Although normally active during the day, the male may sing at night during the breeding season, as he tries to attract females and defend his territory. When singing, the male chooses a prominent spot, points his beak vertically and ruffles his feathers. He will also fight with and chase away other males. Whilst thought to be mainly socially monogamous, marsh seedeaters are known to mate promiscuously when the population is at high density. Once laying has taken place, pairs remain faithful; the female incubates the eggs alone, but the male joins her in feeding and caring for the nestlings (3).
The marsh seedeater balances on tall grasses to pick seeds from the seed heads, and consumes no other food (3).