( ( Having ( ( the ( largest ( wingspan-to-body-weight ratio ) ) ) ( of ( any bird ) ) ) ) ( , ( they ( ( are ( ( ( ( ( essentially aerial ) , ) ( able ( to ( ( stay aloft ) ( for ( long periods ) ) ) ) ) ) , ) ( ( landing only ) ( to ( ( ( roost or ) breed ) ( on ( ( trees or ) cliffs ) ) ) ) ) ) ) . ) ) ) )
(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) (NP (NP (RB essentially) (JJ aerial)) (, ,) (ADJP (JJ able) (S (VP (TO to) (VP (VB stay) (ADVP (RB aloft)) (PP (IN for) (NP (JJ long) (NNS periods))))))) (, ,) (VP (VBG landing) (ADVP (RB only)) (S (VP (TO to) (VP (VB roost) (CC or) (VB breed) (PP (IN on) (NP (NNS trees) (CC or) (NNS cliffs))))))))) (. .)))
Having the largest wingspan-to-body-weight ratio of any bird, they are essentially aerial, able to stay aloft for long periods, landing only to roost or breed on trees or cliffs.
(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)))))) (. .)))