It is common that, for a given species, there be several populations which are catalogued as different subspecies. These often have some subtle differences between each other, but are quite hard to tell apart if you don’t know what you’re looking for. Nonetheless, this isn’t the case for the long-tailed tit.
This bird’s subspecies are sorted into three groupsLong-tailed Tit Identification, All About Birds, Cornell Lab of Ornithology:
Europaeus Group
A long-tailed tit of the europaeus group, ssp. taiti.
This group is found consistently across central and western Europe, barring the Italian Peninsula. It reaches up to western Türkiye and up to Poland, being sparsely found outside of these bounds. It’s also present on southern Japan and the Korean PeninsulaLong-tailed Tit (europaeus Group) - eBird.
In the Iberian Peninsula, its representative is the subspecies taiti, which can be found in the north half.
The description from this species’ page matches the birds in this group, where the biggest differences with subjects in other groups are its “eyebrows” and black back with white/rosy spots.
Alpinus Group
The alpinus group is found on the south half of the Iberian Peninsula, in some parts of the Italian Peninsula and around TürkiyeLong-tailed Tit (alpinus Group) - eBird. In the Iberian Peninsula, it’s represented by the irbii subspecies.
Adults in this group are similar to those of the europaeus group, sharing the black strips above the eyes. The biggest difference is the mantleThe back, between the wings. color. In this group, it’s gray, instead of black, and the pink areas are very small or absent altogether. Birds in this group also have a slightly shorter tail and, oftentimes, a black pach on their throat.
Caudatus group
An adult long-tailed tit of the caudatus group, ssp. caudatus.
Gegik, CC BY-SA 3.0, via Wikimedia CommonsThe third and most distinct group is the caudatus group. It lives in colder regions further up north: Scandinavia, Russia, and northern Japan (in particular, Hokkaidō). It’s not present in the Iberian Peninsula.
The main difference birds in this group have is their completely white head, unlike the other two groups. This has made the long-tailed tits in this group very popular in Japan and worldwide. In Japanese, they’re known as “シマエナガ (Shima enaga)”, lit. island + long-tailed tit島柄長 - Wiktionary, the free dictionary, given their presence only in Hokkaidō (the second largest island in Japan); on the other hand, the term “snow fairy” has become popular in English.
- ↑ The back, between the wings.