Why do birds have short necks? pls help :/

Most diving birds have (relatively) long necks and shorts legs, although their necks aren't as long as say herons, storks or egrets. Take the common loon for instance. Their necks can be up to half as long as their bodies but their legs are so short and set so far back that they are very awkward on land.

x would be the most and the least would be y because there are more fruit   and seeds than flock z has insects