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THE WILSON JOURNAL OF ORNITHOLOGY • Vol 124. No. 3. September 2012 
(A) 
i Black Vulture □ Snail Kite □ Mississippi Kite 
0900 
1000 
1100 
1200 
1300 
1400 
Time of day 
RnMv h 1 percentage of Black Vultures. Snail Kites, and Mississippi Kites counted at Concepcion Watch Site, 
milrtrnn .h^ Apr ’' ' B ' Pallern of Black Vulture, Snail Kite. andMississippi Kite 
Mar 6 Apn * ° f observcd/hr >Concepcion Watch Site. Bolivia dunng austral autumn 2009 (10 
which peaked during the last week of March with 
only a few passing in early April. 
Raptors were observed flying mostly in two 
directions in migration. 47% (n = 3,300) of 
individuals migrated on the south-to-north axis. 
43% (n = 3.010) on the southcast-to-northwest 
axis with only a small fraction 10% (n 699) 
Hying in other directions. Count days exceeded 
500 raptors on 14. IX. and 29 March; the counts 
were 665, 1,527, and 2.575 raptors, respectively. 
Migration Timing .—Black Vulture (// = 747 ) 
migration exhibited two peaks in passage one 
between 14 and IS March when 47% of migrants 
(» - 349) were observed, and another between 29 
March and 4 April when 31% (n = 232) were 
observed (Fig. 1 A). Most Black Vultures (56%. 
n = 418) migrated past between 0900 and 1200 
hrs (Fig. IB). 
Flic Snail Kite (// = 396) migration peaked 
between 15 and 25 March when 92% (n = 364 1 of 
the individuals were counted (Fig. I A). Most 
Snail Kites (90%, n — 356) migrated past between 
0900 and 1200 hrs (Fig. IB)/ 
The Mississippi Kite (n = 5.571) migration 
exhibited two peaks in passage rate, one on IS 
March when 23% of migrants (n = 1.296) were 
observed, and another on 29 March when 45% (n 
= 2,507) were observed (Fig. I A). Mississippi 
