Ocampo el al • BREEDING BIOLOGY OF HYPOPYRRHUS 
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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 
Time (days) 
FIG. 5. Nest attentiveness of helpers during the nestling period of the Red-bellied Crackle depicted as the hourly 
provisioning frequency to nestlings (gray) and to brooding frequency (black i. Data are from two breeding events. 
mostly by immature helpers and females (94%) 
and less by adult males (6%). based on 627 visits 
at three nests. 
Fledgling Survival. —The daily survival rate 
was 0.97 and nesting success was 0.39 in = 24 
nests), hatching success was 92%, and 86% of 
'hesc nests were depredated during the nestling 
period. The cumulative fledgling survival over 
tour breeding seasons (2006-2009) was 29%. 
corresponding to 19 fledglings (from X nests) from 
^ eggs laid (21 total nests) that ultimately 
integrated into their family groups. Nests were 
also lost to harsh environmental events such as 
heavy rainstorms or to unknown factors. All 
groups that lost their nest reinitiated breeding 
during the same season, and there were three 
double-brooding events in 2010 (unpubl. data). 
DISCUSSION 
Red-bellied Graekles exhibited a cooperative 
breeding system with juveniles staying in natal 
territories and assisting with subsequent breeding 
df °rts of their family group. Nest construction, 
brooding, and nestling care was mostly by females 
and young helpers, while adult males remained in 
'he territory often vocalizing, which we interpret 
as involved in social cohesion and defense. 
Cooperative breeding at Alto San Miguel is 
consistent with previous casual encounters with 
nesting groups of Red-bellied Crackles not only at 
this study site, but elsewhere across its disjunct, 
restricted range where nests were also attended by 
three or more individuals (Ochoa and Cuervo 
1998, Cuervo 2002; J. J. Leon and S. Vargas 
Troncoso, pers. comm,). We demonstrated by 
color-banding juveniles, that they become helpers 
at the nest (Skuteh 1935) of their own family 
group in subsequent years. However, behavioral 
and genetic studies are needed to understand 
juvenile dispersal and kin structure in this 
population. Family groups in the disturbed 
landscape of Alto San Miguel were cohesive 
throughout the year, but this may not be the case 
in populations from less disturbed habitats where 
large flocks arc observed outside the breeding 
season (AMC. pers. obs.). Unknown social 
interactions and the ecological conditions ot 
undisturbed habitats could be involved in fusion 
and division of groups during non-breeding and 
breeding seasons, respectively. 
The breeding activity of Red-bellied Graekles 
in our study area was concentrated between 
March and June, which agrees with previous 
anecdotal information of breeding in this species 
(Hilty and Brown 1986. Ochoa and Cuervo 1998. 
Jaramillo and Burke 1999), We did not detect any 
indication of breeding during four visits to the 
same transect from August to December. 
The nests and eggs of the Red-bellied Gracklc 
described here match the illustrations and 
