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

Cyanistes caeruleus

Regulus regulus

Erithacus rubecula

Chroicocephalus ridibundus

Phylloscopus trochilus

Lepus europaeus

Larus canus

Acrocephalus scirpaceus

Parus major

Phocoena phocoena

Troglodytes troglodytes

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