  Zonal flows are recognised to play a crucial role for magnetised plasma
confinement. The genesis of these flows out of turbulent fluctuations is
therefore of significant interest. We investigate the relative importance of
zonal flow generation mechanisms via the Reynolds stress, Maxwell stress, and
geodesic acoustic mode (GAM) transfer in drift-Alfv\'en turbulence. By means of
numerical computations we quantify the energy transfer into zonal flows owing
to each of these effects. The importance of the three driving ingredients in
electrostatic and electromagnetic turbulence for conditions relevant to the
edge of fusion devices is revealed for a broad range of parameters. The
Reynolds stress is found to provide a flow drive, while the electromagnetic
Maxwell stress is in the cases considered a sink for the flow energy. In the
limit of high plasma beta, where electromagnetic effects and Alfv\'en dynamics
are important, the Maxwell stress is found to cancel the Reynolds stress to a
high degree. The geodesic oscillations, related to equilibrium pressure profile
modifications due to poloidally asymmetric transport, can act as both sinks as
drive terms, depending on the parameter regime. For high beta cases the GAMs
are the main drive of the flow. This is also reflected in the frequency
dependence of the flow, showing a distinct peak at the GAM frequency in that
regime.
