It was a short silent animated film shown around Christmas time maybe 10 or 15 years ago. A planet, the inhabitants were going about their lives, working etc until they died. At this time they would walk to the centre of the planet, fall through and emerge from an umbilical cord type thing, reborn as a flying creature. These flying creatures were then killed by the inhabitants. It was a slow moving film with quite dark colours
“Skywhales” (9183)
http://www.imdb.com/title/tt0228867/?ref_=fn_al_tt_1
https://www.youtube.com/watch?v=qQ6qw1nh0tA&list=WL&index=13
YouTube link playing up but works on YouTube site (weird!)