Macroecological patterns of resource use in resident and migratory hummingbirds

Hummingbirds (Family Trochilidae) are key pollinators in several biodiversity hotspots, including the California Floristic Province in North America. Relatively little is known about how hummingbird diets change throughout the year, especially with regard to how migratory hummingbirds affect resident hummingbirds at stopover sites. In this study, we examine how hummingbird species, migratory status, sex, geographic region and local plant diversity influence floral resource use before, during, and after an influx of migratory hummingbirds (primarily Rufous hummingbirds, Selasphorus rufus) across California. We expected distinct floral resource use based upon species’ migratory status (resident vs. migrant), sex, sampling period, and geographic region. We employed DNA metabarcoding to detect plant DNA in hummingbird fecal samples to analyze diet diversity, composition, overlap, and interaction networks. We found significant effects of sex, sampling period, and migratory status on the alpha and beta diversity of plant taxa present in fecal samples. Analyses of Anna's hummingbirds (Calypte anna) alone revealed that female fecal samples contained higher plant species richness. In addition to hummingbird-pollinated plants, fecal samples also contained non-ornithophilous plants and species of agricultural importance. Diet overlap and plant-pollinator network analyses revealed high overlap in plant taxa used between hummingbird species, and networks were more connected, less nested, and less specialized than null models. DNA metabarcoding is minimally invasive and provides a detailed view of hummingbird diet, permitting large-scale studies. Insights into hummingbird diets are especially valuable given the logistical difficulties of directly observing floral visitation and foraging across broad temporal and spatial scales.