Source: Cult of Cinders, pg(s). 81
Bidas magically pose as humanoids to infiltrate settlements, preferably those that control gold or coal mines which they can live in. Over weeks or months, they establish their importance in the settlement, until they become ready to reveal their terrible price: regular offerings of flesh and gold. The bida then moves to its lair and starts to grow fat from the regular sacrifices. To keep its secret, the bida hides the settlement from the outside world by concealing it in an illusion and demanding the residents destroy any roads connecting to it.
Bidas prefer the company of delicious food and only reluctantly tolerate other bidas. In rare cases, two bidas might conquer a settlement together, exploiting more wealth and food from the populace. Like most dragons, bidas are fond of treasure and gather vast hoards, usually from those whom they have cowed into submission.