( This ( ( means ( that ( ( when ( paired ( to ( a ( non ( factor mate ) ) ) ) ) ) ( they ( ( produce , ) ( in ( ( ( ( the case ) ( of ( the ( ( ( SF ,50 ) % ) ( SF birds ) ) ) ) ) and ) ( ( 50 % ) ( non ( factor birds ) ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (DT This)) (VP (VBZ means) (SBAR (IN that) (S (SBAR (WHADVP (WRB when)) (S (VP (VBN paired) (PP (TO to) (NP (DT a) (NN non) (NN factor) (NN mate)))))) (NP (PRP they)) (VP (VBP produce) (, ,) (PP (IN in) (NP (NP (NP (DT the) (NN case)) (PP (IN of) (NP (DT the) (ADJP (QP (CD SF) (CD ,50)) (NN %)) (NNP SF) (NNS birds)))) (CC and) (NP (ADJP (CD 50) (NN %)) (NN non) (NN factor) (NNS birds)))))))) (. .)))
This means that when paired to a non factor mate they produce, in the case of the SF,50% SF birds and 50% non factor birds.
(ROOT (S (NP (NNP Birds)) (VP (VB pair) (PRT (RP up)) (PP (IN with) (NP (NP (DT the) (JJ same) (NN bird)) (PP (IN in) (NP (NN mating) (NN season)))))) (. .)))
Birds pair up with the same bird in mating season.