User blog comment:Lord Loss/Monster Hunter Theory... Blog/@comment-6050823-20130804200505

I know this maybe random but, they actually have reasons and explanations why some unusal monsters appeared in Moga Woods.

Great Wroggi and Wroggis: To expand their hunting territory and to find new feeding grounds.

Barroths: Some come do to long droughts in the Sandy Plains that causes their bogs to dry up in the summer heat.

Volvidon: Appears do to much higher insect populations during certain times in Moga.

Uragaan: There really isn't much about the Uragaan but, it seems the most likely reason is to gather plants and tree bark to make nest for their young and its also food for their young.

Duramboros: Seems to appear when large amounts plants grow in the spring season in the Deserted Island.

Besides these few I've found, there is no explanations for most of the other monsters.