The hummingbird-red flower connection

Is the long-held idea that hummingbirds prefer red, tubular flowers true? PhD candidate Patrick McKenzie (Robin Hopkins, Advisor) was featured in an episode of the podcast, A Way to Garden to discuss his findings that the  migratory nature of ruby-throated hummingbirds drive the phenomenon.

The scale required to track flowering times and hummingbird movement across the Eastern seaboard is not possible with traditional fieldwork. McKenzie's solution was to use the community science platform iNaturalist, which holds millions of observations submitted by people.  In a study published in Current Biology, Mckenzie assembled a dataset of approximately 1.7 million observations using AI to label the color of the flower in each posted image as red, blue, green, or yellow.

The study found that for all flower colors except red and orange, blooming advanced northward at a consistent rate through spring — starting in the South early in the year and reaching the Northeast by May and June. The meant that in the month before hummingbirds migrated north — march and April — there were no red or orange flowers blooming the Eastern U.S. However, once the ruby-throated hummingbirds arrived, red and orange flowers appeared, a near-perfect geographic and timing correlation.

The study is the first to document this color-based seasonal lag. On the West Coast, where Anna's hummingbirds are present year-round (not migratory), this same pattern does not appear. The findings suggest this co-evolutionary relationship between red/orange flowering plants and ruby-throated hummingbirds was built over millions of years, with the flowers blooming having evolved to coincide with hummingbird arrival, ensuring successful pollination.