Beaver Privacy

Trying to do the Adoption campaign in ZT2, with cheetahs, beavers, hippos, and.. ibex? Anyways, I can't release my beavers because their privacy is critical. I know they have to build their own lodge with branches.. I gave them branches as soon as the enclosure was set up.. they never built a lodge. Is there a known issue with this? Thoughts? Cheers