content: What's on the 18th?   Look through the option on wikipedia and tell me what you think https://en.wikipedia.org/wiki/December_18 .   None of those really make sense, so the 18th was probably just the date where they started the series by posting a "Image depicting anticipation of a generic family get-together" on the 18th because it was one week before Christmas.    If you're more cynical then the images on the 18th were to commemorate "international migrants day" and the images on the 25th depict child refugee orphan penguins meeting their host family in their new country.  In which case you can expect the banners on the 31st to show grown-up penguins at a mosque in full-muslim attire listening to someone talking about exterminating the corrupt tropic-culture and spreading antarctia law, then on the 1st will be the aftermatch of a penguin suicide bombing.