( ( As ( a result ) ) ( , ( ( ( the ( only extinctions ) ) ( that ( I ( am confident ) ) ) ) ( ( ( ( had ( nothing ( to ( do ( with ( human activity ) ) ) ) ) ) , ) ( ( at least ) ( among ( ( birds , ) ( ( the group ) ( ( with which ) ( I ( am ( ( ( most familiar ) , ) ( were ( species ( that ( disappeared ( as ( ( the results ) ( of ( natural disasters ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) . ) ) ) )
(ROOT (S (PP (IN As) (NP (DT a) (NN result))) (, ,) (NP (NP (DT the) (JJ only) (NNS extinctions)) (SBAR (IN that) (S (NP (PRP I)) (VP (VBP am) (ADJP (JJ confident)))))) (VP (VBD had) (NP (NN nothing) (S (VP (TO to) (VP (VB do) (PP (IN with) (NP (JJ human) (NN activity))))))) (, ,) (PP (ADVP (IN at) (JJS least)) (IN among) (NP (NP (NNS birds)) (, ,) (NP (NP (DT the) (NN group)) (SBAR (WHPP (IN with) (WHNP (WDT which))) (S (NP (PRP I)) (VP (VBP am) (ADJP (ADJP (RBS most) (JJ familiar)) (, ,) (SBAR (S (VP (VBD were) (NP (NP (NNS species)) (SBAR (WHNP (WDT that)) (S (VP (VBD disappeared) (PP (IN as) (NP (NP (DT the) (NNS results)) (PP (IN of) (NP (JJ natural) (NNS disasters)))))))))))))))))))) (. .)))
As a result, the only extinctions that I am confident had nothing to do with human activity, at least among birds, the group with which I am most familiar, were species that disappeared as the results of natural disasters.
(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))))))))))) (. .)))