On the Knights of Noromath server, enemy spawns are appearing according to several conditions. These include area, calendar, temperature, time of day, the frequency of creatures of their specific type, and some other circumstantial conditions.
Area - Any given area or environment type may be host to a particular sort of monsters or other creatures.
Calendar - Certain creatures are appearing in areas only during set times such as the full moon. For game purposes, the in-game day before and after the 15th of the month are considered to be the full moon.
Temperature - Certain creatures are drawn to seasonal changes in temperature but will appear out of season if the conditions warrant their early or late migration.
Time of Day - Diurnal, nocturnal, and less predictable spawn encounters are happening around the clock.
Frequency - The population and organization of particular creatures might call for gangs, packs, herds, etc. If the frequency of any particular creature deviates from tabletop conventions, it is purely campaign-specific.
Other Circumstances - In the case of Druidic Groves, the type of monsters encountered in an area around a grove is based upon the overall condition of that grove.