A bulletin board that shows which animals hibernate can be educational (and fun) in many ways. Depending on your location, you may wish to adjust the list to reflect local animals. For example, some of the common animals that hibernate in the northeastern part of the United States are bears, skunks, chipmunks, bats, groundhogs and raccoons. You can also use this bulletin board to teach about habitat by creating "doors" to open for children to discover which animal goes to hibernate in a particular location. For example, a rock face with a small crack in it could open up and reveal a sleeping bear inside. A hole in a tree could be opened to reveal a raccoon.
If you wish to go even deeper into your science lesson, you can chart the different ways animals hibernate. Some animals, such as bears, keep their bodies very warm with stores of fat so they can wake up and move quickly if they need to. Others, like chipmunks, skunks and raccoons, wake up frequently during the winter to get food if the weather gets warmer. Still others, such as some kinds of bats, have such a low body temperature it is hard to tell whether they are alive. A bulletin board that illustrates this concept might involve one of the simple graphs that your preschoolers have learned to use. You can place pictures of each animal next to the way that they hibernate and have students count which way most of the animals hibernate.
There are many excellent books about hibernation for young children, and no doubt you have many of them prepared to read for your class. You can create a bulletin board with the books that you have read (or plan to read) about hibernation. When you finish all the books, the children can make themselves little paper bears or other hibernating animals with their names on them and post their pictures next to their favorite books.
If you wish to go more in depth into the habits of only one animal, the bear is a popular choice for teaching preschoolers about hibernation. However, if your students have different interests (perhaps a skunk resides under someone's porch or a raccoon frequents the playground) you should tailor the animal of your focus to your class. In this case, you could create a large picture of the animal. Students can decorate the board with the animal's preferred bedding (most likely "leaves" made of paper) and a store of food if the animal is one that stocks food. Then you can put the animal on its bed and put it to sleep there for the winter. Students can collect facts to put on the board during the unit.