( ( Having ( ( the ( largest ( wingspan-to-body-weight ratio ) ) ) ( of ( any bird ) ) ) ) ( , ( they ( ( ( ( are ( essentially aerial ) ) , ) ( able ( to ( ( ( stay aloft ) ( for ( more ( than a ) ) ) ) week ) ) ) ) . ) ) ) )
(ROOT (S (S (VP (VBG Having) (NP (NP (DT the) (JJS largest) (JJ wingspan-to-body-weight) (NN ratio)) (PP (IN of) (NP (DT any) (NN bird)))))) (, ,) (NP (PRP they)) (VP (VBP are) (ADJP (RB essentially) (JJ aerial)) (, ,) (S (ADJP (JJ able) (S (VP (TO to) (VP (VB stay) (ADVP (RB aloft)) (PP (IN for) (NP (QP (JJR more) (IN than) (DT a)))) (NP (NN week)))))))) (. .)))
Having the largest wingspan-to-body-weight ratio of any bird, they are essentially aerial, able to stay aloft for more than a week.
(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)))))) (. .)))