" Later (swifts) gather higher in the sky...And then, all at once, as if summoned by a call or a bell, they rise higher and higher until they disappear from view. These ascents are called vesper flights....Vespers are evening devotional prayers, the last and the most solemn of the day, and I have always thought 'vesper flights' the most beautiful phrase, an ever-falling blue. "

― Helen Macdonald , Vesper Flights