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THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 124. No. 3. September 2012 
The Wilson Journal of Ornithology 124(3):636-640. 2012 
Raptor Migration at Concepcion, Bolivia 
Matias A. Juhant 1 - 2 
ABSTRACT.—I conducted the second austral au¬ 
tumn raptor count at Concepcion Watch Site in the 
eastern Bolivian lowlands to document species compo¬ 
sition. liming, and abundance of migrating raptors 
between 10 Match and 6 April 2009. I counted migrants 
for 26 days (134.5 Ill's) recording 6,979 migrating 
raptors of 16 species. Mississippi Kites Uctinia tnissis- 
sippienm) comprised 80% (n 5.571). Black Vultures 
1 1% (Cnragyps atrottiy n 747). and Snail Kites 5% 
(Rostrhatuus sociahi/is , n - 396). The remaining 4% 
(n = 263) included 13 species and other unidentified 
raptors, I also recorded lion-raptor species on migration 
from the lookout, including 36 Maguari Storks (Cieonia 
maguuri), a flock of I I Anhinga (Anhinga anhinga), 
and thousands u! Barn Swallows (77 irunda rustica). My 
observations confirm previous records suggesting a 
significant raptor migration occurs at the Concepcion 
Watch Site in the austral autumn. Raptor monitoring 
should continue at Concepcion annually and the site 
used to promote raptor conservation and awareness in 
Bolivia. Received 12 December 2011. Accepted 10 
April 2012. 
Raptor migration in South America is largely 
undescribed with lew published papers using 
standardized migration monitoring protocols. This 
topic is understudied, but of international concern 
(Juhant 2011). Thirty-five raptor migration watch 
sites have been recognized in South America of 
which eight are in Bolivia (Juhant 2011). Con¬ 
cepcion Watch Site in the eastern Bolivia low¬ 
lands was previously identified for conducting 
long-term studies of raptor migration in both 
austral spring and autumn (Davis 1989; Zalles and 
Bildstein 2000; Olivo 2001, 2005. 2007a. b). 
The first studies of raptor migration at Con¬ 
cepcion Watch Site began in the mid 1980s when 
several thousand Mississippi and Plumbeous kites 
(Ictinia tnississippiemis. I. phtmbea ) were count¬ 
ed in two consecutive austral springs (Davis 
1989). Olivo (2001) conducted the first systematic 
raptor migration count at Concepcion Watch Site 
in 2000 counting >40.000 raptors during late 
Faculty of Natural Sciences and Mathematics, Univer¬ 
sity of Maribor. Slovenia. 
2 Current address Guriceljska 16 LjuMjana-Seiitvid 1000 . 
Slovenia; e-mail: maliasJuhantePyaJuio.com.ur 
October. These included >37.000 Mississippi 
Kites (Olivo 2001). Subsequent austral spring 
counts in 2001 and 2003 recorded >120,000 and 
>150.000 raptors, respectively, between late- 
September and late-November (Olivo 2005. 
2007a. b). The Mississippi Kite was the most 
common species in both seasons with >115.000 
and >145.000 kites recorded (Olivo 201)4. 
2007b). The first and only study of raptor migra¬ 
tion during austral autumn was conducted in 
March 2003 and recorded 5.000 raptors (Olivo 
2007a, b). These included —4.000 Mississippi 
Kites (Olivo 2007b). These studies reveal a large 
number ol soaring raptors have been recorded at 
Concepcion, but migration patterns at the site are 
not well understood (Olivo 2004). 
I documented species composition, timing, and 
abundance of migrating raptors at Concepcion 
Watch Site, Bolivia during austral autumn 2009 
using standardized migration monitoring techniques. 
METHODS 
Study Area .—Concepcion town (16 08' S. 
62 02' W). Nuflo de Chavez Province. Santa Cruz 
Department. Bolivia is 270 km (by road) northeast 
ol Santa Cruz de la Sierra. Concepcion Watch Site 
is 2 km southwest of the town center in the gated 
community. Guantdtiatno. The lookout is on a pier 
at the loot of Sapocd Lake created by a dam and 
has a view of 360 degrees. Floristically. the 
vegetation of the area contains elements of 
evergreen tropical rainforest of the Amazon Basin 
and subtropical thorn-scrub of the Gran Chaco 
(Davis 1993). The region has dry (May-Ocl) and 
wet seasons (Nov-Apr) with rainfall exceeding 
1,100 mm, and an average temperature of 24.5 C 
(Davis 1993). 
Sampling .—I counted migrating raptors at the 
Concepcion Watch Site during austral autumn 
2009. The count was conducted over 26 days 
1134.5 hrs) in March and April: 21 days in March 
(10-12. 14-31; 113 hrs) and 5 days in April (2-6; 
21.5 hrs). I counted 6 hrs per day (0900-1500 
lies). The count was during the wet season, and 
66% (88 hrs) of the count days were overcast. 
26%' (35 hrs) were sunny, and 8% (11.5 hrs) were 
