Help for bird species

Good morning, I'm new to the forum and would like to thank you in advance for your attention. I work for an Italian software house and  we have started working on a new project: a bird watching simulation game which will be released on mobile platforms by the end this year. Our goal is to provide the users with the best reproduction of some of the most famous bird watching scenarios to be found on our planet. Due to it's importance, we have decided to include Minsmere RSPB in our simulation. For this purpose, we are selecting different bird species that can be observed in the park and would be glad if you could help us in this task. Our aim is to provide the user with the real difficulties that may occur in sightings, by selecting a total of 25 different bird species divided in 5 different rarity categories (from the most common to the rarest). For every bird our graphic department will provide a 3d modelling.
We would really appreciate anyone's help.
Thank you in advance