Yellow-rumped Marshbird

Belonging to the family Icteridae, this striking South American passerine is easily recognized by its contrasting plumage. It is a medium-to-large icterid, measuring between 24 and 26 centimeters in length. Its plumage is characterized by a brilliant bright yellow coloration on the breast, belly, thighs, rump, and lesser wing coverts. In stark contrast, the head, back, wings, and tail are a deep sooty black or dark brownish-black. The bill is long, pointed, conical, and matte black, perfectly suited for its feeding habits. There is no significant sexual dimorphism, although females may be slightly smaller than males. Juveniles can be distinguished by their duller yellow tones, which are often washed with brown.

Geographical distribution: This species is endemic to eastern South America. Its range covers the southeastern region of Brazil (extending from Bahia and Minas Gerais south to Rio Grande do Sul), eastern Paraguay, northeastern Argentina (specifically in the provinces of Misiones, Corrientes, and Entre Ríos), and northern Uruguay. It is a sedentary, non-migratory species that remains in its established territories throughout the year.

Habitat: It primarily inhabits wet grasslands, seasonally flooded savannas, marshes, damp pastures, and agricultural fields with poor drainage. While strongly tied to freshwater bodies and emergent vegetation, it also frequently visits drier grasslands and transitional scrublands, provided there are tall perches available for vocalizing and scanning for predators.

Feeding: It is an omnivorous species with a strong insectivorous preference, particularly during the breeding season. Its diet consists mainly of invertebrates, including beetles, grasshoppers, spiders, caterpillars, and earthworms, which it captures by walking on the ground or probing into mud and dense vegetation. It also consumes seeds, cultivated grains, and occasionally small vertebrates such as tiny frogs and lizards.

Behavior: Highly gregarious outside the breeding season, it often aggregates in noisy flocks that can number dozens of individuals. It is common to see this species foraging in mixed-species flocks alongside Pseudoleistes virescens. Its flight is direct but heavy, characterized by steady wingbeats. This bird is extremely vocal; individuals regularly perch on tall shrubs, fence posts, or utility wires to deliver a loud, melodious, and complex song filled with liquid whistles and metallic notes, used for territorial defense and social cohesion.

Nesting: Its reproductive strategy is notable for incorporating cooperative breeding, where the breeding pair is frequently assisted by helpers (often offspring from previous seasons) that assist in feeding the nestlings and defending the nesting site. They build a deep, cup-shaped nest made of grass stems, roots, and wet mud, which hardens to provide structural support. The nest is typically hidden in dense marsh vegetation or low thorny shrubs. The female lays 3 to 4 whitish eggs speckled with reddish-brown spots. Incubation lasts around 14 days and is performed mainly by the female. The nests of this species are heavily targeted by the brood parasite Molothrus bonariensis.

Conservation status: It is currently listed as Least Concern (LC) on the IUCN Red List. Although its global population is considered stable and its range is extensive, local populations are threatened by habitat loss and degradation resulting from the drainage of wetlands, agricultural expansion, and the intensive use of agrochemicals, which limits food availability.