Yes they are consumers. They must eat food to obtain energy. They cannot produce their own energy. They are mostly plant eating animals so they are in the middle of the food chain. Photosynthetic organisms that produce their own food are at the bottom and there are several levels of consumers which eat either producers or other consumers. Since caribou eat mostly plants (although there is some evidence that they may eat small animals.) and they have some preditors they would be in the middle of the food chain.