Effects of nutritional and anti-nutritional properties of seeds on the feeding ecology of seed-eating birds of the Monte desert, Argentina

JUAN MANUEL RÍOS; ANTONIO MANGIONE; LUIS MARONE

THE CONDOR

COOPER ORNITHOLOGICAL SOC

Lugar: California; Año: 2012 vol. 114 p. 44 - 55

0010-5422

Food quality and physiological capacities and limitations of animals to recognize and process food are among the factors influencing feeding choices of desert birds. Seed-eating birds of the central Monte desert generally select to feed on grass seeds rather than forb seeds. We studied some of the mechanisms underlying seed selection patterns in seed-eating birds of the Monte desert. We analysed nutrients and secondary compounds of the 15 most abundant seeds in the soil seed bank and their relationship with the field diet of six seed-eating bird species. Results indicated that grass seeds contained more starch and less total phenols than forb seeds and are free from alkaloids. The field diet of the most graminivorous birds was correlated with seed starch concentration, while generalist diet was correlated with seed abundance. To assess the plausible mechanisms underlying seed selection by birds, we performed feeding trials with three species which differ in their diet breadth: a generalist (Rufous-collared Sparrow [Zonotrichia capensis]) and two graminivorous (Many-colored Chaco-Finch [Saltatricula multicolor] and Common Diuca-Finch [Diuca diuca]). We postulated that (1) the level of starch and (2) the presence of phenolic compounds and alkaloids influence food preference. Results suggest that the most graminivorous birds preferred high starch diets and avoid diets with phenolic and alkaloids. Instead, the generalist species foraged regardless of starch content and its food intake was reduced only by some of the phenols and alkaloids tested. Seed chemistry could explain some important features of seed selection by birds in the Monte desert.