Figure 5.

Mean (±SE) testis volume of male house sparrows (n = 9–10) subjected for 17 weeks to photoperiods with increasing lengths of daily light periods. a: 2L:22D, 6L:18D and 10L:14D. A slow and small testicular response occurred in 2L and 10L, but not in 6L photoperiod, except that 2 of 7 birds in this group showed small initiation at the end of the experiment. b: 14L:10D, 18L:6D and 22L:2D. A faster induction of testicular growth occurred in 22L, but regression was almost the same in all three photoperiods. Asterisk shows significant difference between 22L and 18L or 14L groups.