Unique Tribe Cultures: Your Birbbers culture can be completely designed from the ground up in what you see fit. If you want to make a society of Cannibalistic Birbbers, go ahead. If you want to make a peaceful society that venerates a god or goddess that could snuff them out in a single show of violence, you can as well!
Post-Apocalyptic Survival: As such, tribal societies in the wasteland can be vicious, just remember that! Using human technology is beyond their comprehension but can still be referenced.
Real-Life References: Misuse of sacred, religious or important symbols, clothing, items should be avoided. While being inspired with real-life examples as inspiration, please be rational. If there is a Birbber with such elements, politely ask someone to change it (disrespectful behaviour and callout posting will not be allowed, ever) When people copy an artwork without permission or attribution, it can profoundly harm artists and denigrate the meaning of their imagery and its cultural significance.