SHORT COMMUNICATIONS 879 The Wilson Journal of Ornithology 120(4):879–883, 2008 Parental Care in Tawny-bellied (Sporophila hypoxantha) and Rusty-collared (S. collaris) Seedeaters Carolina Facchinetti,1 Alejandro G. Di Giacomo,2 and Juan C. Reboreda1,3 ABSTRACT.—The genus Sporophila (Emberizidae) The genus Sporophila (Emberizidae) com- comprises species of small finches characterized by prises 31 species of small finches that inhabit marked sexual dichromatism, which in birds is posi- grassy open and semi-open habitats from tively associated with extent of female bias in parental care. We analyzed differences in parental care in Taw- Mexico to central Argentina (Meyer de ny-bellied (S. hypoxantha) and Rusty-collared (S. col- Schauensee 1952, Ridgely and Tudor 1989). laris) seedeaters. We video-recorded nest activity dur- All Sporophila species are characterized by a ing incubation and when young were 2–4 and 7–9 marked plumage-color dimorphism with days of age. Females of both species built the nest and males strongly patterned and colorful, and fe- incubated the eggs alone. Female Tawny-bellied Seed- males duller and similar between species eaters: (1) incubated 59% of the time, (2) had a higher frequency of nest visits than males when chicks were (Ridgely and Tudor 1989). Variation in mel- 2–4 days of age, and (3) their visits were longer be- anin-based dichromatism in birds is positively cause after feeding they remained in the nest brooding associated with extent of gender bias in pas- the chicks. There were no gender differences in fre- sive brood defense (Owens and Hartley 1998). quency of nest visits when chicks were 7–9 days of Males of dichromatic species are less likely to age, but visits of females were longer than those of participate in nest building (Soler et al. 1998) males. Female Rusty-collared Seedeaters: (1) incubat- and to share incubation with females (Verner ed 51% of the time and (2) had a higher frequency of nest visits when chicks were 7–9 days of age. Both and Willson 1969). males and females brooded chicks and there were no The reproductive biology of Sporophila gender differences in frequency and length of nest vis- seedeaters is little studied and most research its when chicks were 2–4 days of age. Parental care in was in Central America (i.e., Gross 1952, both species is female biased, but the extent of male Skutch 1954, Alderton 1961, Stutchbury et al. care is slightly higher in Rusty-collared than in Tawny- 1996, but see Marcondes-Machado 1997, bellied seedeaters. Received 4 February 2008. Accept- ed 29 April 2008. Francisco 2006). These studies indicate that most Sporophila seedeaters are socially mo- nogamous and have biparental care, but do not The most common mating pattern among report details of sexual differences in parental birds is social monogamy with biparental care care. (Lack 1968, Silver et al. 1985, Neudorf 2004). The reproductive biology of Tawny-bellied However, there is a considerable variation in Seedeater (S. hypoxantha) and Rusty collared type and extent of male care within monoga- Seedeater (S. collaris) is virtually unknown, mous species, as males may or may not de- except for the work of Di Giacomo (2005). fend territories, build the nest, incubate the Tawny-bellied Seedeaters are included within eggs, brood and deliver food to the nestlings, the ‘‘capuchinos’’, a monophyletic group of and assist fledglings after they leave the nest 11 species (Lijtmaer et al. 2004) that share a (Clutton-Brock 1991). similar male plumage coloration pattern (Ridgely and Tudor 1989). Rusty-collared 1 Departamento de Ecologı´a, Gene´tica y Evolucio´n, Seedeaters are included in a different clade Facultad de Ciencias Exactas y Naturales, Universidad than Tawny-bellied Seedeaters (Lijtmaer et al. de Buenos Aires, Pabello´n II, Ciudad Universitaria, 2004) allowing us to compare gender differ- C1428EGA, Buenos Aires, Argentina. ences in parental care between species that are 2 Departamento de Conservacio´n, Aves Argentinas/ relatively distant within the genus. The objec- Asociacio´n Ornitolo´gica del Plata, Matheu 1246, C1249AAB Buenos Aires, Argentina. tives of our study were to: (1) analyze the ex- 3 Corresponding author; e-mail: tent of gender bias in parental care in S. hypo- [email protected]. xantha and S. collaris, and (2) compare gen- 880 THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 120, No. 4, December 2008 der differences in parental care between these six nests during incubation (12 hrs of video species. records) for Tawny-bellied Seedeaters, 13 nests with chicks 2–4 days of age (36 hrs), METHODS and five nests with chicks 7–9 days of age (12 Study Area.—The study was conducted at hrs). We video recorded four nests of Rusty- Reserve El Bagual (26Њ 10Ј S; 58Њ 56Ј W), in collared Seedeaters during incubation (8 hrs), the Province of Formosa, Argentina, during four nests with chicks 2–4 days of age (8 hrs), breeding seasons 2004–2005 and 2005–2006. and six nests with chicks 7–9 days of age (20 This 3,300-ha reserve is in the region of the hrs). We observed both members of the pair eastern or humid Chaco. Average annual rain- at all of these nests. We video recorded each fall in the area is 1,500 mm with mean month- nest throughout incubation during morning ly temperature varying from 16.9Њ C in July (between 0700 and 1100 hrs) and afternoon to 26.7Њ C in January. (between 1500 and 1900 hrs). We video re- Study Species.—Tawny-bellied Seedeaters corded nests only during the morning for the are sexually dichromatic but genders do not chick stages. differ in body size (ϳ8–9 g). They are resi- Data Analysis.—We watched the videotapes dents at our study site and nest in dry grass- in the laboratory and identified the gender of lands of Elionurus muticus and Imperata the parent, number of times (to the nearest brasiliensis or Andropogon lateralis, and in sec) it landed at, entered, exited, and departed wet grasslands of Paspalum intermedium and from the nest, and activity at the nest (incu- Sorghastrum setosum. Laying starts during the bation, feeding, or brooding). We measured second half of October and continues until the the length of each activity in those visits second half of March. The nest is a deep semi- where there were two different behaviors (i.e., spherical open cup built at a height of ϳ70 feeding and brooding). We calculated the fre- cm above ground level. Clutch size is 2–3 quency of visits to the nest (nest visits/hr) for eggs; incubation starts with the laying of the each parent, average length of the visits (sec), penultimate egg and lasts 11–12 days. Young time elapsed between visits (sec), and propor- fledge when they are 9–10 days of age (Di tion of time spent incubating eggs, and feed- Giacomo 2005). ing and brooding chicks. Rusty-collared Seedeaters are sexually di- We used nonparametric statistics for anal- chromatic and males and females do not differ yses due to lack of normality of the data and in body size (ϳ12–13 g.). They are residents small sample sizes of the groups. Statistical at our study site and nest in wetlands of Cy- analyses were performed using StatView Ver- perus giganteus from early November to early sion 5.0 statistical software (SAS Institute April. The nest is a semispherical open cup 1998). All P-values are two-tailed with alpha built at a height of 1–1.5 m above ground lev- (␣) set at 0.05. Data are presented as means el. Clutch size is 2–3 eggs; incubation starts Ϯ standard errors. We provide confidence in- with laying of the penultimate egg and lasts tervals when comparisons yield a nonsignifi- 12–13 days. Young leave the nest when they cant result because of small sample sizes are 9–12 days of age (Di Giacomo 2005). (Colegrave and Ruxton 2003). Data Collection.—We searched for nests during the breeding season and visited nests RESULTS daily or every other day to identify start of Tawny-bellied Seedeaters.—Females built laying and date of hatching. We recorded nest- the nest and incubated the eggs alone. We did building activity in 18 nests of Tawny-bellied not find differences in frequency and length Seedeaters and 10 nests of Rusty-collared of incubation bouts between morning and af- Seedeaters. We recorded the gender of the in- ternoon (Wilcoxon Signed Rank tests, fre- dividual that carried nest material during 3–4 quency: z ϭϪ0.94, P ϭ 0.35, n ϭ 6; length: consecutive trips for each nest (ϳ15–25 min z ϭϪ0.10, P ϭ 0.92, n ϭ 6). Females spent of observation/nest). We video-recorded nest 59 Ϯ 5% of the time at the nest including activity using a Sony Hi8 CCD video camera observations of morning and afternoon to- placed 1.5–2 m from the nest. Video records gether; frequency and length of incubation lasted between 2 and 4 hrs. We video recorded bouts were 2.3 Ϯ 0.2 bouts/hr and 16.5 min SHORT COMMUNICATIONS 881 chicks in nests monitored at this stage was 1.9 Ϯ 0.5 (n ϭ 13). There were no gender differences in fre- quency of nest visits when chicks were 7–9 days of age (z ϭϪ0.7, P ϭ 0.50, n ϭ 5, mean Ϯ SD females: 4.2 Ϯ 1.4, males: 4.8 Ϯ 2.9, 95% confidence interval: Ϫ3.8 – 2.6; Fig. 1), but females still had significantly longer visits than males (z ϭϪ2.0, P ϭ 0.043, n ϭ 5; Fig.