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THE WILSON JOURNAL OF ORNITHOLOGY • Vol 124. No. 4. December 2012 
nI ABLE : Means ' - of measur ements of activities obtained while two nestlings of the Grcy-bellied Hawk wer 
present m the nest an southern BrazH. Means were obtained from each continuous observation sesin (c^I^ 
Post-hatching 
Nestling development 
Female's time 
in the nest 
brooding (min) 
Female's time 
perched in die Parana 
pine nest tree (min) 
Number of prey 
brought to the 
ncst/pcruxl In = 22) 
Tim: (Kilsy 
thenedicgT 
by frock (ram 
~5 days 
~12 days 
Overall beige in coloration 
Nestlings became whitish 
with both bill and eyes 
355.5 ± 3.09 
163.7 ± 137.5 
16 ± 14.5 
12.3 ± 16.7 
0.66 ± 0.81 
0.50 ± 0.70 
20 ± 105 
30.5 z 3.33 
—20 days 
—25 days 
clearly black, and legs yellow 
Thc flight feathers became grayish 
The upper parts of the wings 
became predominantly black. 
141 ± 69.7 
174 ± III 
0.60 ± 0.58 
1 ± 0.00 
46.7 ± 1.90 
38 ± 16.3 
the first black streaks appeared 
on their flanks and the first 
black band also appeared in 
the tail; the first flecking on 
the wings was observed 
~35 days The top of the head became black with 
increased streaking in the flanks 
~40 days The pattern of black streaks on the 
underparts was almost complete, 
and the cheeks, neck, and sides 
129 ± 86.9 1.25 ± 0.96 28 ± 10.7 
04 ± 05.3 1.25 ± 0.00 13 ±04.5 
of the breast begin to turn 
rufous (Fig. 1C) 
Ruddy Ground Dove (Columbine talpacoti) < 
one occasion during one of her aggressive attaci 
in response to human presence during || 
incubation period. 
Time spent by the female in the nest decrease 
as the nestlings matured (Table 1), although sh 
usually remained next to the nest perched on 
branch (5-30 m distant). The time spent feedin 
the nestlings appeared similar throughout thei 
development (Table 1). We did not observe tl„ 
male directly feeding the young; his function wa 
as a hunter. He rarely visited the nest, and ther 
only lor a tew minutes, usually in the absence oi 
the female. 
Vocalizations .—The male, upon arriving in the 
nest area with prey, emitted a call composed of 
single notes (Fig. 3A) to alert the female which 
responded with a similar call, also composed of 
calls (Rr'3B) Ut Th h,Ch r T* IODger than thc male 
calls (Ftg 3B). Thus, both would be found in the 
mid-level of the forest in the air emitting 
distinctive, high-pitched calls (Fig. 3 C )- the 
female would then fly 50-100 « from the nest 
with the prey and continue calling (varying 
between 3 and II times/min). The female was 
observed on some occasions emitting this call 
when perched on a branch next to the nest in the 
absence ol the male, possibly seeking delivery of 
food. 
We identified two other Grey-bellied Hawk 
vocalizations during the reproduction period: an 
alarm call performed by adults and a food- 
beggtng call performed by the fledgling. The 
alarm call was relatively long (almost 3 sec), 
composed of seven to eight melodic notes 
repeated in a rapid rhythm, and was given by 
t e adults in response to intruders or potential 
{! re a,ors -*D). The food-begging call of the 
ctgling was given when receiving or seeking 
°° ^8- 3E). The tood-begging call had varia- 
ttons ased on the proximity of food; motivation 
seemed higher when the male was arriving and 
cn tng in the nest area and. alternatively, 
motivation was lower when the fledgling was 
seeking food. 
Appearance oj Adults .—The female had a pure 
w ute breast and neck with two dark stripes on the 
n . ec ’ l " ,er hack was dark gray, as were also the 
c ee s, having an almost black appearance. This 
coloration extended until the top of the head 
creating a 'helmet' effect. The area around the 
eyes up almost to the bill was yellow. The male 
was 30-40% smaller than the female. He also 
had a while breast and neck, but his back and 
