Boesing et al • REPRODUCTION OF THE GREY-BELLIED HAWK 
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Hunting sessions observed 
FIG. 2. Time of day the male Grey-bellied Hawk hunted to feed the female and young during the nesting period in the 
mixed rainforest of southern Brazil. 
cheeks were light gray with only the wings and 
the top of the head being dark gray. Both male 
and female had three dark bands on the tail. 
DISCUSSION 
This is the first description not only of the nest 
but also of some aspects of the reproductive 
behavior of the Grey-bellied Hawk that were 
previously unknown. The Grey-bellied Hawk has 
been considered by many as an ‘aberrant' 
Accipiier with obscure relationships with the rest 
of the genus (S. H. Scipke, pers. comm.). Our 
observations of its breeding biology and ecology 
revealed it may be closer to other neotropical 
Accipiiers than has been generally assumed. 
Knowledge of this hawk is so sparse that, until a 
few years ago. the juvenile, which has a plumage 
similar to the Ornate Hawk-Eagle (Spi'cn'tns 
oniatus ), was considered to be another species 
(A pectoralis). 
Sexual dimorphism between the male and 
female was apparent with the latter being 
noticeably larger (— 40%). We believe the 
surviving fledgling was also a female as on the 
last occasion the male was observed to leave prey 
in the nest (late Dec), the juvenile was taller than 
the adult male. The juvenile 40 days post- 
hedging) also had the dark bands that occur on the 
neck of the female. Schulenberg et al. (2007) 
described an important morphological feature 
distinguishing male from female Grey-bellied 
Hawks: cheek coloration. We observed the female 
had darker gray and the male lighter gray cheeks 
and agree with Schulenberg et al. (2007). 
However, one important ieature is that the female 
had a 'helmet' linked with the rest of the plumage 
of the hack and head, forming a uniform dark gray 
plumage. The male clearly had a light gray 
•helmet' with the top of the head being dark gray. 
The reproductive behavior of the Grey-bellied 
Hawk seems not to differ from that of olher 
Accipiter species. The nest of the Grey-bellied 
Hawk was in the upper parts of a tall tree, as is 
true for most of its neotropical counterparts (e.g., 
Bicolored Hawk. Thorstrom and Quixchan 2000; 
Rufous-thighed Hawk |/\. erythronemius], Seipke 
and Cabanne 2008; White-breasted Hawk \A. 
chionogasier |. Jenner 2010). The Rufous-thighed 
Hawk has similarly been observed to build its nest 
close to the top of Parana pine (Seipke and 
Cabanne 2008). Platt (1976) reported Sharp- 
shinned Hawks (A. st rial us) also have a prefer¬ 
ence for nesting in conifers. 
Parana pine is the preferred nesting tree of the 
Rufous-thighed Hawk according to Seipke and 
Cabanne (2008). These authors suggest many 
factors could contribute to this choice and. of 
these factors, one seems more important and 
applicable to the Grey-bellied Hawk. These trees, 
other than the nest tree, usually have variable 
amounts of sticks in the upper branches, forming 
platform-like structures that could serve to 
confuse potential predators (Seipke and Cabanne 
2008). This is consistent with our field observa¬ 
tions because potential predators flying above the 
canopy were tolerated in the nest area by the 
Grey-bellied Hawk, in contrast to those flying 
through it. The Parana pine presents nearly 
