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UA professor studies hummingbird migration

DNA, tracking data may help to understand population

A UA researcher is studying a species of hummingbird in order to better determine its migration patterns, hoping to discover how that may affect a decline in the rufous hummingbird population.

"Our perceptions of life may be vague due to the complexity of our study of the limitations of our senses," said William Calder, a University of Arizona ecology and evolutionary biology professor.

In order to explain the complexity of life, researchers often turn to the outside limits of biology. Calder said the hummingbirds' small bodies make them an "extreme" case.

"Many principles are clearer when we look at the extreme cases, which tend to exaggerate what goes on in moderate situations," Calder added.

Among these extremes, Calder said, are animals in high altitude or animals that live deep in the ocean.

"Other biological principles seen in the extreme are the smallest and the largest," Calder said, explaining the importance of his research on hummingbirds.

Between their breeding and winter habitats, rufous hummingbirds migrate farther than any other hummingbirds, Calder said.

He added that DNA evidence taken from feathers could affect the success of the birds' population by revealing an individual hummingbird's origins.

"The primary challenge to hummingbird survival is fueling high metabolism on a specialized diet," he said. "Preliminary data suggest that rufous hummingbird populations are declining, so we need to understand migration and its vulnerability."

In order to reach higher latitudes for summer breeding, some populations of rufous hummingbirds fly long migrations but stop along the way because they can't store enough energy for the entire flight.

"Too little is known about migration routes to determine where vulnerability to apparent (population) decline might occur," Calder said. "For example, declines in some (rufous hummingbird) populations could result from drought in stopover habitats."

In order to obtain this information, Calder has turned to mitochondrial evidence in order to trace the individual hummingbird's origins.

By supplementing limited information recovered from banding with additional mitochondrial DNA patterns, researchers can learn the geographic breeding regions of the birds, which may be the key to understanding population decline and eventually preventing it.

The banding of birds is a process of capturing and tracking animals that has long been used by researchers.

"Bird banding data are useful in both research and management projects," states the U.S. Geological Survey Web site. "Individual identification of birds makes possible studies of dispersal and migration, behavior and social structure, life span and survival rate, reproductive success and population growth."

By taking DNA samples of the rufous hummingbird population during breeding season, scientists can discover if the birds are local or have migrated.

Of particular interest to this study is the increasing appearance of rufous hummingbirds during the winter in the southeastern United States instead of Mexico, Calder said.

Study sites range between Jalisco and Sonora, Mexico, as well as much of the western United States and southern Canada, he said.

This research has a long-term collaboration, covered by Mexican permits, with the Instituto Manantlan de Ecologia y la Conservacio de Biodiversidad in Jalisco.