To finish the caucus race, you have to:
Attract all wildlife from 'A Caucus Race' (mouse, dodo, lory) 10 or more times in your garden
Spot all wildlife from 'A Caucus Race' (mouse, dodo, lory) 3 or more times in other gardens
The amount of Alice helpers you attract or spot don't count since they only give you hints for your cards.
For more information there is a thread that explains the challenge in detail:
https://www.fairylandgame.com/fbfairy/forums.php?tid=171905