Looking at N815AA, the most recent flights were:
DFW-SFO, ORD-DFW, LHR-ORD, ORD-LHR, DFW-ORD, CDG-DFW, DFW-CDG, ORD-DFW
For N810AN, its similar:
CUN-DFW, DFW-CUN, CUN-DFW, DFW-CUN, ORD-DFW, CUN-ORD, ORD-CUN, DFW-ORD, PEK-DFW, DFW-PEK, SFO-DFW
So it appears to be a mix of short domestics (utilisation/training) and then longer Internationals from major hubs.
Lovin' the smell of avgas in the morning....