Panhandle, keep in mind back in the 60's waterfowl numbers were really low and a lot of banding activity went on (specifically 63-69). All of Texas falls in the Central Flyway. One of the things that was discovered through the banding research was that if you drew a line roughly at 100°Longitude, east and west of that line have VERY different waterfowl population dynamics. West of the 100° line the population nests in a different location, generally has higher nest success rate, and generally experiences lower harvest pressure, hince the creation of the "high plains mallard unit". And doesn't need the protection needed further east. The unit covers parts of several states. The USFWS doesn't allow much flxibiity on the HPMU, but it allows a long season anyway.
East of the 100° line the duck popuation is more stressed. It has recovered quite nicely. The split provides a refuge period, and allows duck numbers in an area to build back up. The timing of the split is based on water conditions, and historical arrival times of the birds. Keep in mind, as soon as you get into Oklahoma (and the Panhandle) the water actually freezes over in a pretty predicable pattern.
