Nest, eggs, and nest placement of the Brazilian endemic Black-bellied Seedeater (Sporophila melanogaster).
Abstract: We present the first detailed description of the nest and eggs of the Black-bellied Seedeater (Sporophila melanogaster) based on observation of 64 nests in three areas of grassland in southeastern Santa Catarina and northeastern Rio Grande do Sul states, Brazil. The nests were found from November through March. The nest has the shape of a shallow basket, constructed with portions of dried grasses and strung with spider webs. Half of the nests were constructed in Ludwigia sericea (Onagraceae), and the other half were in 15 other plant species. Of these, the most important were Eupatorium polystachyum (10%) and Achyrocline vauthieriana (6%) (Asteraceae). Only the female constructs the nest. The eggs are ovoid and colored whitish with brownish-purple spots near the wider portion. Clutch size was two eggs, rarely three.
Article Type: Report
Subject: Birds (Eggs and nests)
Birds (Research)
Authors: Rovedder, Cristiano Eidt
Fontana, Carla Suertegaray
Pub Date: 03/01/2012
Publication: Name: The Wilson Journal of Ornithology Publisher: Wilson Ornithological Society Audience: Academic Format: Magazine/Journal Subject: Biological sciences Copyright: COPYRIGHT 2012 Wilson Ornithological Society ISSN: 1559-4491
Issue: Date: March, 2012 Source Volume: 124 Source Issue: 1
Topic: Event Code: 310 Science & research
Geographic: Geographic Scope: Brazil Geographic Code: 3BRAZ Brazil
Accession Number: 285207260
Full Text: The Black-bellied Seedeater (Sporophila melanogaster) is endemic to Brazil (Sick 1997), where it is listed as endangered (MMA 2003). Globally, it is considered a near-threatened species (IUCN 2010). The entire population in the breeding season is confined to a small grassland area in Planalto das Araucdrias, in northeastern Rio Grande do Sul (RS) and southeastern Santa Catarina (SC) states (Ridgely and Tudor 1989, Rosario 1996, Sick 1997, Fontana et al. 2008). These seedeaters migrate north after the breeding season, toward southeast and central Brazil, passing through Parana and Sao Paulo states, to reach Minas Gerais, southern Goias, and the Distrito Federal, where they overwinter (Ridgely and Tudor 1989, Sick 1997).

Aspects of the reproductive biology of several species of Sporophila have been described in the last decade, including S. caerulescens (Francisco 2006), S. hypoxantha (Di Giacomo 2005, Facchinetti et al. 2008, Franz and Fontana 2010), S. collaris (Facchinetti et al. 2008), S. leucoptera (Francisco 2009), S. lineola (Oliveira et al. 2010), and S. palustris (Jacobs et al. 2010). However, there is no published information about the reproductive biology of S. melanogaster. We describe for the first time the nest and eggs of the Black-bellied Seedeater, as well as the plant species used to support nests.

METHODS

Our study was conducted in high-altitude grasslands in the southern portion of the Atlantic 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 Agua Branca Stream (28[degrees] 35' S, 50[degrees] 24' W; Bota Jesus, Rio Grande do Sul), (2) wet grasslands of the Santana River (28[degrees] 29' S, 50[degrees] 43' W; Bota Jesus, Rio Grande do Sul), and (3) grasslands of Coxilha Rica (28[degrees] 18' S, 50[degrees] 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 were 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 Tecnologia da Pontificia Universidade Catolica do Rio Grande do Sul (PUCRS).

Plants that supported nests were measured in the field, and some were collected for identification. 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 [+ or -] 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.

RESULTS

Nests were small cups, classified as low cup/ fork (fork basket placed low). They were constructed of thin plant fibers, mostly Eragrostis airoides, and small portions of Paspalum notatum, Briza uniolae, and Eustachys uliginosa (all Poaceae) (Fig. 1). These fibers were connected by large amounts of spider webs, which also adfixed the nest to the supporting plant.

[FIGURE 1 OMITTED]

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 polystachyum (Asteraceae) with 10.9% (n = 7), and Achyrocline vauthieriana (Asteraceae) with 6.2% (n = 4). Other less used plant species were: Andropogon lateralis (n = 3), Erechtites hieraciifolius (n = 3), Baccharis coridifolia (n = 2), Eupatorium betoniciiforme (n = 2), Pteridium aquilinum (n = 2), and Vernonia spp. (n = 2). Baccharis caprariifolia, Erechtites valerianifolius, Eupatorium bupleurifolium, E. candolleanum, and Paspalum exaltatum were each recorded once supporting nests. Two species of supporting plants were not identified. Plant measurements taken were: height = 81 [+ or -] 25.3 cm (range = 38-170; n = 49), stem thickness = 5.9 [+ or -] 3.31 mm (range = 1-20.9; n = 49), largest crown diameter = 41.4 [+ or -] 23.7 cm (range = 9-11.2; n = 48), and smallest crown diameter = 31.1 [+ or -] 10.1 cm (range = 7-69; n = 48). Nests were built next to the main trunk in 81% of the records (n = 49). The distance from the nest to the edge of the plant was 12.4 [+ or -] 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 yellowish blotches and stripes (Sepia 219 and Burnt umber 22 [sensu Smithe 1975]), as well as smaller spots were generally more concentrated at the larger end (Fig. 2). Egg measurements (n = 8) were: length = 17.5 [+ or -] 0.43 (range = 16.9-18.3) and width = 12.2 [+ or -] 0.35 mm (range = 11.7-12.8). Nests had little variability in shape and measurements, especially in the internal chamber. However, height above the ground was variable which could be the result of the need to elevate the nest above the water level in the wetlands (Table 1).

[FIGURE 2 OMITTED]

DISCUSSION

Nests of S. melanogaster resemble those of its congener S. hypoxantha in shape, structure, and measurements (Di Giacomo 2005, Franz and Fontana 2010); the two species are sympatric in part of their breeding ranges and both use similar nest-support plants, including Eupatorium polystachyum and Baccharis caprariifolia (Franz and Fontana 2010). However, our data indicated that S. melanogaster preferred Ludwigia sericea for nest sites. Nest construction is by the female, as for other species of Sporophila (e.g., S. leucoptera, S. hypoxantha, S. lineola). The number of eggs laid per clutch is also similar (Di Giacomo 2005, Francisco 2009, Franz and Fontana 2010, Oliveira et al. 2010).

The literature indicates Sporophila melanogaster breeds only in wetlands (Machado et al. 1998, Bencke et al. 2003, Machado et al. 2008), despite a lack of specific studies on the nesting behavior of the species with one exception (Rovedder 2011). However, this species can nest in dry and natural portions of steep fields (using Eupatorium polystachyum bushes) near drainages or wetlands where use by cattle or people is infrequent. This could be an adaptation to loss of wetlands and conversion to crops; human stresses, such as livestock grazing or agriculture could create inappropriate habitats for Black-bellied Seedeaters.

Nesting-plant species preferences by S. melanogaster are suggested based on the proportion of the first and the second most frequently used plant, and also by quantitative studies (Rovedder and Fontana in prep.). This knowledge, as well as detailed description of the nest and eggs of the Black-bellied Seedeater, is important for development of new studies on the species' life history to benefit conservation of this threatened endemic Brazilian species.

ACKNOWLEDGMENTS

We are grateful to I. I. Boldrini and staff (UFRGS) for assistance in identifying plant species; Ismael Franz, Jonas Rosoni, Marcio Repenning, and Mariana L. Goncalves for field assistance; two anonymous reviewers and C. E. Braun for manuscript improvement; the Fundacao Grupo Boticario de Protecao a Natureza and Neotropical Grassland Conservancy for financial support to the project; CNPq for a scholarship to C. E. Rovedder; and the Museu de Ciencias e Tecnologia da PUCRS for logistical help.

Received 23 November 2010. Accepted 11 October 2011.

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Cristiano Eidt Rovedder (1) and Carla Suertegaray Fontana (1, 2)

(1) Laboratorio de Omitologia, Museu de Ciencias e Tecnologia, Programa de Pos-Graduacao em Zoologia, Faculdade de Biociencias da Pontificia Universidade Catolica do Rio Grande do Sul, PUCRS, Caixa Postal: 1429. 90619-900, Porto Alegre, RS, Brazil.

(2) Corresponding author; e-mail: carla@pucrs.br
TABLE 1. Measurements (cm) of 48 nests of the Black-bellied Seedeater
(Sporophila melanogaster) in Brazil.

Variables                               Mean     SD     Min    Max

Largest external diameter                6.55    0.57    5.5    8
Smallest external diameter               6.13    0.45    5.3    7.3
Largest internal diameter of chamber     4.55    0.37    3.9    5.5
Smallest internal diameter of chamber    4.24    0.33    3.5    5
External height                          5.14    0.57    3.5    6.8
Internal height (depth)                  3.34    0.42    2.3    4.1
Height above ground (n = 54)            31.5    10.83   15     60
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