. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 100 WILLIAM L. ENGELS -15 Dates by which beak became black A- None (2) F- Feb. 12,19, Mar. 19 G - Dec. 7, Feb. 19 H- Jan. 29, Feb. 2,12 a o IT LLl a. o 36° N -13 -12. AUG 1 SEPTEMBER 1 OCTOBER NOVEMBER DEC FIGURE 4. Experiments to determine length of photoperiod, and duration of treatment, which may release bobolinks from photorefractoriness during October and November. On October 2 ten birds were removed, from the natural day-lengths (including civil twilight) of Lat. 36° N., to constant daily photoperiods of different leng
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 100 WILLIAM L. ENGELS -15 Dates by which beak became black A- None (2) F- Feb. 12,19, Mar. 19 G - Dec. 7, Feb. 19 H- Jan. 29, Feb. 2,12 a o IT LLl a. o 36° N -13 -12. AUG 1 SEPTEMBER 1 OCTOBER NOVEMBER DEC FIGURE 4. Experiments to determine length of photoperiod, and duration of treatment, which may release bobolinks from photorefractoriness during October and November. On October 2 ten birds were removed, from the natural day-lengths (including civil twilight) of Lat. 36° N., to constant daily photoperiods of different lengths, in four groups. Development of black pigment in the beak indicates testicular recrudescence. The dotted line is a rough approximation of day-length experienced by an "average" bobolink during southward, post-nuptial migration (cf. Figure 3). Group F These three birds were exposed to 12f-hour photoperiods (light intensity about 90 foot-candles) for six weeks; on November 13 the photoperiod was increased to 14 hours. Two birds developed beak pigmentation in early and mid-February, the last in the third week of March. Group G As in the previous group the initial photoperiods were 12J hours (light intensity 90 foot-candles), but these were continued for only five weeks; the 14-hour photo- periods were begun on November 6. One bird developed beak pigmentation sur- prisingly early, during the first week of December, another not until the third week of February. The third bird accidentally hung itself in the cage during the period December 22-26. At the time the accident was discovered the lower beak was discolored, but the testes were minute. Group H The initial photoperiods were 12^ hours (light intensity about 45 foot-candles) and they were continued for only four weeks. On October 30 the photoperiods were increased to 14 hours. One bird developed beak pigmentation during the last week in January, the other two in early February. General conclusion The post-nuptial
Size: 1836px × 1361px
Photo credit: © Library Book Collection / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
