Maybe they can't fly, but they sure can swim. Reindeerswim strongly across rough, wide rivers and icy expanses of ocean, up to six miles per hour. And, within 90 minutes of being born, a baby reindeer can run. Within a few hours, it is able to run several miles.
Female reindeer have antlers too.
You probably already knew that Rudolph was not originally part of Santa's team...