It's difficult for wild animals to hunt for their food in wi

如上所诉,整个是以it做形式主语,代替to hunt for their food ,
顺便说下,这里没有从句.（因为从句也是独立句子,至少要有主谓成分）
这里有的是to hunt for their food (动词不定式短语),
because of the weather（原因状语）
in winter (时间状语)
不要混淆短语和从句的概念