Christine, your books are correct that Red-backed Shrike breeds across Europe and only as far east as Xinjiang. It is a declining species in much of the range, but is still numerous across most of the range. The species is a long-distance migrant, wintering in Africa.
Like many birds, some individuals occasionally go 'the wrong way' and turn up in unexpected places. This is the case with this bird - although Red-backed shrike is not normally seen in HK, occasional individuals do turn up. I think this is the 5th to be recorded in HK so far. There are also records from other parts of East Asia (Taiwan, Korea, Japan).
Most birds turning up out of range in this way will be juveniles/first winter, because the adults have already made the migration and will know which way to go, whereas the young birds are making their first migration and are more likely to make a mistake.
