Here is the full list of all 20 Birb Race achievements.
Win all field races
Win all island races
Win all cliff races
Win all cave races
Reach 50 meters in a run
Reach 100 meters in a run
Reach 150 meters in a run
Reach 200 meters in a run
Reach 300 meters in a run
Have a flight time of 50
Have a flight time of 150
Have a flight time of 250
Have a growth size of 25
Have a growth size of 50
Have a growth size of 100
Have 50 seeds at once
Have 250 seeds at once
Have 500 seeds at once
Have every Training & Race trophy