Do plant secondary metabolites help drive avian granivore seed selection?

Plant secondary metabolites (PSMs), found virtually universally throughout the plant kingdom, function in myriad ways, including defense against enemies, attraction of pollinators, communication between plants, and protection against various abiotic stressors. Extensive research has examined how PSMs mediate interactions between plants and herbivores and plant and frugivores. In contrast, little research has investigated their potential role in defense against granivores. In two seed selection experiments, we quantified seed preference of house sparrows and native granivores, respectively, when offered each of 10 native seeds and proso millet, a commercial bird seed. House sparrows and native granivores greatly preferred millet over all offered native seeds. House sparrows largely rejected seeds of all five wildflower species, but native granivores preferred three of the five wildflowers. House sparrows readily consumed seeds of all five native grass species, but native granivores rejected Canada rye. House sparrows and native granivores both rejected seeds of Illinois bundle flower. Although seed preferences in the non-native house sparrow and native granivores differed significantly, we have found no consistent relationship between seed selection and presence or absence of classes of plant secondary metabolites.