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THE WILSON JOURNAL OF ORNITHOLOGY • Vol 124. No. 1. March 2012 
Forest Biome. These are wide areas of grasslands 
where cespitose grasses predominate (Boldrini 
et al. 2009), generally >800 m asl with small 
patches of Araucaria forest and wetlands or 
natural drainages (Klein 1981, Rambo 2000. 
Porto 2002). 
Nest searches were conducted from October 
through March during three breeding seasons 
(2007/2008. 2008/2009, and 2009/2010) in three 
areas: (1) wet grasslands of the Ague Branca 
Stream (28 35' S, 50° 24' W: Bom Jesus, Rio 
Grande do Sul), (2) wet grasslands of the Santana 
River (28 29' S, 50 43' W; Bom Jesus, Rio 
Grande do Sul), and (3) grasslands of Coxi/ha 
Rica (28' 18' S, 50 ; 16' W; Lages, Santa 
Catarina), 
We collected data on the supporting plant for 
64 nests. Fifty nests were in the area of Agua 
Branca Stream, eight nests w'ere in the grasslands 
of Coxilha Rica , and six nests were in the wet 
grasslands of the Santana River. We collected 
data on nest plant composition of 54 nests and 
measured 49. as nests were predated or destroyed 
during the nesting period, or immediately after 
fledging. Classifications of nests followed Simon 
and Pacheco (2005). Nests were collected after 
they were measured, and deposited in the 
Collection of Birds at the Museu de Ciencias e 
Tecnalogia da Pontifuia Universidade Catdlica 
do Rio Grande do Sul (PUCRS). 
Plants that supported nests were measured in 
the field, and some were collected for identifica¬ 
tion. Measurements taken were based on Ralph et 
al. (1996): height of the plant, minimum and 
maximum diameter of the crown, and stem 
thickness (at the height where the nest was 
attached). Nests, supporting plants, and eggs were 
measured with metal calipers (accurate to 
0.02 mm) and a millimeter ruler. We used 
descriptive statistics (mean ± SD) to compare 
measurements. The color of the eggs followed 
Smithe (1975). Mass of eggs was not measured. 
Direct observations of six nests found in the 
construction stage were conducted to record adult 
behaviors during nest construction. 
rvc.su 1.1 s 
Nests were small cups, classified as low c 
fork (fork basket placed low). They w 
constructed of thin plant fibers, mostly Eragro. 
airoides, and small portions of Pas P alum notati 
Bnza umolae. and Eustachys uliginose, ( 
Poaceae) (F,g. 1 ). These fibers were conned 
FIG. I. Nest of the Black-bellied Seedeater in Eupa- 
toriam betoniciiforme (Ilsi Boldrini, pers. comm.), Vacaria. 
Rio Grande do Sul, Brazil. (Photograph by Cristiano 
E. Rovedder). 
by large amounts of spider webs, which also 
ad fixed the nest to the supporting plant. 
Sixteen different plant species were used to 
support nests. Most often used species were 
Ludwigia sericea (Onagraceae) with 50% of the 
total nests (n = 32), followed by Eupatorium 
polysiachyum (Asteraceae) with 10.9% (// = 7). 
and Achyrocline vauthieriana (Asteraceae) with 
6.2% (n - 4). Other less used plant species were: 
Andropogon lateralis (n = 3). Erechtites hier- 
aciifolius (n = 3), Bacckaris coridifolia (n - ->• 
Eupatorium betoniciiforme (n = 2). Pteridium 
aquilinum ( n = 2), and Vemonia spp. (« = -)• 
Baccltaris caprariifolia, Erechtites valerumfolm. 
Eupatorium bupleurifolium, E. candolleanum. 
and Paspalum exaltation were each recorded once 
supporting nests. Two species of supporting planb 
were not identified. Plant measurements taken 
were: height =■ 81 ± 25.3 cm (range = 38-170: 
n = 49). stem thickness = 5.9 ± 3.31 mm (range 
= 1-20.9: n = 49), largest crown diameter = 41.4 
± 23.7 cm (range = 9-11.2; n = 48). and 
smallest crown diameter = 31.1 ± 10.1 cm (range 
= 7-69; n = 48). Nests were built next to the 
main trunk in 81% of the records (n = 49). Tire 
distance from the nest to the edge of the plant was 
12.4 ± 9.16 cm (range = 2-42: n = 22). 
Nest construction started at the beginning 
of November, and only females were recorded 
constructing the nests (n = 6 nests; 14.4 hrs of 
observation). Females laid two (88.6%: n = 39) 
to three eggs per clutch (11.4%; n = 5). The 
eggs were ovoid with background color ranging 
from white to beige. Irregular brownish-purple or 
