Black-and-white Monjita Heteroxolmis dominicana Scientific name definitions

This is a rare and declining species and as far as monjitas go, it is one with an unusual shape, it was formerly classified in its own genus Heteroxolmis. This monjita is relatively large but slim, with a distinctly long tail. It also is more strongly sexually dichromatic (male and female look different) than other monjitas. The male is strikingly white on the head, upperparts and underparts with contrasting black wings and tail; the wing showing a striking white wingtip. The range of this species has undergone a drastic constriction and now is found in isolated spots, where once it ranged throughout the Pampas region from southern Paraguay and S Brazil south to central Buenos Aires Province. It requires marshy grassland, often adjacent to drier grassland and shrubby areas. This habitat mix has declined precipitously in southern South America through various changes in land use associated with agriculture. Currently the strongholds for this species include eastern Uruguay, and Corrientes in Argentina. Of particular interest is that this flycatcher has been considered to sometimes to be followed by foraging groups of the equally rare Saffron-cowled Blackbird (Xanthopsar flavus), this association described from Rio Grande do Sul in Brazil has not yet adequately been explained. They may somehow be able to feed more efficiently together than alone perhaps?

20–20·5 cm. Male is mostly white, with pale greyish smudging on head and back; wings black, outer third of primaries white; tail rather long, black; iris dark; bill and legs black. Differs from X. irupero in larger size, less pure white colour, more black in wings, all-black tail. Female has crown and back brownish-grey, prominent white scapulars and rump. Juvenile has rusty back.

SE Brazil (Paraná, Santa Catarina, Rio Grande do Sul), Uruguay and W & NE Argentina (Corrientes, E Entre Ríos and NE Buenos Aires); unconfirmed records in Paraguay; formerly more widespread.

Marshes and bogs with sedge (Cyperus and Eryn­gium), open or burned areas, also landward side of coastal sand dunes; often forages in adjoining grassland. Generally below 500 m, occasionally to 1000 m.

Resident.

Insects. Drops from low perch to ground for prey. Foraging birds often associated with Saffron-cowled Blackbird (Xanthopsar flavus) flocks, reasons unknown.

Usually silent; soft, somewhat querulous “weeyrt” or “wurrt” call, especially when agitated.

Nests found Oct–Dec in SE Brazil (Rio Grande do Sul); late Sept to Dec in Argentina. Nest relatively bulky, substantial open cup of dry grasses, coarse stems and often some leaves, lined with finer grasses, a few feathers and/or wool, well hidden in low bush within small clump of marsh vegetation, or on clump of grass; five nests had mean length c. 16·4 cm, width 11·4 cm, height 7·5 cm, cup width 8·5 cm, cup depth 4·8 cm. Clutch 3–4 eggs; no information on incubation and fledging periods. Parasitized by Shiny Cowbird (Molothrus bonariensis).

VULNERABLE. Rare to uncommon, and very local. Somewhat more numerous locally, e.g. in NE Rio Grande do Sul (Brazil) and N of Pinamar in E Buenos Aires (Argentina), but in general now extremely scarce. Since 1850, this species’ population has undergone a catastrophic decline within its range of c. 120,000 km², this due mainly to drainage and agricultural conversion of natural grasslands, especially for livestock grazing; more recently, afforestation with non-native trees has begun to replace even more grasslands, especially rapidly in Entre Ríos and Corrientes (Argentina), where the species is still relatively common in recently burnt areas and has also been found in old paddyfields. Further threats are destruction of nests by fires and high levels of brood parasitism by Shiny Cowbird. Current stronghold possibly in SE Uruguay, with c. 1500–2200 individuals, mostly in Rocha; in Brazil common only near Arcos (Minas Gerais), in SE Santa Catarina and in NE & SE Rio Grande do Sul; in Argentina, decline especially marked in Buenos Aires, where previously common (and still is N of Pinamar), and most recent records from Corrientes and Entre Ríos. Occurs in Chaco, Mburucuyá and El Palmar National Parks, San Juan de Poriahú and Campos del Tuyú Private Reserves and Ribera Norte Municipal Reserve, all in Argentina, Aparados da Serra and São Joaquim National Parks, in Brazil, and Bañados del Este Biosphere Reserve and Laguna de Castillos, Potrerillo de Santa Teresa and Los Indios Reserves, all in Uruguay.