The bluebird rests in a valley oak after flying above the grass, hovering, hunting for insects. Lace lichen covers the oak’s branches. Western bluebirds eat mainly ground-dwelling insects in summer, adding fruits and seeds in winter. This image was captured on February 1, 2010 at Stanford's Jasper Ridge Biological Preserve. These birds were flying down into the grass, foraging for food. This one is perched in the Valley Oak near the Visitor Parking Lot. February 1, 2010 at 10:50 am. Stanford’s Jasper Ridge Biological Preserve is a 1,200-acre biological field station and preserve whose mission is to contribute to the understanding of the Earth’s natural systems through research, education, and protection of the Preserve’s resources.Guided tours are offered to the Stanford community and the public. Funds from this notecard project benefit Jasper Ridge Biological Preserve. Special thanks to John Working for encouragement and financial support.