Secret Sex Lives of High-Nesting Finches Uncovered In Rockies

James Owen
for National Geographic News
August 24, 2004
Mountain accidents are an occupational hazard for University of Wyoming researchers on the trail of the rosy-finch, North America's highest breeding birds.

The risks the researchers face were highlighted last month when one of David McDonald's graduate students fell during a climb. She was trying to reach a rosy-finch nest perched at more than 10,000 feet (3,050 meters) in the Snowy Range of the Rocky Mountains.

Paramedics had to be called to provide a medevac for the student, who has asked not to be identified for this story. "It's a testament to her youth and resilience that she seems to be mending well," said McDonald, a zoology professor at the University of Wyoming, Laramie. "She feels that, for the moment, lab genetic analyses are as extreme as she wants to be."

The nest proved to be the first nest of a brown-capped rosy-finch recorded in Wyoming.

It marks the latest breakthrough for McDonald and his team in their efforts to map the nesting sites and understand the breeding behavior of these poorly studied birds.

Currently, there are thought to be three species of rosy-finch in North America (though McDonald says even this isn't known for certain). These are the brown-capped, found almost exclusively in Colorado; the black, which ranges from New Mexico to Montana; and the gray-crowned, the most widespread variety, which breeds as far north as Alaska.

All three have characteristic pale rosy markings on their undersides and wings. The problem for researchers is that rosy-finches are the highest breeding birds in North America. "They are also the highest breeding vertebrate in the lower 48 [U.S. states]," McDonald said. "I suspect they rarely nest below 11,000 feet [3,350 meters] in Colorado and 10,000 feet [3,050 meters] in Wyoming."

Tough Birds

Describing them as "tough, resilient birds," McDonald says rosy-finches breed at such unforgiving altitudes to escape predators and competitors.

"If you're tough enough, the rocky crags and alpine meadows provide abundant seed and insect resources, as well as cracks that hugely decrease vulnerability to predation. The steep cliffs eliminate accessibility for mammals," McDonald said.

In 2002 another University of Wyoming graduate student, Maureen Ryan, discovered only the fourth nest of a black rosy-finch ever recorded. This was in Utah's Uinta Mountains.

The nest was found while field-testing geographic information systems (GIS) equipment as a method to locate these birds. The nest contained a clutch of five eggs, opening up a new avenue of research.

"Once we realized we could get at some parentage data, that was clearly the priority," Ryan said.

She took blood samples from both the nestlings and the male parent.

Using microsatellite DNA fingerprinting—a method used to determine paternity in animals—researchers determined that the samples suggested the female had been visiting neighboring males for sneaky copulations.

This behavior was supported by samples later taken from other black rosy-finch nests, with around 25 percent of chicks sired by males other than the female's nesting mate. For the first time this bracketed female rosy-finches with a range of other birds, from flamingoes to sparrows, that also "play" away from home.

"Let me point you to thousands of scientific papers on the subject," McDonald joked, before offering some possible reasons for this behavior: avoiding harassment, provisioning for nestlings, increasing genetic diversity in offspring, boosting the chances of successful egg fertilization.

Multiple Mates

The team's findings raise the possibility that in the two other species of rosy-finch females mate with multiple males.

Through their DNA studies, the researchers also hope to resolve the question of whether or not the three birds really are separate species.

Some scientists have suggested they all belong to one species, while McDonald says at least five forms are easily distinguishable in the field.

If three species are confirmed, McDonald says this could have significant implications for the futures of at least two of them, particularly in light of the looming threat from global warming.

"The black and brown-capped have fairly small global ranges," he said. "The brown-capped, in particular, is essentially restricted to the Colorado Rockies. Because it is the most southerly form, global warming could push it up to the point that its total habitat would be greatly diminished.

"Add other insults such as intense UV [ultraviolet light] and you might have a recipe for endangerment." (Increased UV due to a thinning ozone layer, caused by human-made chlorofluorocarbons in the atmosphere, has been implicated in declines and malformations in amphibians.)

With summer soon to mellow into fall, further mountain forays by McDonald and his team will have to wait until next year.

Meantime, the latest generation of rosy-finches, many with dubious paternity, will be descending from their snowcapped nurseries before winter sweeps in once again.

The University of Wyoming's rosy-finch research is supported by funding from the National Geographic Society and the National Science Foundation.

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