Common Redstart
Phoenicurus phoenicurus
The Common Redstart shows some affinity to the European Robin in many of its habits and actions. It has the same general carriage, and chat-like behaviour, and is the same length at 13–14.5 cm long but slightly slimmer and not quite as heavy, weighing 11–23 g. The orange-red tail, from which it and other redstarts get their names ("start" is an old word for "tail"), is frequently quivered. Among common European birds, only the black redstart (Phoenicurus ochruros) has a similarly coloured tail.
ID text from Wikipedia, CC BY-SA 4.0

Plumbeous Water Redstart
Phoenicurus fuliginosus
The plumbeous water redstart is typically 14 centimetres (5.5 in) long in total, with an average weight of 22 grams (0.78 oz) for males and 18.8 grams (0.66 oz) for females. The male birds are slate blue in colour with a tail that is rusty red. On the other hand, female birds are pale grey and feature a white rump.
ID text from Wikipedia, CC BY-SA 4.0
Where you might meet both
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Play today's Daily BirdPhotos and recordings are credited to their authors under the licence shown. Full profiles: Common Redstart and Plumbeous Water Redstart.