( ( The bird ) ( ( ( stays aloft ) ( for ( ( 2 hours ) ( until ( ( the trains ) pass ) ) ) ) ) . ) )
(ROOT (S (NP (DT The) (NN bird)) (VP (VBZ stays) (ADVP (RB aloft)) (PP (IN for) (NP (NP (CD 2) (NNS hours)) (SBAR (IN until) (S (NP (DT the) (NNS trains)) (VP (VBP pass))))))) (. .)))
The bird stays aloft for 2 hours until the trains pass.
(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)))))) (. .)))