The studies are focused on low-elevation riparian habitat because roughly 75 percent of Utah's bird population depends on riparian habitat and 85 percent of the state's bird biomass is found in riparian areas.

Less than 2 percent of the state lands, however, is classified riparian.

The declining bird population is, of course, a concern.

And, as Norvell said, "To be honest, we don't know why. We've seen a large increase in disturbances ... mainly with respect to invasive weed species.

"We thought we'd see declines over time ... what we're seeing is a relatively steady decline. We haven't focused on one individual species, but we're sure there are some in the mix that are declining faster than others."

Studies, including Utah's ongoing songbird project, the Great Backyard Bird Count, counts by the Audubon Society and the Breeding Bird Survey conducted by the U.S. Geological Survey, hope to find both reasons and solutions.

Utah's study involves setting up mist nets below the canopy, roughly 10 feet off the ground between trees. The nets are 12 meters long and 2 meters high and so thin they are almost impossible to see.

Small birds fly into the nets and are gently removed, where they are identified by species, examined for feather wear, sex, breeding condition and age, and are then banded and released.

"We're just trying to see how long birds live, what percentage of birds survive year to year, numbers and kinds of species and number of individual birds," said Sonia Schmieder, who leads the Utah Project for the DWR.

On one particular day, 49 birds were caught in a net set below Jordanelle Dam — 30 of those were new catches and 19 were recaptured birds, one that had been banded in 2003.

Over the years, at the Jordanelle site, as many as 1,300 birds have been banded on a single day and as few as 245. Since 1994, at all locations, more than 30,000 birds have been identified and banded.

Most of the birds banded this year have been the yellow warbler, warbling vireo, song sparrow and cedar waxwing. Utah holds the record for the oldest bird banded — a warbling vireo that was 14 years old.

Because birds are tied to the area they were born, "and when we see juveniles not coming back, we make the general assumption that they did not survive the year," said Norvell.

"We don't know if it's migration habitat or if it's breeding habitat where juveniles are not sturdy enough to make it through the year. If it's migration habitat, then there may not be enough good stepping stones for them to get all the way south for the winter. If it's wintering habitat, then that becomes an issue. These are all questions we have and would like answered."

At this point, he said the DWR has excellent data on 17 species and hopes are, with help from other groups and states, to expand the list.

What is known is that studies in Utah and elsewhere show the songbird population is on a steady decline, and work is under way to discover why.