Straight-billed Reedhaunter

This bird is found in north-eastern Argentina, south-eastern Brazil and Uruguay. In its range, it is essentially limited to marshy areas in pampas and campos from coastal lowlands to highlands. In Brazil, it is found in Rio Grande do Sul and Santa Catarina States. In Argentina, it occurs in Entre Ríos and the extreme north-east of Buenos Aires Provinces. In Uruguay, it is limited to the eastern and southern part of the country. In recent years, it has been recorded in Cerro Largo, Canelones, Maldonado – where Charles Darwin found it in 1833 at Laguna José Ignacio and Laguna del Diario, where it can still be found –, Rocha, San José and Treinta y Tres Departments (especially at the Quebrada de los Cuervos). From Lavalleja Department, there are only records from 1994, but the bird probably is still found there. This species prefers marshy and swampy areas between sea level and 1,100 m ASL. A key feature of prime habitat is an abundant growth of caraguata (spiny eryngos, Eryngium spp.), such as E. pandanifolium which it utilizes particularly in upland localities. It is sometimes claimed that the two reedhaunters differ in microhabitat preference, occurring sympatrically in the same region but not within the same locality, but this seems to be incorrect.

As with many of its relatives, rather little is known about its reproductive habits. In southern Uruguay, a juvenile was observed in mid-January (i.e. midsummer).