Hummingbirds are important pollinators in temperate and tropical ecosystems in the Americas, especially in biodiversity hotspots like the California Floristic Province (CFP). Despite this, relatively little is known about the diet of hummingbirds in the CFP, beyond opportunistic observations at specific plants or studies that are limited in scope to small geographic areas. It has long been assumed that the majority of hummingbirds are specialists that feed predominantly upon plant species that present narrow, tubular flower corollas. While hummingbirds often, though not always, prefer flowers with tubular corollas in both field and choice experiments, analysis of hummingbird diet on larger geographic and temporal scales, such as that of the CFP, has not been undertaken. To address this question, we coupled foraging observations with next-generation sequencing of hummingbird fecal samples at multiple sites and seasons within the CFP.
We found evidence that hummingbirds in the California Floristic Province have a surprisingly wide diet niche, and do not feed exclusively on flowers with tubular corollas. Pollination networks constructed from the diet data suggest shifts in network structure in terms of both the identity and number of linkages of hummingbird pollinators in the CFP. We also found several distinct orders of insects and arachnids in hummingbird diet and significant differences in diet composition based on hummingbird species, sex, location, and time of year. This observed diet plasticity is likely due to flowering phenology, sex-specific demands of reproduction, the potential for competition with migratory hummingbird species during peak migration season in the early spring and mid-summer to early fall in the CFP. Further study on the diet of these important pollinators will be crucial to understanding local and regional patterns of plant-pollinator interactions, and the potential impact of stressors such as climate change, pathogens, and the influx of migratory pollinators.