
These are species with at least one recorded territory in Guatemala, 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 Guatemala, among those a photograph exists for. Most recorded is not most numerous: it rewards animals that are common, conspicuous and live where people go.

Dives dives

Turdus grayi

Quiscalus mexicanus

Melanerpes aurifrons

Myiozetetes similis

Sporophila morelleti

Saltator atriceps

Cyanocorax morio

Thraupis abbas

Pheugopedius maculipectus

Campylorhynchus zonatus

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