Birds near small and great jets regularly rising (9)

'birds' is the definition.
(nightjar is a kind of bird)

'near small and great jets regularly rising' is the wordplay.
'near' becomes 'nigh' (similar in meaning).
'small' becomes 's' (abbreviation - e.g. clothes size).
'and' says to put letters next to each other.
'regularly' indicates alternate letters (regularly take one letter, leave next etc.).
'rising' says the letters should be written in reverse (going up in a down clue).
'great'+'jets'='greatjets'
The alternating letters of 'greatjets' are 'rajt'.
's'+'rajt'='srajt'
'srajt' written backwards gives 'tjars'.
'nigh'+'tjars'='NIGHTJARS'