( ( Whereas ( gliders ( need ( thermals ( to ( stay aloft ) ) ) ) ) ) ( , ( balloons ( ( need ( ( ( calm ( , stable ) ) conditions ) ( with ( ( ( ( ( no up ) draughts ) and ) ( generally light ) ) winds ) ) ) ) . ) ) ) )
(ROOT (S (SBAR (IN Whereas) (S (NP (NNS gliders)) (VP (VBP need) (S (NP (NNS thermals)) (VP (TO to) (VP (VB stay) (ADVP (RB aloft)))))))) (, ,) (NP (NNS balloons)) (VP (VBP need) (NP (NP (ADJP (JJ calm) (, ,) (JJ stable)) (NNS conditions)) (PP (IN with) (NP (ADJP (ADJP (ADVP (RB no) (RB up)) (JJ draughts)) (CC and) (ADJP (RB generally) (JJ light))) (NNS winds))))) (. .)))
Whereas gliders need thermals to stay aloft, balloons need calm, stable conditions with no up draughts and generally light winds.
(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)))))) (. .)))