Molecular Quantification of Wild Birds’ Impact on Pests
We are using a novel technique called molecular scatology to document the diet of wild birds on organic farms. First, we collect feces from wild birds. Birds will be captured twice per year per farm for two years using a technique called mist netting (Fig. 1). After birds are captured, they are temporarily held in bags designed for safe handling until they defecate. We then collect body measurements, blood samples, and feathers for further analysis (Fig. 2). The birds are then released back into the wild. After the field season, the fecal samples are primed using a method called Polymerase Chain Reaction (PCR) with primers developed by Dr. Chaoyang Zhao and then sent to Dr. Erin Wilson Rankin at UC Riverside to use next-generation sequencing and checked against the GENBANK DNA-sequence database to determine what the birds were eating. Fecal sample analysis provides a snapshot of the diet of the birds. PhD student Joseph Taylor will also use a technique called stable isotope analysis on feather samples to assess how high on the food chain individual species are, as well as to examine feeding variability between individuals.
Characterization of Arthropods on Vegetation
PhD student Joseph Taylor is conducting extensive arthropod surveys on each farm twice per year for two years. He conducts visual counts (Fig. 3) on 10 broccoli and 10 kale plants per farm and can count up to six thousand aphids per plant! He also vacuums flying insects off plants using a D-VAC (Fig. 4). Finally, he collects insects using plastic cups called pitfall traps. In order to set these traps, he digs holes just big enough for the cups and buries the top level with the ground. All materials are washed and rinsed with ethanol between farms to avoid transfer of pathogens.
Bird Exclusion Experiments
We will be experimentally excluding birds from plants using bird-exclusion cages. Briefly, bird-exclusion cages will have 80 cm x 80 cm x 80 cm aluminum frames, covered on the top and sides with single-layer nylon bird netting; sham cages that allow bird access to crops have the same cage frame but not covered with bird netting. The bird netting is sufficiently fine to exclude birds, but sufficiently coarse to allow ready entry to insects, spiders, and other invertebrates; the cages are large enough to allow for normal crop growth and will be in place from transplanting until initial harvest. Cages will remain in place from transplant until harvest. At harvest, all arthropods will be collected using the insect-sampling methods described above, then plants will be harvested, scored for damage due to insects, and weighed. This will allow us to measure the sum impact of wild birds on pest insects, and benefits of this predation in reducing crop damage.