( ( Because ( birds ( generally ( lack ( some ( of ( our ( worst ( human traits ) ) ) ) ) ) ) ) ) ( , ( I ( ( believe ( they ( ( were there ) ( to ( ( ( lift up ) ( ( the spirits ) ( of ( their friends ) ) ) ) ( in bondage ) ) ) ) ) ) . ) ) ) )
(ROOT (S (SBAR (IN Because) (S (NP (NNS birds)) (ADVP (RB generally)) (VP (VBP lack) (NP (NP (DT some)) (PP (IN of) (NP (PRP$ our) (JJS worst) (JJ human) (NNS traits))))))) (, ,) (NP (PRP I)) (VP (VBP believe) (SBAR (S (NP (PRP they)) (VP (VBD were) (ADVP (RB there)) (S (VP (TO to) (VP (VB lift) (PRT (RP up)) (NP (NP (DT the) (NNS spirits)) (PP (IN of) (NP (PRP$ their) (NNS friends)))) (PP (IN in) (NP (NN bondage)))))))))) (. .)))
Because birds generally lack some of our worst human traits, I believe they were there to lift up the spirits of their friends in bondage.
(ROOT (S (NP (JJ Adult) (NNS humans)) (VP (VBP lack) (NP (NP (DT some)) (PP (IN of) (NP (NP (DT the) (VBG defining) (NNS traits)) (PP (IN of) (NP (NNS chordates))))))) (. .)))