
These are species with at least one recorded territory in Belize, not a national checklist: a bird list from eBird or Avibase is more complete. The counts follow recording effort as much as wildlife, so a country with more visitors and more naturalists will show more of both.
The species with the most open occurrence records in Belize, among those a photograph exists for. Most recorded is not most numerous: it rewards animals that are common, conspicuous and live where people go.

Myiozetetes similis

Dives dives

Sporophila morelleti

Cyanocorax morio

Amazilia tzacatl

Pitangus sulphuratus

Pheugopedius maculipectus

Melanerpes aurifrons

Quiscalus mexicanus

Turdus grayi

Eupsittula nana

Amazona autumnalis
The reference database has no regions filed under Belize.
The field guide covers Belize on the map, but none of its species have an entry written for them yet.