In North America laying begins from late May to early June. The nest is globular, with side entrance, build with dry grasses and sedges and lined with fine grasses, hair, feathers and plant down. The male build the outside layer of the nest, but is finished by the female who adds the lining. Females begin laying between three and seven days after the nest is finished. Eggs are laid daily until the clutch is complete. The eggs are white and unmarked, with a smooth and glossy surface texture (Baicich and Harrison 1997). In North America, only one record of brood parasitism by Brown-headed cowbird (Molothrus ater) has been reported (Herkert et al. 2001). Only the female develops a brood patch and she is solely in charge of incubation and brooding the nestlings. Mate feeding by the male has not been reported and is unlikely due to the small contribution of males to parental care. Hatching seems to be asynchronous but variation along the breeding season and between populations is expected. Nestlings hatch naked with eyes closed with an average body mass of 1.34 g (Crawford 1977). In North America, both sexes feed the nestlings but males feed at very low frequency. Fecal sacs are removed from the nest by adults. Life-history traits are likely to vary between North and South America. In North America, clutch size range from 4-8 eggs, incubation is 12-14 days and nestlings leave the nest after 12-14 days.