Rusty-collared Seedeater

Exhibiting a pronounced sexual dimorphism, this small passerine bird measures approximately 11.5 to 12.5 centimeters in length and weighs between 7.5 and 14 grams. The adult male boasts a striking and highly distinctive plumage, characterized by a jet-black head that contrasts sharply with a bright white throat and a pale cinnamon or whitish nuchal collar. Across the upper breast, it displays a well-defined, broad black pectoral band, while its belly, flanks, and rump transition into warm tones of cinnamon-rufous. Its wings are dark charcoal with small, diagnostic white specular patches at the base of the primary feathers. Conversely, the female presents a much more inconspicuous, cryptic coloration, dominated by warm olive-brown upperparts and pale buffy-ochre underparts, completely lacking the male’s dramatic black and white facial markings. Both sexes share a stout, short, and strongly conical bill of a dark gray or blackish hue, which is evolutionary adapted for cracking open tough seeds.

Exhibiting a pronounced sexual dimorphism, this small passerine bird measures approximately 11.5 to 12.5 centimeters in length and weighs between 7.5 and 14 grams. The adult male boasts a striking and highly distinctive plumage, characterized by a jet-black head that contrasts sharply with a bright white throat and a pale cinnamon or whitish nuchal collar. Across the upper breast, it displays a well-defined, broad black pectoral band, while its belly, flanks, and rump transition into warm tones of cinnamon-rufous. Its wings are dark charcoal with small, diagnostic white specular patches at the base of the primary feathers. Conversely, the female presents a much more inconspicuous, cryptic coloration, dominated by warm olive-brown upperparts and pale buffy-ochre underparts, completely lacking the male’s dramatic black and white facial markings. Both sexes share a stout, short, and strongly conical bill of a dark gray or blackish hue, which is evolutionary adapted for cracking open tough seeds.

Geographical distribution: This species is native to the lowlands of South America, occupying an extensive range across several countries. It is widely distributed throughout central, southeastern, and southern Brazil, extending westward into the lowlands of eastern Bolivia, across the entirety of Paraguay, throughout northern and western Uruguay, and into the northeastern provinces of Argentina, where its southernmost distribution limits reach the humid pampas of Buenos Aires Province. Its presence is highly concentrated along major river basins, including the Paraná, Paraguay, and Uruguay systems.

Habitat: It primarily colonizes humid grasslands and transitional ecotones between terrestrial and aquatic environments. It is commonly found in freshwater marshes, seasonally flooded savannas, swamps, dense reed beds, margins of lakes, riparian shrublands, and agricultural areas with stagnant water or rice paddies. It exhibits a strong preference for low-elevation habitats, generally occurring below 800 meters above sea level, where the presence of tall, seed-producing grasses and dense reeds offers both abundant foraging opportunities and critical shelter.

Feeding: Primarily granivorous, its diet relies heavily on the seeds of various wild grasses and herbaceous plants, with a strong preference for the family Poaceae. To feed, it agilely climbs grass stems, using its weight to bend them down and pluck the seeds directly from the inflorescences. During the nesting season, it opportunistically supplements this seed-based diet with small invertebrates, including insects and larvae, which provide vital protein required for the rapid development of its nestlings.

Behavior: During the non-breeding autumn and winter months, it exhibits gregarious behavior, often joining large, mixed-species flocks with other Sporophila seedeaters to forage in open pastures. However, with the onset of the spring breeding season, it becomes highly territorial and socially monogamous. Males are renowned for their melodious, intricate, and high-pitched territorial song, which they deliver from prominent perches such as fence posts, tall reeds, or outer shrub branches to defend their territory and court females. Its flight pattern is typically undulating and low, seldom flying long distances without seeking cover in thick vegetation.

Nesting: Breeding occurs predominantly from late spring through summer, synchronizing with peak seed and insect abundance. The construction of the nest is performed almost exclusively by the female, who builds a delicate, neat, cup-shaped structure. This nest is woven from fine grasses, rootlets, hair, and bound together with spider silk to provide elasticity, and is suspended at low heights in reeds, shrubs, or tall grass tussocks, often directly over or near water. The female lays a clutch of 2 to 3 eggs, which are pale greenish-white or bluish-white, heavily speckled with dark brown and lilac spots. Incubation is carried out solely by the female and lasts for 10 to 13 days. After hatching, both parents actively provision the altricial chicks, which fledge and leave the nest approximately two weeks later.

Conservation status: It is currently classified as a species of Least Concern (LC) on the IUCN Red List of Threatened Species. While its global population is considered stable and it occupies a vast geographical range, certain local populations face pressures due to habitat loss caused by the drainage of wetlands for agricultural conversion and urban sprawl, alongside the persistent threat of illegal trapping for the wild caged-bird trade, driven by the male´s highly prized singing abilities.