Grey wagtail (Motacilla cinerea)

From Coloured illustrations of British birds, and their eggs . No copyright (public domain).

Looks like
The Grey Wagtail is a slender bird with a length of ca. 18 cm and has a long tail. Its back and head are grey, while its chest and underside are yellow. Its neck can be black (usually in males) or grey-white (usually in females). It has a pointy beak and feeds on insects and other small invertebrates. Στην περιοχή μας είναι επιδημητικό πουλί (δηλαδή βρίσκεται όλο το χρόνο) και φωλιάζει σε ρέματα και ποτάμια. Το χειμώνα συγκεντρώνονται πολλά άτομα μέσα στην πόλη. Μπορούμε να τα παρατηρήσουμε κυρίως σε δρόμους, πλατείες, ρεματιές, λιμάνια, αλλά και σε ταράτσες.
Where and when to spot it
In our area the Grey Wagtail is a permanent resident and can be seen all year. It nests near creeks and rivers. In winter, flocks of grey wagtail gather in the city, where we can observe them mainly on roads, on squares, in ravines, at harbours but also on rooftops.
Interesting facts
While sitting, it often wags its tail rhythmically (therefore its name), whereas during flight it shows a characteristic wavy flight pattern and calls a high tone.