( ( ( About one-quarter ) ( of ( all ( bird species ) ) ) ) ( ( are ( extinct ( as ( ( a result ) ( of ( human actions ) ) ) ) ) ) . ) )
(ROOT (S (NP (NP (RB About) (NN one-quarter)) (PP (IN of) (NP (DT all) (NN bird) (NN species)))) (VP (VBP are) (ADJP (JJ extinct) (PP (IN as) (NP (NP (DT a) (NN result)) (PP (IN of) (NP (JJ human) (NNS actions))))))) (. .)))
About one-quarter of all bird species are extinct as a result of human actions.
(ROOT (S (NP (NNP Human) (NNS actions)) (VP (VBZ is) (ADJP (JJ responsible) (PP (IN for) (NP (NP (DT the) (NN extinction)) (PP (IN of) (NP (NP (NNS hundreds)) (PP (IN of) (NP (NP (NNS species)) (PP (IN of) (NP (NNS birds))))))))))) (. .)))