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July 18, 2013

Male broad-tailed hummingbird in researcher's hand

A male broad-tailed hummingbird (Selasphorus platycercus) rests briefly in a researcher's hand at the Rocky Mountain Biological Laboratory. The dusting of yellow pollen at the base of its bill may have come from a glacier lily flower (Erythronoium grandiflorum), the first of the wildflowers to bloom in the spring when migratory birds arrive from their winter homes in Mexico.

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The glacier lily flowers are flowering earlier as the climate warms, with a record early flowering in 2012. Flowering now begins before the hummingbirds arrive.

In a research study funded by the National Science Foundation's Division of Environmental Biology (grant DEB 0922080), David Inouye and Amy McKinney of the University of Maryland and colleagues found that the lilies are blooming some 17 days earlier than they did in the 1970s. This means that their blooming is no longer in synch with the arrival of the hummingbirds that rely on the nectar. By the time the hummingbirds arrive, many of the flowers have withered away along with their nectar-filled blooms.

Each spring, the broad-tailed hummingbirds fly north from Central America to the Western U.S. Here in these high-mountain breeding grounds they will raise their young over the short mountain summer. Males actually arrive before the flowers bloom to scout for territory.

But, says Inouye and McKinney, the time between the arrival of the first hummingbird and the first bloom has collapsed by 13 days over the past four decades. "In some years," says McKinney, "the lilies have already bloomed by the time the first hummingbird lands."

Broad-tailed hummingbirds that breed farther south in states like Arizona, however, are less affected. Inouye says there is no obvious narrowing of the timing between the first arriving males and the first blooms of their favored flowering plant, the nectar-containing Indian paintbrush.

Global warming is happening faster in the higher latitudes, making these areas more likely to get out of sync ecologically. At the rate things are going, if the snowmelt continues to occur earlier in the spring, bringing earlier flowering, then the mountains will bloom with lilies long before the hummingbirds can finish their migratory journey north. (Date of Image: Unknown)

Credit: Photo by David W. Inouye

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