What are the most important birding sites to visit in a birding tour in Sri Lanka?

If your main focus is to watch all 33 endemics, here are my top birding sites for endemic birds in Sri Lanka:

1. Horton Plains
2. Kitulgala Rain Forest
3. Nuwara Eliya
4. Sinharaja Rain Forest
5. Yala National Park

Other than the sites listed above, there are many good birding sites all over Sri Lanka that would suffice a general bird watching tour. If you are coming to see a specific non-endemic bird you may have missed in a previous tour, you may need to go to a certain site in Sri Lanka not in the list for endemic birds.

Here is my most visited or famous birding sites list for a general birding tour:

1. Anawilundawa Ramsar Wetland
2. Bundala Ramsar Wetland and National Park
3. Chundikullam Bird Sanctuary
4. Jaffa cost way and lagoon areas
5. Kaudulla National Park
6. Kumana National Park (East of Yala)
7. Mannar area
8. Minneriya National Park
9. Sigiriya Forest Reserve
10. Surrey Bird Sanctuary
11. Udawatta Kele Forest Reserve

For more info see Walk With Jith's Birding Tours in Sri Lanka.