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Table 1.

Characteristics of 49 common swift trackings

MeanMinimumMaximumS.D.
Duration of tracking (s) 1366 560 3580 696 
Distance relative to the ground (m) 5012 1513 11 252 2118 
Distance relative to the air (m) 11 793 4728 42 800 7224 
IS relative to the ground ISg 0.771 0.165 0.991 0.205 
IS relative to the air ISa 0.938 0.314 0.997 0.127 
Mean flight altitude (m) 1696 918 2838 429 
Ground speed, Vg (ms-14.3 1.2 9.6 2.1 
Air speed, Va (ms-18.7 5.6 13.3 1.5 
Wind speed, Vw (ms-17.1 1.3 14.8 2.9 
Climbing speed, Vz (ms-1-0.02 -0.64 1.08 0.32 
Mean vector direction, H-W (degrees) -0.5    
 r=0.88    
Mean vector direction, T-W (degrees) -44.5    
 r=0.14    
MeanMinimumMaximumS.D.
Duration of tracking (s) 1366 560 3580 696 
Distance relative to the ground (m) 5012 1513 11 252 2118 
Distance relative to the air (m) 11 793 4728 42 800 7224 
IS relative to the ground ISg 0.771 0.165 0.991 0.205 
IS relative to the air ISa 0.938 0.314 0.997 0.127 
Mean flight altitude (m) 1696 918 2838 429 
Ground speed, Vg (ms-14.3 1.2 9.6 2.1 
Air speed, Va (ms-18.7 5.6 13.3 1.5 
Wind speed, Vw (ms-17.1 1.3 14.8 2.9 
Climbing speed, Vz (ms-1-0.02 -0.64 1.08 0.32 
Mean vector direction, H-W (degrees) -0.5    
 r=0.88    
Mean vector direction, T-W (degrees) -44.5    
 r=0.14    

The duration of trackings is from the moment when we locked the radar onto the target until we stopped tracking or lost the target.

The cumulative distances are the sum of the distances travelled in each 10 s interval.

The index of straightness IS was calculated as the resultant distance(the straight line travelled from the start to the end of tracking) divided by the cumulative distance.

r, mean vector length (Batschelet,1981) for the mean heading direction relative to the wind(H-W) and mean track direction relative to the wind (T-W)for the 49 trackings analysed.

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