Surveillance data generated by the nodes of a wireless ad-hoc (multihop) sensor network is aggregated at local sinks and forwarded to a central node. The number of sensor nodes that the sinks can support determines a "capacity" of the network. The number of surveillance data flows (each emanating from a sensor node) that a node can relay is limited by a variety of factors such as channel conditions (including interference, attenuation, fading and ambient noise) and internal hardware and energy resources of the node. Assuming that the one-hop neighbors of a sink form the most significant communication relaying bottleneck, we analytically determine the fraction of sensor nodes that are unable to connect to their sink, i.e., the outage probability. This expression is numerically evaluated and its accuracy is assessed and reported in a preliminary simulation study.