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THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 123. No. 2. June 2011 
the border) of the reserve. The topography is 
nearly flat at an altitude — 1.040 m asl and the area 
is covered with a mosaic of different vegetation 
physiognomies typical of the Cerrado with some 
patches of grasslands, open cerrado, shrubby 
grassland, cerrado sensu stricto , and strips of 
gallery forest (Ribeiro and Walter 1998). 
Data Collection .—We searched for nests during 
four breeding seasons from August to December 
2003-2006. We did not search for nests during 
other months, but the population was monitored 
weekly during the entire year and no evidence of 
active nests was found. We captured birds weekly 
and recorded molt, and presence of brood patches 
and cloacal protuberances as indicators of repro¬ 
duction. We used data on nesting activity, brood 
patches, and cloacal protuberances to estimate the 
length of (he breeding period. 
Active nests were checked every 3-4 days. 
Nests were checked every 2 days just prior to 
hatching and fledgling to estimate time intervals 
more precisely. We estimated timing of nest 
initiation, clutch size, and the incubation and 
nestling periods from these observations. The 
incubation period was estimated for nests found 
before eggs were laid and monitored until the first 
egg hatched. The nestling period estimation 
included nests with known dates of hatching and 
voluntary departure from the nests. 
Statistical Analysis .—Means ± standard devi¬ 
ations are presented. Differences in clutch size 
among years were verified with Williams G-test. 
We set significance at a = 0.05 and statistical 
analysis followed the BioEstat 5.0 (Ayres and 
Ayres Jr. 2000) statistical package. 
RESULTS 
Breeding Period .—The Shrike-like Tanager 
bred from late August to early December (n = 
120 nests. Fig. 1). Breeding lasted 13 weeks in 
2003, 2005, and 2006, and 11 weeks in 2004. The 
earliest evidence of breeding was in the second 
week of August 2003 when a female was seen 
gathering nest material. The first active nests 
(with eggs) were found on 29 August 2003 
(Fig. 1). The peak of breeding activity (most 
active nests) occurred in October and the last day 
of fledging was 10 December 2005. 
The earliest nest initiation varied among years. 
First nests tended to be found at the start of the 
rainy season. The start of the breeding season 
varied -30 days among the 4 years studied 
( ig. 1). Breeding season length was more or less 
constant, regardless of timing of initiation, except 
in 2004. The dry season ended late in 2004. at the 
end of September, and breeding started later, was 
of shorter duration, and ended later. 
Timing of observations of brood patches and 
cloacal protuberances during the 4 years was 
based on 355 captures. Females with brood 
patches and males with cloacal protuberances 
were captured from August to January, but most]) 
in October. Birds that were molting were captured 
mostly in April, but also at other times, but not in 
October and November (Fig. 2). Birds did noi 
molt and have brood patches or cloacal protuber¬ 
ances simultaneously. 
Incubation and Nestling Periods. —The incuba¬ 
tion period ranged from 12 to 14 days in length 
with an average ± SD of 13.0 ± 0.7 days (n = 
23). The nestling period ranged from 9.0 to 
14.0 days with an average of 11.7 ± 1.4 days (n = 
27) (Fig. 3). Only females were observed building 
nests and incubating eggs, while both males and 
females provisioned nestlings. Other birds in the 
group (helpers) were seen near nests with food in 
their bill, but they were not observed actually 
feeding nestlings. 
Clutch Size. —The clutch size ranged from one 
to three eggs (n = 112). Clutch size in 2003 was 
significantly larger than in the other years: 2004. 
2005. and 2006 (G = 20.028, df = 6. P = 0.003) 
(Fig. 4). 
DISCUSSION 
The breeding season of the Shrike-like Tanager 
is apparently flexible to changing environmental 
conditions and initiation of nesting can be 
advanced or delayed. This suggests photoperiod 
is not the proximal factor that stimulates onset of 
reproduction, but rather some type of resource, 
possibly food, triggers reproduction. 
Breeding Period. —The breeding season of the 
Shrike-like Tanager is similar to that reported for 
other birds from southeast and central Brazil 
(Cavalcanti and Pimentel 1988, Piratelli et al- 
2000, Marini and Duraes 2001, Duca and Marini 
2004. Marini ct al. 2007). Other passerines nested 
during the same time interval at the study site, 
including White-rumped Tanager (Cypsnagra 
hirundinacea ) (Santos and Marini 2010). Black- 
throated Saltator ( Saltator atricollis) (MAM. 
unpubl. data), several flycatchers (Lopes and 
Marini 2005a; Medeiros and Marini 2007; Marini 
ct al. 2009a. b). and the Chalk-browed Mocking¬ 
bird (Miin us satuminus) (Rodrigues 2009). The 
