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

Hirundo rustica

Acrocephalus scirpaceus

Sylvia atricapilla

Erithacus rubecula

Cyanistes caeruleus

Phylloscopus collybita

Parus major

Acrocephalus palustris

Prunella modularis

Emberiza schoeniclus

Fringilla coelebs

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