Behavioral responses to mammalian grazing expose insect herbivores to elevated risk of avian predation

Large mammalian herbivores (LMH) are important functional components and drivers of biodiversity and ecosystem functioning in grasslands. Yet their role in regulating food web dynamics and trophic cascades remains poorly understood. In the temperate grasslands of northern China, we explored whether and how grazing domestic cattle (Bos taurus) alter the predator-prey interactions between a dominant grasshopper (Euchorthippus unicolor) and its avian predator the Barn swallow (Hirundo rustica). Using two large manipulative field experiments we found that in the presence of cattle, grasshoppers increased their jumping frequency threefold, swallows increased their foraging visits to these fields six-fold, and grasshopper density was reduced by about 50%. By manipulatively controlling the grasshopper ability to jump, we showed that jumping enables grasshoppers to avoid being incidentally consumed or trampled by cattle. However, it increased their consumption rates by swallows 37 folds compared to grasshoppers that were unable to jump. Our findings illustrate how LMH can indirectly alter predator-prey interactions by affecting behavior of avian predators and herbivorous insects. The non-plant mediated effects of LMH on plant-dwelling arthropods in grazing ecosystems appears strong and common. We highlight that convoluted multispecies interactions may better explain how LMH control food-web dynamics in grasslands.