Seeing as I'm such a Ga'hoole nut, and I happen to own A Guide Book to The Great Tree, I decided to write down all the holidays celebrated at the Great Tree on our own calendar.

Egg Festival - March 20 Edit

This minor festival takes place on what we call the vernal equinox. Owls from all kingdoms celebrate the beginning of spring and the many eggs the season brings with it. Some owls put egg-shaped stones in the nest for good luck, and when the moon rises expectant parents hoot and screech with all the other owls in the tree. 

Nimsy Night - June 20 Edit

This holiday takes place on the summer solstice. It is the shortest night of the year, and classes are cut short and owls have as much fun as possible, welcoming the steadily growing nights. The Tree is decorated with all things green, some of the owls donning green as well. Owls also harvest herbs to be dries, and have a feast. They traditionally have a "snake bake", feasting on escargot. 

Moon Festival - August 18 Edit

This festival takes place on the eighth full moon of the year, when it's said to be its brightest. The owls tell a legend; There was once three moons in the sky, and an aging, Vilis, envied the youth and speed or younger owls. Vilis went to a magical spider, Zuzanna, who gave him an elixir that gave him the strength of a thousand owls. He flew up to the moons and plunged two into the sea to pay back Zuzanna, making the night dark. However, his mate, Ilona, grew jealous of his strength, and drank some of the elixir, and ended up stuck on the moon. Zuzanna granted Vilis to visit his mate once a year, and on this night the moon shines the brightest.

Milkberry Harvest Festival - September 22 Edit

This festival takes place on the autumnal equinox, and is well documented in The Rescue. All chaw classes are cancelled for seven days to harvest the Milkberries, and all manner of Milkberry treats are eaten. Owls also have dances, and drink Milkberry wine.

Punkie Night - October 1 Edit

This celebration takes place on the first new moon after the Milkberry festival. Owlets make masks that resemble other species of owls and birds, and go from hollow to hollow performing tricks, singing and telling jokes in exchange for treats, called galooshing. Owlets play games like blooking for milkberries (the owl equivalent of bobbing for apples) and play tricks on older owls, such as putting tree sap in their nests.

Balefire Night - Mid-November Edit

The exact date of this festival isn't verified, it simply takes place at the end of Autumn. (It could well be based off the British holiday Bonfire Night, which takes place on November 4.) Owls of the Great Tree make a large bonfire on the beach, and fly around it, testing out their flying skills on the strong updrafts. Only cooked food is eaten on this night, seeing as it celebrates how the Guardians learned to utilize fire. There are competitions in hunting and flying, and at the end of the night the embers are taken to the forge. 

Founder's Night - December 22 Edit

Also known as Long Night, this holiday takes place on the winter solstice, the longest night of the year. Said to be the biggest celebration of the year, with flying contests, where the winner is crowned with wreaths made from vines. There is a hunting contest, and then a great feast is held and the owls share the prey from the hunting contest.