Breeding biology and reproductive performance of the pearly-bellied seedeater (Sporophila pileata) in the Brazilian Pampa: evidence of population-level variation

The natural history of capuchino seedeaters ( Sporophila spp.), a group largely restricted to southern South America, has received increasing attention in recent years, mainly due to the urgent need to generate biological information to support conservation strategies in rapidly disappearing grassland ecosystems. Most available studies have been conducted in the Pampas of Brazil and Argentina and in the Cerrado of central Brazil. However, important gaps remain regarding population-level variation in life-history traits, despite its potential relevance for conservation planning. The pearly-bellied seedeater ( Sporophila pileata ), recently split from the copper seedeater ( S . bouvreuil ), represents an excellent model for investigating population differences, given its wide and disjunct distribution and its partial overlap with other forms formerly included within S . bouvreuil . While basic breeding information is available for a population breeding in the Cerrado, no data exist for the disjunct population that breeds in the southern Brazilian grasslands of South America, one of the most threatened ecosystems in the Southern Hemisphere. Here we describe nest characteristics, eggs, nestlings, and breeding parameters of S . pileata , including breeding success, clutch size, hatching rate, annual nestling production, and nestling sex ratio, based on monitoring of 73 nests during the 2022–2023 and 2023–2024 breeding seasons in southern Brazil. We compare our estimates of breeding success with those reported for other Sporophila species breeding in southern Brazilian grasslands and with previous results for S . pileata from the Cerrado Biome. Survival estimates differed according to the analytical method employed, and we found comparatively low hatching rates in the studied population. Our results highlight marked population-level differences in breeding performance and reinforce the importance of incorporating population-specific information into conservation strategies, rather than focusing exclusively on species-level assessments. For grassland conservation in the Pampas, we emphasize the need to maintain structurally and floristically suitable grasslands and to promote large areas under sustainable-use protected areas encompassing key breeding sites of this species.