Tactics and Vectors 98/99
                           

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Great Circle Hypotheis  

Magnetoclinic Hypothesis

Magnetic-Latitude Hypothesis

Compass Bearings Hypothesis

Suns' Azimuth Hypothesis

Expansion-Contraction Hypothesis

Always Advance Hypothesis

Never Go Back Hypothesis

 

 

Analysis of Field Data for the 1988 Monarch Butterfly Migration in Rasaca and Calhoun, Georgia

left arrowarrow leftTable XII a
Mean Vanishing Bearing for Danaus plexippus in Northwest Winds

Descriptive statistics for the September 26 to October 2, 1988, observations in Resaca and Calhoun, Georgia

Statistic  

Value

Comments

1)       Sample size     

8

 Records with non-numercical records for vanishing bearing or  wind (e.g. N instead of 360°) were not included in the analysis. 

2)       Sum of sines        

-3.30035

 Divide by sample size to get mean sine (line 4).  Also needed when pooling data from other studies.

3)       Sum of cosines

-6.63628

 Divide by sample size to get mean cosine (line 5).  Also needed when pooling data from other studies.

4)       Mean sine

-0.41254

 Values for  lines 4 and 5 are used with sample size (line 1) to calculate length of mean vector (line 6).

5)       Mean cosine

-0.79535

6)       Length of mean vector  

0.89597

 An index of  dispersal of  bearings.    Used to determine values for lines 9 and 13. 

7)       Sine of mean vector      

-0.46404

 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  

-0.88769

9)       Angular deviation         

±25.6°

 Determined from Tables that convert mean vector length (line 6) into angular deviation (or circular standard deviation).

10)     Magnetic mean bearing

208°±25.6°

 Descriptive statistic for the True mean bearing and the dispersion around the mean for the sample. 

11)     Magnetic declination     

-2°W

 Subtract magnetic declination (variation) to obtain True bearing

12)     True mean bearing          

206°±25.6°

 Descriptive statistic for the True mean bearing and the dispersion around the mean for the sample.  

13)     95% confidence intervals

±26°

 95% Confidence Intervals (C.I.) are extrapolated from a chart using values from lines 1 and 6.

Comments: