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

Turdus grayi

Melanerpes hoffmannii

Campylorhynchus capistratus

Psarocolius montezuma

Dives dives

Cyanocorax formosus

Amazilia rutila

Eumomota superciliosa

Thraupis episcopus

Tyrannus melancholicus

Patagioenas flavirostris

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