This paper describes the implementation and characterisation of a mobile ad-hoc network (MANET) of ultra-light intelligent flying robots. The flying nature of the network makes it suitable to collect or disseminate content in urban areas or challenging terrain, where line-of-sight connection between the Micro Air Vehicles (MAVs) allows for more efficient communication. Dynamic routing in the network enables the nodes to intelligently establish multi-hop routes to extend the communication range or to overcome obstacles. The presented MANET relies on the IEEE 802.11n WiFi standard for data communications and uses the OLSR routing protocol. Routing decisions based on dynamic link quality measurements allow the network to cope with the fast variability of the wireless channel and the high mobility of the MAVs. The implementation of such a system calls for the integration of advanced communication and control technologies in a very restrictive platform, be it in terms of weight, power consumption or availability of suitable off-the-shelf hardware. A detailed description of the system design is presented, and its performance is characterised based on in-flight network measurements. To the best of our knowledge, this is the first report of OLSR successfully tested in a MANET with such fast dynamics. We verify the trade-off between achievable throughput and the number of hops, and we report on the sensitivity of communication performance and routing behaviour to MAV orientation and flight path. Mitigation of such dependencies and improvements to the routing algorithm are discussed along with future research directions.