I want to know the answer to the following question:
For what reason would birds mor far beyond the normal range?
All the background I'm provided with is that "Bohemian waxwings Bombycilla garrulus well show this unpredictable variation in annual numbers, with five major arrivals in Britain during the nineteenth century, but 18 between the years 1937 and 2000.". Is that enough to answer the question?