Board Game Arena

In my current game (Table #268972330) I just scored a card by discarding a card and then moving two animals. Neither of the animals I moved was onto a bird space (but I had a matching animal already on the space). I was awarded a bird card at the end of the turn, and I have ZERO idea why.

Is there an additional way to earn birds that isn't in the rules? Is this a bug? If it is a bug I'll happily submit it!

It was at Move #96 (or just before!)

Some of the goal cards also award a bird token when completed, it's just really small and hard to see on the card. If you have a look at your current Sheep-Pig-Sheep card at the bottom centre on the arrows is a tiny little bird token.