User blog comment:Lord Loss/Monster Hunter Theory... Blog/@comment-6050823-20131128025834

Since there is no explanation behind why some of the monsters in the Unknown Great Forest appear in the area, here is my theorys behind afew of them.

Gravios and Black Gravios: To me, they most likely appear for three reasons. To have their young(The Basarios in MH4 can only be found in the UGF), they may cross between the UGF to get to the Primeval Forest and the Underground Volcano, and are possibly Basarios that recently became adults.

Nerusukyura: Since they are known to wander in some unusual areas, I'm guessing sometimes they cross between this area to get Primeval Forest or the Underground Caves and, some may even live in the temples in the area.

Zinogre and Stygian Zinogre: Since their is a forest in the Heavenly Mountains(Assuming they are the same forest), I guess Zinogre may occasionally go into the forest to hunt, if food is scarces in the mountains. Another thing I've been thinking about is what if some of the Dragcophage Bugs attract them to the forest during certain seasons, since both can be found living in both the Heavenly Mountains and the Unknown Great Forest and, since it hasn't been confirmed that Stygian I its own species.

Teostra and Kushala Daora: With both of them, I can picture them coming to this area to hunt from it being rich with prey. If Lunstra was around, I could picture her coming here to make her nest or atleast gather materials for bher nest.

Prey Packs: Gendrome and its pack may come here during the time the Volcano becomes active in the Underground Volcano. Iodrome and its pack could just live in the UGF and, come to the Underground Volcano during certain seasons.

Aruserutasu and Generu Seruatasu: I think its possible that their species mates in this area and possibly even lay eggs in this area. Also, if any wonders how Generu gets to the UGF, she either burrows their are just lets tan Aruserutasu carry her there.

Brachydios: I think its possible that it just hunts in this area, when food is scarces but I think it also lives in this area, when the volcano is dormant and most competition is still in the area.