Billie doesn't notice at first. That they have magical extensions of their souls or whatever in the form of birds, that's a new enough concept that she misses it until after she's given Daud a nod and looked back out the outpost window, towards the bonfires. It's only when Deidre makes an offended noise from where she's huddled up, against Billie's neck for warmth, that she looks back.

There should be two birds in here, she realizes.

"Did you forget your feather duster somewhere?"

It's definitely too cold for him to have left her out there.