Otherwise, its wings would freeze and broke or melted. This law was imposed by Queen Clarion, after Lord Milori break your wings. The fairies of the winter animals, sometimes help animals coming out of the ice and heat entering the refuge of fairies. Winter fairies take care of the animals in the Winter Woods. Some pets come in the winter, winning their coats and characteristics to live in the cold of winter woods.
When crossing the border, the animals gain characteristics of winter, for example: the squirrels gain a new coat, and rabbits too. Everything for them to stay in line with the winter weather. And the fairy of winter animals do the same, sending the animals to cross the border, the same waking from winter hibernation. Any other animal can also go to the winter woods, or go back to pixie hollow, without help. Some are afraid to go, and need help Fairies animals, and others are afraid to go back, and need the help of the fairies of the animals winter.
Frontier separates Pixie hollow, the Winter Woods. When animals come and go, everyone wins new features winter or hot seasons. No fairy risk losing his wings, both snow fairies and fairies warm seasons. In Secret of The Wings, and when accidentally froze pixie hollow, fairies winter had no problems getting through, just heat the fairies and animal heat had to hide during freezing. Because both worlds are hot, or too cold. An accident caused by device tinker, ended up being thrown in the river of the winter woods, and ended up creating a blizzard cold, going to pixie hollow, and consequently kill the pixie dust tree frozen and their dust would no longer flow, and no fairy could fly or use their magical talents.
The first to be hit by the cold, was the autumn forest, freezing the currency, and spreading throughout pixie hollow. But thanks to the cleverness of tinker bell, and courage frost fairies, managed to protect the Pixie Dust Tree, and everything returned to normal. Pixie Hollow melted the ice, and pixie dust began to flow in the tree and in the winter woods, and the boundary was back to normal. In Tinker Bell (2008) we see that some snow fairies go to the pixie dust tree, without having any problem with their wings.