While making a modpack of my own for a small group of friends and researching info about compatibility of mods and testing it on my own, it's become apparent that Chickens from this mod do not spawn in any biomes other than Vanilla biomes. When playing in a world with Lost Cities and Biomes O' Plenty, it proves nearly impossible to find the tier 1 chickens that cannot be bred. Would it be possible to add an option to un-restrict what biomes in the overworld / nether independently a chicken is able to spawn in, thus allowing them to spawn in ANY biome so long as the dimension is correct?

(Being able to whitelist specific biome ids/names would also be useful, although I understand that in particular would be asking quite a lot.)

This very much. I've looked into the code and the biome selection is based on hardcoded list of vanilla biomes. This is awful, please rewrite it into dynamic allocation based on Forge-declared biomes and their temperatures.

What mod & MC versions are you using? Its a bit harder to support modded biomes, but I have added some features into newest versions. but some things may not be working.

Also if you want to add in your own spawn controls. You can add a mod like InControl.

@Deuxis That is true for version 1.10 lower versions. But 1.11+ checks for biome types. It may not be ideal still, but it does work with modded biome's I have tested. While temperature may work, I have come across issues with that, when I worked on Enviromine. Also I dont work on 1.10, only versions going forward. This reason is because when I joined the team I was to only working on version past 1.10.