We assessed seed preference in four species of sparrows that are common to the central Monte desert of Argentina. Our hypotheses are that (1) sparrows always prefer grass over forb seeds and (2) different species of sparrows show the same preferences when consuming seeds. We presented seeds from eight species of plants (four grasses and four forbs) in both choice and nonchoice experiments. In general, sparrow species preferred grass over forb seeds, though one of them (Rufous-collared Sparrow [Zonotrichia capensis]) included one forb species (Parthenium hysterophorus) among its preferred seed items. Among grass seeds, sparrows avoided or showed less preference for the tiny seeds of Sporobolus cryptandrus, which suggests that seed weight may affect seed choice among grasses. Avoidance of most forb species, by contrast, could not be associated with seed size, probably because of the presence of unpalatable or toxic compounds in forb seeds. Experimental evidence suggests that the main feeding pressure of sparrows is clearly directed to grass seeds, which coincides with reported information on bird diet. Results support assertions that sparrows can cause a negative effect on the composition and abundance of grass seeds in the soil seed-bank, a necessary condition for birds in playing a significant role on grass population dynamics in the central Monte desert of Argentina.
Preferencias por Semillas de los Emberízidos del Desierto del Monte, Argentina: Implicancias para la Interacción Semillas-granívoros