The UAV Status widget shows you an overall summary of the states of the UAVs in the swarm. UAVs are sorted into four non-overlapping sets:
The first, green group corresponds to UAVs without any problem.
The second, blue group corresponds to UAVs with an info-level error code (e.g. initializing).
The third, yellow group corresponds to UAVs with a warning-level error code (e.g., low battery).
The fourth, red group corresponds to UAVs with severe/critical errors (e.g. GPS outage or compass error).
If you move your cursor over the widget, you get a tooltip that lists the physical IDs of all UAVs and the overall number of UAVs in a particular state, sorted by severity of states and error codes. Clicking on the widget itself reveals the UAVs panel of the main workbench area. Clicking on a row in the tooltip selects all UAVs in the corresponding state.