Document Type
Article
Publication Date
5-8-2025
Publisher
BioOne / California Botanical Society
Abstract
There are 129 red-flowered species in western North America that fit the hummingbird pollination syndrome. Theory predicts that these flowers should produce a specific red color that is conspicuous to hummingbirds but not to bees. In a few well-studied cases, red flowers can be produced with pelargonidin, cyanidin, or both—sometimes complemented with the addition of yellow carotenoids and sometimes not. Which pigment combinations are most common in California and whether they affect conspicuousness to hummingbirds and bees remain unknown. To determine the taxonomic distribution of the pigments responsible for red hummingbird-pollinated flowers, we quantified the color of 36 red-flowered species with the hummingbird pollination syndrome, primarily native to California. Approximately 40% of the sampled species produce pelargonidin and carotenoids, 27% produce cyanidin with carotenoids, 25% produce pelargonidin without carotenoids, and the remaining 8% produce cyanidin without carotenoids. From a phylogenetic perspective, primary anthocyanidin type and the presence of carotenoids have evolved independently among these sampled red-flowered hummingbird species. The reflectance spectra from these four pigment categories are very similar (strongly absorbent in the ultraviolet and visible range up to ∼600 nm). Consequently, there are no significant differences in the conspicuousness among species in these four biochemical categories to hummingbirds, nor are they significantly different from one another from the perspective of bees. Chromatic contrast values were below the coarse detectability threshold for bees in 67% of species and the mean conspicuousness for bees, in all pigment categories, is also below this threshold. The average total anthocyanin concentration is approximately 2× higher in species without carotenoids in their flowers compared to those species with carotenoids suggesting there may be a trade-off between these two pigment categories in creating red flowers. It appears red hummingbird flowers in California utilize a range of types and amounts of pigments to converge on a relatively narrow, red adaptive peak in order to avoid detection by bees while remaining conspicuous to hummingbirds.
Recommended Citation
León-Osper, M., Rossi, V., Conrad, K., Mena, J. H., Meslow, E., Fuller, A., Narbona, E., & Whittall, J. B. (2025). California red hummingbird flowers: Color convergence across four biochemical categories. Madroño, 72(2), 68–95. https://doi.org/10.3120/0024-9637-72.2.a5
Comments
This is an open access article.