( It ( ( is ( important ( to ( stay ( at ( that ( body weight ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (PRP It)) (VP (VBZ is) (ADJP (JJ important) (S (VP (TO to) (VP (VB stay) (PP (IN at) (NP (DT that) (NN body) (NN weight)))))))) (. .)))
It is important to stay at that body weight.
(ROOT (S (NP (NNP Birds)) (VP (VBP need) (NP (DT a) (JJ light-weight) (NN body)) (PP (IN for)) (S (VP (TO to) (VP (VB stay) (ADVP (RB aloft)))))) (. .)))