( However ( , ( ( ( ( ( ( human influences ) ( on ( certain populations ) ) ) , ) ( through ( both ( environmental ( ( alterations and ) harvests ) ) ) ) ) , ) ( ( have ( ( changed ( ( ( ( ( ( the magnitude ) , ) causes ) , ) and ) ( importance ( of ( waterfowl mortality ) ) ) ) ) ( during ( the ( breeding season ) ) ) ) ) . ) ) ) )
(ROOT (S (ADVP (RB However)) (, ,) (NP (NP (JJ human) (NNS influences)) (PP (IN on) (NP (JJ certain) (NNS populations))) (, ,) (PP (IN through) (NP (DT both) (JJ environmental) (NNS alterations) (CC and) (NNS harvests))) (, ,)) (VP (VBP have) (VP (VBN changed) (NP (NP (DT the) (NN magnitude)) (, ,) (NP (NNS causes)) (, ,) (CC and) (NP (NP (NN importance)) (PP (IN of) (NP (JJ waterfowl) (NN mortality))))) (PP (IN during) (NP (DT the) (VBG breeding) (NN season))))) (. .)))
However, human influences on certain populations, through both environmental alterations and harvests, have changed the magnitude, causes, and importance of waterfowl mortality during the breeding season.
(ROOT (S (NP (NP (DT A) (NN change)) (PP (IN of) (NP (NP (NN season)) (CC and) (NP (JJR less) (NN food))))) (ADVP (RB usually)) (VP (VB cause) (S (NP (JJ certain) (NNS animals)) (VP (TO to) (VP (VB migrate))))) (. .)))
A change of season and less food usually cause certain animals to migrate.