This species locomotes by walking, not hopping. The walking style has been described as similar to that of a quail (Jaramillo 2003, Cueto et al. 2013). It begins to sing at break of dawn and also begins foraging on the ground in the morning, and at midday is sometimes found in low shrubs to avoid the heat (Fjeldså and Krabbe 1990, Jaramillo 2011). Usually, the Common Diuca-Finch is seen in pairs or family groups as well as in small flocks during the winter non-breeding season (Jaramillo 2011).
No aggressive behavior has been witnessed, and Diuca diuca changes its seed preferences seasonally depending on other bird species’ presence, which seems to suggest that modifying their diet is less energy costly than aggressive behavior (Lopez-Calleja 1995).
Social and interspecific behavior
Usually, the Common Diuca-Finch is seen in pairs or family groups as well as in small flocks during the winter non-breeding season (Jaramillo 2011).
The Common Diuca-Finch’s egg to fledgling mortality rate is 68.3-82%, with 56.% of mortality occuring during the egg state (Lazo and Anabalón 1991, Marin 2011). An observational study of the Common Diuca-Finch’s nests frequently found missing eggs and chicks (Lazo and Anabalón 1991). In one instance Chimango Caracara (Milvago chimango) feathers were found in a nest that was missing two eggs. Other confirmed predators of the Common Diuca-Finch’s eggs and nestlings are the Austral Pygmy-Owl (Glaucidium nanum), mouse-opossums (Marmosa elegans), racerunners (Callopistes palluma), and the snake Philodryas chamissonis (Jiménez and Jaksić 1989, Lazo and Anabalón 1991). The brood parasite Shiny Cowbird (Molothrus bonariensis) also frequently punctures Common Diuca-Finch eggs, leading to mortality (Marin 2011). As high as 61% of Diuca diuca nests have been found to be parasitized by the Shiny Cowbird, and frequently found punctured eggs in nests are thought to be caused by this nest parasite (Johnson and Goodall 1967, King 1973, Marin 2011). Known parasites on nestlings include the subcutaneous larvae of a Philornis sp. (Diptera, Muscidae), which specialize on birds (Mezquida 2003). They are also known to be parasitized by the mite Harpyrhynchoides zumpti (Bochkov and Galloway 2001).