By davidrasmus / Getty Images As winter approaches, many of us are tempted to hole up at home like a bear in its den. But hibernation is about more than just getting snug and not going out: bears must prepare themselves by building up huge fat reserves. This process is the focus of Fat Bear Week, an autumn trend not just out in nature but also on the web. As winter approaches, many of us are tempted to hole up at home like a bear in its den. But hibernation is about more than just getting snug and not going out: bears must prepare themselves by building up huge fat reserves. This process is th…