Boesinget al. • REPRODUCTION OF THE GREY-BELLIED HAWK 
773 
horizontal branches radiating from the trunk at the 
same height, providing a stable foundation for 
nests (Seipke and Cabanne 2008). 
The Grey-bellied Hawk nest seems no different 
from those of other neotropical Accipiter (e.g.. 
Bicolored Hawk. Bierregaard 1994; Rufous- 
thighed Hawk, Seipke and Cabanne 2008). Clutch 
size is variable among species of Accipiter ; the 
Bicolored Hawk varied between one and four 
eggs, while the Sharp-shinned Hawk has 2-3 in 
the Caribbean. 3-5 in Mexico, and 4-5 in North 
America (Ferguson-Lees and Christie 2001). 
Nestlings of the Grey-bellied Hawk appear to 
remain longer in the nest (— 49 days) than nestlings 
of Bicolored Hawks (~ 35 days, Throstrom and 
Quixchan 2000). 
Thiollay (1994) reported fledglings are depen¬ 
dent on food brought by adults for at least several 
days after leaving the nest. The fledgling Grey- 
bellied Hawk left the nest and continued to 
receive prey from the male for at least 60 days, 
and possibly longer. Bicolored Hawk fledglings 
similarly remain close to the nest and are 
dependent on their parents for nearly 2 months 
or more (Ferguson-Lees and Christie 2001). 
The role of the male as hunter and the female as 
feeder (Thiollay 1994) was observed for the Grey- 
bellied Hawks we studied, similar to the majority 
of Accipiter species. We did not observe the 
female Grey-bellied Hawk bringing food for 
nestlings while they were growing, as has been 
described generally for Accipiter (Thiollay 1994). 
It seems the Grey-bellied Hawk is a bird-hunter, as 
suggested by Bierregaard (1994) and by associa¬ 
tion with its neotropical congeners (e.g.. Bicolored 
Hawk. Throstrom and Quixchan 2000; Chilean 
Hawk \A. chilensis], Rojas et al. 2004: White¬ 
breasted Hawk. Jenner 2010). Our observations (8 
of 9 prey were birds) and the time of the day the 
male Grey-bellied Hawk hunts, coincided with 
higher activity of birds. 
This was the second year the Grey-bellied 
Hawk pair was known to have used the same 
location to raise their young, and it is possible the 
same nest was used, because the female defended 
the same nest area in the presence of humans in 
the previous year. We suspect this might be the 
third year the site was used by this pair, because in 
mid-September 2010. in addition to the pair of 
Grey-bellied Hawks, we also observed one 
.juvenile in the nest area. Many Accipitridae 
species re-use old nests, to which they add new 
material (Thiollay 1994). Gundlach’s Hawk (A. 
guiullachi), a species endemic to Cuba, appears to 
use the same nest for at least 3 years or more 
(Bierregaard 1994). Whether or not a nest-site is 
changed from I year to another is strongly related 
to breeding success in the previous year (Thiollay 
1994). 
Our observations do not enable us to resolve if 
the nest found by Vries and Melo (2001) belonged 
to the Slaty-backed Forest Falcon or Grey-bellied 
Hawk, as suggested by Thorstrom (2002). Mor¬ 
phological features reported by Vries and Melo 
(2001) are general and a more precise description 
is needed to reach a conclusion on species 
identity; however, some ecological features re¬ 
ported by those authors are not consistent with our 
observations for the Grey-bellied Hawk. 
Our Field observations confirm the secretive 
behavior attributed to the Grey-bellied Hawk 
(Santos et al. 2009). This secretive behavior 
would explain the rarity of records and why it is 
easily overlooked. It became difficult to find the 
adult pair or the fledgling in the nest area soon 
after the fledgling had left the nest, and we were 
barely able to detect the calls of the fledgling 
seeking food. This species seems to be naturally 
rare and its shy behavior contributes to its low 
detection. 
ACKNOWLEDGMENTS 
We thank the Boesing Family lor assistance throughout 
the entire field period with logistical and total support; the 
farm supervisor Ladislau Cubas Jr. who gave permission to 
access the area where the field work was performed; Artur 
Battisti F'ilho who provided the photographic equipment 
used during the field work, and Tiago Zaiden who helped 
with improvement of the spectrograms. We appreciate the 
valuable suggestions by S. H. Seipke, N. .1, Collar, and C. E. 
Braun, which substantially improved die last version of this 
manuscript. The first author received a research grant from 
CAPES (Coordination for the Improvement of Higher 
Level Personnel. DS). and the third author received a 
research grant from CNPq (Brazilian Council for Develop¬ 
ment of Science and Technology. 305593/07-3). This paper 
is dedicated to the first author's mother. Mse. Cila 
Tere/inha Friedrich Boesing I In Mcnioriam ). who support¬ 
ed all of her field work. 
LITERATURE CITED 
Bierregaard. R. O. 1994. Grey-hellied Goshawk. Page 45 
in Handbook of birds of the World. Volume 2. New 
World vultures to guineafowl (J. del Hoyo, A. Elliott, 
and J. Sargatal. Editors). Lynx Editions, Barcelona, 
Spain. 
Bioacoustics Research Program. 2011. Raven Pro: 
interactive sound analysis software (Version 1.4). 
