Temporal shift

 

Every spring, green and gold broad-tailed hummingbirds wing their way north from Central America to subalpine breeding sites in the western United States. The birds time their arrival to sync up with the showy emergence of glacier lilies, graceful flowers characterized by nodding, golden crowns of back-curved "petals." The flowers, which haunt the West's mountain meadows and streambanks, are one of the first to blossom after the snow melts and serve as key nectar banks for the hungry and amorous hummers.

But a recent study published in the current issue of the journal Ecology suggests that the Earth's warming climate is jeopardizing the bird and lily's temporal bond. According to the researchers, earlier snowmelt in the mountains (brought on by warming temperatures) has, in turn, led to a blooming shift in the lily, the first blossoms of which appear roughly 17 days earlier today than they did in the 1970's. Dwarf larkspur, another key nectar flower for the hummingbirds, blooms some 16 days earlier than it did in 1975, says David Inouye, a professor of biology at the University of Maryland and one of the study's co-authors.

The flowers, it seems, "are no longer synchronized with the arrival of broad-tailed hummingbirds, which depend on them for nectar. By the time the hummingbirds fly in, many of the flowers have withered away," taking their energy-rich nectar stores with them, reports the National Science Foundation, which funded the research.

The hummingbirds are changing their arrival times too, but not at the same rate, says Inouye. The broad-tailed hummingbirds are getting to the flowers five to six days earlier then they did in 1975. But biologists -- unsure how plastic the bird's migrating behavior is -- and are not convinced it can indefinitely adjust the seasonal timing of its nesting cycle to match the lily and larkspur's ahead-of-schedule flowering.

In twenty years, the hummingbirds will miss the first glacier lily flowers entirely if current trends continue, says the NSF. Given that the hummingbirds only lay two eggs per year and have life-spans of only two years, biologists are worried that the birds' and flowers' altered synchrony could lead the broad-tailed hummingbird to disappear from the Southern Rockies within just a few decades.

Inouye and his coauthors arrived at the results after analyzing years of phenological data -- information that relates seasonal biological events like spring flowering and species migration to climatic conditions -- from the Rocky Mountain Biological Laboratory (RMBL) in Gothic, Colorado. Since the mid '70s, RMBL researchers (including Inouye) and amateur naturalists have been keeping detailed records of when glacier lilies and broad-tailed hummingbirds (among other species) first appear at specific sites around the Laboratory.

Unlike other examples of climate change's disrupting effects at high altitudes/latitudes -- glacier melting or tree-line retreat, for example -- Inouye's work -- which focuses on two common species engaged in an accessible biological dilemma (one to which anybody who's ever rushed to the store for groceries only to find it closed can relate) -- is a particularly elegant example of the decoupling nature of climate change.

What's more, the study illustrates the "tremendous value" of keeping detailed phenological records; something anyone can do, Inouye says. The hummingbird study, for example, relied heavily on the decades-long observations of Billy Barr, RMBL's business manager. In other words, Inouye says, "You don't need a Ph.D. to make important contributions to climate change research."

He encourages people interested in keeping phenological records of species in their area to visit Nature's Notebook. This national plant and animal phenology observation program that seeks to involve the public in gathering data that scientists and policy makers can use to understand how species are responding to climate change and other environmental changes.

Marian Lyman Kirst is an editorial fellow at High Country News

Images courtesy of David Inouye, professor of biology at the University of Maryland and researcher at the Rocky Mountain Biological Laboratory

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