The population of the hive is beginning to decrease; older bees that die off are not replaced in the same numbers by the new brood. Drones are being removed in numbers from the hives by the workers to conserve winter stores. Nectar and pollen sources are becoming more scarce as the cooler weather moves in and plants begin to die off or go dormant.
The worker bees will begin to bring in large amounts of propolis to seal the hive against drafts for the winter and on cold nights they will begin to cluster inside the hive. There may be intense robbing activity if you have a weak hive in your apiary - take steps to equalize colonies or prevent robbing.
Remove all honey supers before the end of the month (if not sooner) to allow the bees to fill the brood chambers with the winter honey/pollen stores.
You have a lot to do this month. First, you should be pulling off all honey supers and either securely storing them or extracting them. This will prevent the bees from wasting nectar/energy filling a super/frames incompletely and allows them to build up their stores for winter survival.
Secondly, you should check your hive for honey stores; if the hive does not feel heavy or the bottom brood supers are not (75- 80%) full of honey you will need to consider feeding them. A 2:1 ratio (sugar/water) is used in the fall to assist the bees in dehydrating the syrup.
Thirdly, treat for mites - both tracheal and varroa. This is the best time as the colony is going broodless and any mites present will be exposed to your removal method. Also, treat for diseases such as foulbrood or nosema.
Fourthly, ensure that your hive has adequate ventilation for the winter - a lack of ventilation can result in a build-up of moisture which can then condense on the inner cover and then turn cold and drop back onto the colony chilling and possibly killing them. Too much moisture can also result in mildew, and mold and possibly spoil any uncapped honey stores.
Lastly, protect the hive from the worst of wind and snow/rain to help the colony maintain the temperature in the cluster.