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Table of Contents
Great Circle Hypotheis
Magnetoclinic Hypothesis
Magnetic-Latitude Hypothesis
Compass Bearings Hypothesis
Suns' Azimuth Hypothesis
Expansion-Contraction Hypothesis
Always Advance Hypothesis
Never Go Back Hypothesis
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Analysis of Field Data for the 1987 Monarch
Butterfly Migration in Calhoun, Georgia
 Table I f
Descriptive statistics of the September
28, 1987 Observations of the Danaus plexippus migration in Calhoun, Georgia |
Statistic |
Value |
Comments |
1)
Sample size |
26 |
Observations 3, 15, 28
of D. plexippus* and 6 of other butterflies were not included in the
analysis. |
2) Sum of
sines |
-24.70196 |
Divide by sample size to get mean sine (line 4). Also
needed when pooling data from other studies. |
3) Sum of
cosines |
+2.67929 |
Divide by sample size to get mean cosine (line 5).
Also needed when pooling data from other studies. |
4) Mean sine |
-0.95008 |
Values for lines 4 and 5 are used with
sample size (line 1) to calculate length of the mean vector (line 6). |
5) Mean cosine |
+0.10305 |
6)
Length of mean vector |
0.95565 |
An index of dispersal of
bearings. Used to determine values for lines 9 and 13. |
7) Sine of
mean vector |
-0.99417 |
Values for lines 7 and 8 are obtained by
dividing the values from lines 4 and 5 by the value for line 6. The resulting
sine and cosine are used with a Trigonometry Table of sines and cosines to
extrapolate the angle of the mean vector, in this case the Magnetic mean bearing (line10
). |
8) Cosine of
mean vector |
+0.10783 |
9) Angular
deviation |
±16.2° |
This value is determined from Tables that convert mean
vector length (line 6) into angular deviation (or circular standard deviation). |
10)
Magnetic mean bearing |
276° ±16.2°
(West) |
Descriptive statistic of the
Magnetic mean bearing and the dispersion around the mean for the sample. |
11) Magnetic declination
|
-2ºW |
Subtract magnetic declination (variation) to obtain True
bearing |
12) True
mean bearing |
274° ±16.2°
(West) |
Descriptive statistic of the True mean
bearing and the dispersion around the mean for the sample. |
13) 95%
confidence intervals |
±6° |
Values from lines 1 and 6 are used
to extrapolate 95% (or 99%) Confidence Intervals (C.I.) from appropriate Tables. |
* No numerical data was recorded for vanishing bearing.
The 6 observations of other butterflies were # 8, 26, 31, 32, 34, and 35.
Comments
Wind was SE for most of day.
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