the five previous observations were plotted against the corresponding observation time, and the curve extrapolated to where it intercepted the score of 240. This point was assigned a value of zero to represent the best estimate of the complete regrowth of the 48 indicator feathers or a score of 240. Scores obtained at each measurement for each bird were then plotted beginning at zero and continuing back to the beginning of molt. Thus, days to completion of molt is plotted against the corresponding molt score. Since the times for each observation were different, the scores at 10 day intervals were obtained for each bird and the curves plotted. The time required for each bird to achieve the last half of its molt was also determined. Controls The individual curves for regrowth of flight feathers on five unexposed (control) birds are shown in Fig. 2. It can be seen that the shape of the molt curve for flight feathers is sigmoid and that molting requires approximately 115 to 150 days. From each of the curves plotted in Fig. 2, the time required for each bird to achieve the last half of its molt (score of 120 to 240) was noted and the mean ± standard deviation, 59.6 ± 5.8 days, computed.
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