James W. Cornett

DESERT magazine

Imagine going to your neighborhood grocery store and discovering no food. Even worse, imagine every grocery store within a day’s drive was without food. What would you do?

For migrating hummingbirds, the grocery store is the ocotillo and the food is the nectar held within its blossoms. As the tiny birds arrive each spring, they are finding more and more ocotillos are not open for business.

The problem isn’t that ocotillos are not blooming. They are. It’s that some are blooming too soon, before the arrival of migrating hummingbirds. A warmer environment is the explanation, a phenomenon associated with changing climatic conditions first brought to the public’s attention in the early 1980s.

Hummingbirds matter. They are metabolic wonders that have already taught us much about animal and human physiology. Their renowned nightly torpor makes them unusual in the avian world. More importantly, their incredibly rapid wing beats and status as the smallest birds on our planet require they maintain unusually high metabolic rates, higher than any other group of vertebrates. Changes in the gas content of the atmosphere and patterns of plant growth that humans might not initially detect are more likely to impact hummingbirds first. Their fate, in effect, acts as an early warning system for significant changes in the environment.

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I first became aware of ocotillos and their special relationship with hummingbirds in early 2007. In that year, I initiated a long-term study on ocotillo ecology, in part, because there were dozens of ocotillos blooming in January – months before migrating hummingbirds would arrive in the Coachella Valley. When I returned home, I scanned the literature to see if January blooming was expected, or if it was something new. Not one of the books I checked indicated ocotillos regularly or even occasionally bloomed in January. California’s premier desert naturalist, the late Edmund Jaeger, wrote in 1969 in his Desert Wild Flowers that ocotillos bloomed in April and May, not in the dead of winter. The late botanist Philip Munz, in his A Flora of Southern California published in 1974, wrote that ocotillos bloom from March to July. As late as 2012, The Jepson Manual, the most authoritative publication on California plant life, repeated that ocotillos bloomed from March to July. Were all these texts wrong?

Ever since the pioneering work of ecologist John Grainger in the first half of the twentieth century, it has become well known that temperature can be an important factor determining when plants bloom. Grainger found numerous plant species in Britain flowered early each year when temperatures were higher than normal. In 1986, global warming and long-term climate change were specifically associated with early blooming of plants. Researchers Melvin Cannell and Rognvald Smith of the Institute of Terrestrial Ecology in Scotland demonstrated how several tree species were blooming up to 24 days earlier than they had in previous decades.

In 2007, Janice Bowers of the U.S. Geological Survey, brought the issue home to our own Sonoran Desert. She was one of the first scientists to provide evidence Sonoran Desert shrubs, including ocotillo, began blooming nearly 40 days earlier than they did a century ago. What’s more, her study suggested ocotillos and other shrubs ended their bloom more than a month earlier than in previous decades. This could be bad news for hummingbirds. In years of drought, the only reliable nectar-producing plant is the ocotillo and thus late-arriving hummingbirds would not find the energy source they need to complete their migratory journey. A late-season blooming collapse could be far reaching. The range of the ocotillo covers a band from west Texas to the Coachella Valley and so there would be disastrous consequences for most hummingbird species since all but one migrates through the Southwest and northern Mexico.

Already the numbers of our most beautiful Coachella Valley migrant, the rufous hummingbird, are in decline. We don’t know specifically how shifts in ocotillo blooming may be affecting the decline. What we do know is that rufous hummingbirds are frequently observed sipping nectar from ocotillo blossoms and, as mentioned above, the range of the ocotillo stretches across the entire width of the rufous’ north-south migratory route. And, once again, don’t forget the ocotillo is the only plant species that produces nectar in all years, even in years of severe drought.

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To get a handle on the effects of global warming on rufous and other hummingbirds, we need hard data on the blooming patterns of the ocotillo and the timing of migration of all species of hummingbirds. This is crucial to the fate of hummingbirds, the plants they pollinate and, most broadly, our understanding of environmental change. This is where desert residents and visitors can play an invaluable role. By collecting information on when ocotillos first bloom and the first and last date of migrating hummingbirds, an accurate and comprehensive understanding of one facet of environmental change can be obtained. This, in combination with other monitoring programs, will help us better understand changes in our environment and the actions we can take to maintain healthy hummingbird populations and, more importantly, healthy ecosystems.

If you would like to participate in this study, feel free to e-mail Jim Cornett at jwcornett@aol.com.