Total frequency of mon_bear spawns is 20 (This translates as a 2% chance as spawning). As time goes on the frequency falls like this 20/16/12/8/4. Now, the mon_zombear frequency scheme is 0/1/2/3/4. Only 4 points of mon_bear population are accounted for (and "replaced" with) zombified versions of them. So, 12 frequency points of mon_bear population are "lost". If this was an oversight and not an intentional design choice, one should redo whole mon_bear block to accommodate population leak:

        { "monster" : "mon_bear", "freq" :  4, "cost_multiplier" : 10,                "conditions" : ["SPRING", "SUMMER", "AUTUMN"] },
        { "monster" : "mon_bear", "freq" : 12, "cost_multiplier" : 10,                "conditions" : ["NIGHT", "SPRING", "SUMMER", "AUTUMN"] },
        { "monster" : "mon_bear", "freq" :  1, "cost_multiplier" : 10, "ends" :   72, "conditions" : ["SPRING", "SUMMER", "AUTUMN"] },
        { "monster" : "mon_bear", "freq" :  1, "cost_multiplier" : 10, "ends" :  168, "conditions" : ["NIGHT", "SPRING", "SUMMER", "AUTUMN"] },
        { "monster" : "mon_bear", "freq" :  1, "cost_multiplier" : 10, "ends" :  672, "conditions" : ["SPRING", "SUMMER", "AUTUMN"] },
        { "monster" : "mon_bear", "freq" :  1, "cost_multiplier" : 10, "ends" : 2160, "conditions" : ["SPRING", "SUMMER", "AUTUMN"] },