Diets of migratory rosy starlings (Passeriformes: Sturnidae) and their effects on grasshoppers: Implications for a biological agent for insect pests

Palaearctic-Oriental migrants Sturnus roseus are observed in large flocks in breeding areas and feed on insects, especially grasshoppers. However, the practical value of the long-distance migratory birds as a biocontrol agent remains unclear. We examined the diet of adult S. roseus and food items for nestlings in 2005 and 2006 and evaluated the role of S. roseus in reducing grasshopper abundance by bird-exclosure experiments from 2005 through 2007 in Yiche grassland, Xinjiang, China. Gizzard content analyses revealed that grasshoppers were the sole prey fed to nestlings by their parents. Orthopterans (93.8%, 93.7% in 2005 and 2006, respectively) predominated in the diet of adult S. roseus, followed by Coleoptera (3.1%, 2.9%) and Lepidoptera (2.2%, 2.5%). Use vs. availability analyses indicated that S. roseus tended opportunistically to take prey according to ranked availability. Grasshopper density showed significant differences between open and control plots during each of the four avian activity periods (spring arrival, breeding, postbreeding and fall migration) (P < 0.05) from 2005 till 2007. Average densities of grasshoppers in fall migration were 3.3, 3.6 and 3.0 times higher in bird exclosures than in open plots in 2005, 2006 and 2007, respectively. Our study demonstrates that the impact of S. roseus is sufficient to reduce grasshoppers to an acceptable level. Therefore, S. roseus might be encouraged to artificially increase population numbers so that they can function as a biological control agent for insect pests in breeding areas worldwide.