### Identification The male Chestnut-capped Blackbird is a showstopper of the South American marshlands. It features a sleek, jet-black body that provides a stark canvas for its namesake: a crown and throat of rich, burnt-sienna that looks as though it were dipped in wet mahogany paint. Measuring about 18–19 cm, they possess the classic sharp, conical bill of the Icterid family. Females are far more cryptic, sporting olive-brown plumage with fine dusky streaking—a necessary camouflage for life in the reeds. To tell them apart from the similar Unicolored Blackbird, look specifically for that vibrant rufous cap; if the bird is entirely black, it’s not your subject.
### Habitat & Range This species is a specialist of the wet lowlands, ranging from eastern Brazil and Bolivia through the Pampas of Argentina and Uruguay. They are strictly bound to water, favoring freshwater marshes, reed beds, and flooded grasslands. Interestingly, they have become highly successful in man-made landscapes, particularly flooded rice plantations, which mimic their natural marshy haunts.
### Behaviour Highly gregarious and social, these birds are rarely seen alone. They are colonial nesters, with dozens of pairs weaving cup-shaped nests into the same patch of rushes. In the field, look for the males’ dramatic "song-spread" display: they puff out their feathers, spread their tails, and lean forward to emit a series of wheezy, metallic whistles and buzzes. Their flight is direct and rhythmic, often moving in large, synchronized groups.
### Diet They are opportunistic generalists. During the breeding season, they forage heavily for protein-rich insects and spiders gleaned from aquatic vegetation. In the winter months, they pivot toward a granivorous diet, descending in noisy clouds upon grain fields to feast on seeds and fallen rice.
### Fascinating Fact The scale of their social structure is staggering; during the non-breeding season in Uruguay and Argentina, "mega-flocks" can form that contain over a million individuals, momentarily turning the sky black as they move between roosting sites.