176. FILL IN THE VOWELS

Lines to an owl:—

HNLDTWRSTHGLMWL
THLVSTTHTTHLVSTTHWL
RNLDKSRHLLWTN
SLSTSSLMNSNDSLN
SMRNFLNNLVSTG
RFRHTNGHWLSTKNW

As a hint, the last line is:—

Or of your hooting howls to know.