Seed preferences in sparrow species of the Monte desert, Argentina: implications for seed-granivore interactions

V. R. CUETO; L. MARONE; J. LOPEZ DE CASENAVE

AUK

The American Ornithologists' Union

Año: 2006 vol. 123 p. 358 - 367

0004-8038

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) diff erent 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 aff ect 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 eff ect on the composition and abundance of grass seeds in the soil seed-bank, a necessary condition for birds in playing a signifi cant role on grass population dynamics in the central Monte desert of Argentina.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 aff ect 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 eff ect on the composition and abundance of grass seeds in the soil seed-bank, a necessary condition for birds in playing a signifi cant role on grass population dynamics in the central Monte desert of Argentina.