The Wilson Journal o f Ornithology 124(2):286—291, 2012 
NEST AND EGGS OF THE MARSH ANTWREN (STYMPHALORNIS 
ACUT1ROSTRIS ): THE ONLY MARSH-DWELLING THAMNOPHILID 
BIANCA L. REINERT, 1 6 RICARDO BELMONTE-LOPES. 12 MARCOS R. BORNSCHEIN." 
DAIANE D. SOBOTKA, * 1 - 3 LEANDRO CORREA. 1 ’ MARCIO R. PIE. 4 AND MARCO A. PIZCf 
ABSTRACT.—We describe the nest and eggs of the Marsh Antwren {Stymphalornis acutirnstris), a recently described 
species which is the only member of the Thanmophilidae restricted to marsh habitats. We conducted 1,560 hrs of nes: 
searching in tidal marshes ot southern Brazil and found 178 nests. All nests were of dry fibers, straw's, and silk. Nineteen 
plant species were used for nest attachment. All nests had a clutch of two white eggs with several irregular brown spot' 
scattered over the entire egg. concentrated at the middle or the largest pole. The strategy of nest attachment to vertical 
structures used by the Marsh Antwren was previously unknown in the Thamnophilidae. Received 14 June 2011. Accepted 
12 December 2011. 
The vast majority of species in the Thamnophi- 
litlae live in forests throughout the Neotropies 
(Zimmer and Isler 2003); the Marsh Antwren 
(Stymphalornis acutirnstris) is the only species 
restricted to marsh habitats (Zimmer and Isler 
2003). The Marsh Antwren was described as a new 
species and genus by Bornschein et al. (1995). and 
occurs only along the coast of the states of Paratui 
and Santa Catarina in southern Brazil (Reinert et al. 
2007). It is presently classified as ‘endangered’ 
(BirdLife International 2010). We found a large 
number of nests of this species during a multiyear 
study of the population ecology of the Marsh 
Antwren. We describe for the first time the nest 
structure and type of attachment to vegetation, as 
well as the eggs of the Marsh Antwren. 
METHODS 
Field work was conducted from January 2006 
to March 2010 in tidal marshes at Guaratuba Bay 
1 Maler Natura-Instituto de Estudos Ambientais. Rua 
Lamenha Lins 1080, CEP 80250-020. Curitiba. Parana. 
Brazil. 
Programa de P6s-Gradua?3o cm Zoologia, Departa- 
mento de Zoologia. Universidade Federal do Parana, Centro 
Politecnico. Jardim das Americas. Caixa Postal 19073, CEP 
81531-990. Curitiba, Parana. Brazil. 
Programa de Pos-Graduuyao cm Ecologia e Conserv 
?ao, Universidade Federal do Parana. Centro Politdcnic 
Jardim das Americas, CEP 81531-990. Curitiba. Panin 
Brazil. 
1 Laboratory de Dinamica Evolutiva c Sistemas Cot 
plexos, Departamcnto dc Zoologia, Universidade Feder 
do Pa rand, Centro Politic,lieu, Ja,dim das Americas, CE 
81531-990. Curitiba, Parana, Brazil. 
'UNESP-Universidade Estadual Paulista. Dcpartamem 
de Zoologta. CEP 13506-900. Rio Clam. Sao Paulo, Brazi 
Corresponding author; e-mail: 
biancareinert@yahoo.com.br 
(Folharada Island: 25 52' 00" S, 48 43' 26” W. 
15.7 ha; Jundiaquara Island: 25 52’ 28" S. 48 
45' 33" W, 11.6 ha; and the Claro River: 25 52' 
26" S, 48 45' 41" W. 8.2 ha), municipality of 
Guaratuba, coast of the Stale of Parana, southern 
Brazil. A detailed description of the tidal marshes 
in this region has been presented bv Rcinen el al. 
(2007). 
Nest searches were conducted daily during the 
reproductive season using the focal-animal meth¬ 
od (Altmann 1974). We made ad libitum obser¬ 
vations (Allmann 1974) of birds collecting 
materials for nest building during these searches. 
All complete nests found were assigned to a 
breeding pair (all pairs in the study area were 
previously color-banded), and measured in the 
field with a caliper to the nearest 0.1 cm before 
onset of incubation or after predation or nesl 
abandonment were confirmed. A nest was con¬ 
sidered abandoned after at least 3 weeks without 
any modification of previous conditions, and 
regarded as completed when an incubation 
chamber was present. We measured the height 
above ground for some nests as soon as they were 
completed and when they were collected. 
used only the initial measurement for calculating 
mean values when nest height varied during the 
breeding season. 
We calculated nest and incubation chamber 
volumes following Moller (1982): nest material 
volume = nest volume minus nest cup volume 
and volume = 4/3 X k X largest radius 2 X height 
X the fraction of an ellipsoid with the fraction 
assigned to Zi. We recorded plant species where 
nests were attached and if it was green or dry 
vertical (between 71 and 90 ), horizontal (0-15 I. 
or inclined. Plant species identification folio"'' 
Bornschein (2001) and Reinert et al. (2007), but 
286 
