Molecular scatology and high-throughput sequencing reveal predominately herbivorous insects in the diets of adult and nestling Western Bluebirds (Sialia mexicana) in California vineyards | La escatología molecular y la secuenciación de alto rendimiento revelan el predominio de insectos herbívoros en las dietas de adultos y polluelos de Sialia mexicana en los viñedos de California
2017
Jedlicka, Julie A. | Vo, Anh-Thu E. | Almeida, Rodrigo P. P.
Determining the ecosystem function of high-order predators is critical for evaluation of food web interactions. Insectivorous birds are abundant predators in many ecosystems yet because they forage upon small taxa, it remains largely unknown whether birds are providing ecosystem services in the form of pest control or disservices by preying upon predaceous arthropod species. We extracted DNA from noninvasive fecal samples of adult and nestling Western Bluebirds (Sialia mexicana) in California vineyards. Using universal arthropod-specific primers, we sequenced prey items via massively parallel sequencing on the Illumina MiSeq platform. Bluebirds consumed a broad diet comprising 66 unique arthropod species from 6 orders and 28 families. Aedes sp. (mosquitoes: Culicidae), a previously unknown prey, was the most common item recovered, occurring in 49.5% of the fecal samples. Ectoparasitic bird blowfly (Protocalliphora) DNA was found in 7% of adult and 11% of nestling samples, presenting clear evidence of active feeding by the avian hosts on adult or larval ectoparasites. Herbivorous insects, primarily from the orders Hemiptera and Lepidoptera, represented over half (56%) of the prey items in bluebird diets. Intraguild predation (consumption of predator or parasitoid arthropods) represented only 3% of adult and nestling dietary items. Diets of adults were significantly different from nestlings as were diets from birds sampled in different vineyard blocks. Sex, date, number of young, and individual bird (based on resampled individuals) were all insignificant factors that did not explain diet variability. Nestling age was a significant factor in explaining a small amount of the variability in dietary components. In addition, our analysis of subsampling larger fecal samples and processing them independently revealed highly dissimilar results in all 10 trials and we recommend avoiding this common methodology. Molecular scatology offers powerfully informative techniques that can reveal the ecosystem function and services provided by abundant yet cryptic avian foragers.
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