crepuscular

hämärä- Of or resembling twilight; dim.
puhekieltä active Active at or around dusk, dawn or twilight.
1999, J. Anne Helgren, Communicating with Your Cat, http://books.google.co.uk/books?id=lE-EbnD96QIC&pg=PA51&dq=%22cats+are+crepuscular%22&hl=en&sa=X&ei=Xw2eUsKFB8G3hQe5q4HICA&redir_esc=yv=onepage&q=%22cats%20are%20crepuscular%22&f=false page 51, ISBN 0764108557

That's why cats are crepuscular — most active at dawn and dusk — because mice and rats forage for food during these hours when fewer of their natural enemies are around.