novel type of Mobile Ad Hoc NETworks (MANETs), for ad hoc networking of Unmanned Aerial Vehicles (UAVs) in surveillance missions. Oppnets provide effective resource virtualization and adaption to highly dynamic and unstable nature of MANETs. They can be viewed as middleware to facilitate building flexible and adaptive distributed systems that provide all kinds of resources or services to the requesting application via the so called helper mechanism. The simulation study focuses on the impact of an initial target position on the performance of Oppnet-based UAV surveillance systems. We find that detection success ratios and time to detect a target are negligibly affected by the initial target position in the surveillance area when UAVs expand up their Oppnet quickly, but strongly affected by the initial target position when UAVs are slow in building up their Oppnet.