DIFFERENTIAL MIGRATION OF SEX- AND AGE-CLASSES AS SHOWN BY THE TOPEKA SAMPLE.--Smaller samples have not been treated. Species affording samples seemingly large enough to justify at least preliminary analysis were: Catbird, Red-eyed Vireo, Mourning Warbler, Dickcissel, Nashville Warbler, Orange-crowned Warbler, Yellow-throat, and Lincoln Sparrow (Fig. 1). For all of these except the Catbird and Dickcissel, at least two samples from a week or more apart were available for comparison in an effort to detect trends in migration. Fig. 1 shows the actual ratios of sex- and age-classes observed in samples of the species listed above. Each of the last four species provided two separate samples, of sufficient size to warrant an attempt at measuring the statistical significance of the observed changes in adult-immature ratios (Table 2). TABLE 2.--STATISTICS OF THE RATIOS OF ADULTS TO IMMATURES IN FOUR SPECIES ======================================================================= Species | Dates |Total | Number | Differ- |P[3] | of samples |number| and | ence | | | |percentage |(in %)[2]| | | |of adults[1]| | --------------|--------------------|------|------------|---------|---- Nashville |Oct. 1 (93) | 156 | 45 (.484) | .071 |.36 Warbler |Oct. 5-7 (63) | | 26 (.413) | | | | | | | Orange-crowned|Sept. 25-Oct. 1 (19)| 44 | 3 (.158) | .282 |.05 Warbler |Oct. 5-9 (25) | | 11 (.440) | | | | | | | Yellow-throat |Oct. 1 (115) | 159 | 62 (.540) | .085 |.34 |Oct. 5-8 (44) | | 20 (.455) | | | | | | | Lincoln |Oct. 1-3 (44) | 71 | 27 (.614) | .318 |.01 Sparrow |Oct. 6-10 (27) | | 8 (.296) | | ---------------------------------------------------------------------- Footnotes: [1] Percentage of immatures equals 1.000 minus percentage of adults. [2] Standard error of the difference between ratios was computed by the formula [Greek: s]^e = sqrt(P_e Q_e (1/N_1 + 1/N_2)) where P_e equals percentage of adults and Q_e equals percentage of immatures in the entire sample. [3] Probability of error; _i. e._, a P of .01 means there is one chance in 100 that the difference observed does not represent an actual difference in nature.