Abstract: In some examples, a method for determining a communication structure to communicatively link a set of delivery unmanned aerial vehicles, UAVs, with a base unit, the communication structure defined by a minimum number of communication UAVs positioned relative to a set of delivery routes of the delivery UAVs at multiple transitory static positions, wherein a communication UAV at a transitory static position supports a communication region, comprises determining a subset of delivery UAVs outside of a communication region of a first communication UAV at a first transitory static position, the subset of delivery UAVs representing a number of unsupported delivery UAVs that are not communicatively linked, via the first communication UAV, to the base unit supplementing the number of communication UAVs with a second communication UAV, and selecting a second transitory static position for the second communication UAV, the second transitory static position minimising a metric representing a number of unsupported deliver