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THE WILSON JOURNAL OF ORNITHOLOGY • Vo/. 124, No. 3. September 2012 
2 4 6 8 10 12 14 16 18 
Nestlings age (days) 
FIG. 4. Mean ± SD body mass of Red-bellied Grackle nestlings during development at the nest (« = 1 1 . from 4 nests), 
the gray line shows the logistie growth curve (R 2 = 0.98) based on the equation W(r) = A/(l + e 
observation time tor the three nests monitored 
from egg laying to hatching (37 hrs). The indi¬ 
vidual incubating the eggs was a female, which 
was fed an average of 1.9 ± 1.1 times/hr (n = 3 
nests) by other members of the group during 41 hrs 
of observations (data from 12 of the 14 days of 
the incubation period). The incubating duties on 
the nest were alternated between females (/? = 3 
events), and were followed by a provisioning 
event. We directly observed all eggs hatch at two 
nests, both with a clutch si/e of four eggs and. in 
all cases, the entire clutch hatched within 24 hrs. 
Adult males did not participate in brooding but 
remained perched in the surrounding trees, often 
vocalizing. 
Nestlings. The nestling period was 17.3 ± 
1.3 days (n = 5). Nestlings weighed 5.2 ± 0.7 g (/; 
= 5, from 2 nests) at hatching. Nestlings had light 
orange skin, black downy feathers, while claws, a 
whitish bill with a darker lip. and a bright yellow 
gape (Fig. 2). Nestling growth rate (AT was 0.304 
0? = 11 from 4 nests; Fig. 4). These 12 nestlings 
opened their eyes on the sixth or seventh day. The 
eyes were dark brown, and the bill was black at this 
point. Nestlings were covered hy a dull black 
plumage by day 15 except in the naked area around 
the eyes, and on the lower breast and belly where 
the feathers were reddish orange. Nestlings were 
active at that age and able to exercise their wings 
and perch by themselves. Nestlings fledged when 
16 to 18 days ot age with a mean mass of 76.3 ± 
10.1 g (n - 4 from 2 nests), Their flight ability was 
limited, the tail was <50% of full length, and flight 
feathers were still growing. Fledglings continued to 
be led by members of the group. 
Eight fledglings were still fed by the group 
2 weeks after leaving nests, their tails were sail 
growing, and their overall plumage was brownish 
black with orange or dull red bellies. Ten fledg¬ 
lings —6 wrecks of age u'ere able to forage more nr 
less independently along with the group and were 
clearly distinguishable from older birds. Six 
juveniles still had dull plumages after 12 months 
but they had dark-yellow irides. were similar in 
size to subadults and females, and started to 
participate as helpers in the group (observations 
from 4 breeding groups). Individuals (n = 4) at 
22 months of age, and probably after completing a 
second molt, had bicolored irides and reached the 
plumage brightness and coloration of adults, and 
continued to serve as helpers in their group. 
The brooding adult remained the first 5 days of 
the nestling period at the nest (n = 3: Fig. 5) ano 
was ted by helpers, during which time the 
provisioning rate of the nestlings averaged I5-S 
visits/hr (55 hrs of observation: Fig. 5). Sonic 
food was delivered by regurgitation (n = 4 - 
groups) but, after the fifth day, it was progres¬ 
sively passed from helpers to nestlings as parts 
whole items. Helpers occasionally passed looti 
items to the brooding individual at the nest that n 
turn delivered food to nestlings. Provisioning 
young decreased gradually within the last 
days of the nestling period (Fig. 5). We identified 
450 prey items during 95 hrs of observations at 
three nests. The nestlings’ diet consisted mainly o( 
arthropods (72%. n = 353), fruits and flower parts 
of melastome (Tibouchina lepidota, 9.4%. ” 
44). and small vertebrates (3 unidentified frogs- 
and 4 An olis maria rum lizards). Provisioning 
