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Hummingbirds Tracked During U.S. Southwest's "Second Spring" [Slide Show]

Monitoring hummingbird populations during the peak of fall migration in the Chiricahua Mountains helps scientists foresee how these primary pollinators of more than 150 U.S. flowering plant species respond to changes in climate
Rufous hummingbird



Patricia Despain

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Paradise, Ariz.—The Chiricahua Mountains here in far southeastern Arizona boast some of the most spectacular birding in the country; at no other time is this truer than in the early fall during the peak of hummingbird migration.

The tiny travelers, which play crucial roles in pollination and ecological stability, make their way down the Rocky Mountains to the Sierra Madres. They are attracted to a major seasonal change that happens on this borderland sky island during these months. A strong influx of moisture streams northward from the Pacific Ocean and the Gulf of Mexico bringing late summer heavy rains that have turned the sea of surrounding grasslands green. In the canyons, last year’s monster flames are becoming a distant memory: shades of red, pink and yellow dot the charred landscapes, signaling the return of wildflowers during this “second spring.”

The wildflowers offer the hummingbirds, mostly juveniles, an opportunity to indulge and fatten up on nectar before continuing on to Mexico or Central America for the winter. Birders and tourists come from around the world to observe hummingbirds here simply because of their beauty; however, few are aware of the integral function that hummingbirds serve for biodiversity in the region.

»View the Hummingbirds Slide Show

A single hummingbird may visit more than a thousand wildflowers a day. In the process, it picks up pollen grains and carries them from one plant to another, serving as the basis for cross-fertilization needed by the flowering plants to produce seed. Because hummingbirds—along with bees, butterflies and bats—act as primary pollinators for about 150 species of flowering plants in the United States (and more in Mexico and Central and South America), land managers and scientists want to keep a close eye on their numbers.

In the early morning hours of a recent fall day in Cave Creek Canyon at the Southwest Research Station, ecologist Susan Wethington led a group of citizen scientists and volunteers to monitor and record the migration. Based in Patagonia, Arizona, she is the co-founder and executive director of the Hummingbird Monitoring Network (HMN), a group devoted to maintaining hummingbird populations and their habitats. 

Group members received instruction on how to perform their roles. They set up their stations and, for the next five hours, each group member trapped and banded the birds, recorded data, and marveled at the animals in hopes of understanding a little more about the journey they’d made thus far.

Despite one's fascination with these fairy-like creatures, Wethington told the group, "There is still too little known about hummingbirds." Among the questions that need answers include: What does it take for hummingbirds to survive, reproduce and maintain thriving populations?

On this day alone, the group trapped and processed almost 100 birds—the busiest day this year—and they recorded seven species (in order of number): Black-chinned, Blue-throated, Magnificent, Rufous, Broad-tailed, Anna's and Calliope. The numbers are encouraging, Wethington says, a sign of recovery after the harsh conditions brought on by freezing temperatures, drought and wildfire of the past couple of years.

How hummingbirds will respond to climate change is a major concern, Wethington says. The Chiricahuas serve as an exceptional location for studying how well hummingbirds adapt. Here, four different ecological regions meet—the Rocky Mountains, the Sierra Mountains, and the Sonoran and Chihuahuan deserts—and serve as a biological crossroads of flora and fauna. In total, researchers have recorded 18 species in this canyon, more than in any other area north of Mexico.

The group's data from the peak of migration (for Anna's, Black-chinned, and Rufous hummingbirds) will be pooled with that of similar HMN groups working across the southeastern Arizona sky island region, California, Utah, Idaho, New Mexico, Colorado, British Columbia and Mexico City.

With the collected HMN data combined with remote sensing and other biological data, Wethington will work with a team of scientists led by ecologist Catherine Graham of Stony Brook University to study how the hummingbirds might adapt to the changing climate. A NASA grant supports the research as part of the agency's project to investigate how wildlife and ecosystems will respond to climate change.

With the Earth's rapidly changing climate, Wethington fears hummingbirds will face ever-greater challenges. In June, for example, biologists David Inouye and Amy McKinney of the University of Maryland and their colleagues reported in Ecology that glacier lilies were blooming earlier in the spring, at a time out of sync with the arrival of Broad-tailed hummingbirds traveling north.

"One of our biggest concerns is the changing phenology of the flowers that they visit to the timing of their arrival," Wethington says. Broad-tailed hummingbirds are expected to be among the most heavily affected species because they require high-mountain forest breeding sites to nest and raise their young.

So far, the Broad-tailed hummingbirds have proved resilient. Consider what they went through in the winter of 2010 to 2011, when freezing temperatures stretched as far south as Jalisco, Mexico. The following spring HMN researchers recorded a greater number of Broad-taileds at low- and mid-level elevations during migration. They noticed that the birds that made it through the cold survived by delaying their molting and changing the location of their stopover sites to lower elevations.

"The fact that they can do that is interesting," Wethington says.

Also interesting, she adds, is the role of fire as a land-management tool. Wildfire can be tragic to hummingbirds, as it is for any other species, but it can also help open up an area, return organic material to the soil, and stimulate the production of flowers—as it has this year—leading to rebounding populations.

Future projects are planned to help foresee how hummingbirds adapt to extreme weather patterns and to help inform conservation efforts, such as habitat restoration and enhancement, as well as public land management.

Wethington encourages more people to become involved. "It's a huge commitment. We wouldn't have ever gotten started without volunteers and citizen scientists."

»View the Hummingbirds Slide Show

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