Research Disproves Majority
Of Willow Flycatcher Notions

ALBUQUERQUE — The Southwest willow flycatcher should perhaps be renamed the box elder bee catcher.

Scott Stoleson with the Rocky Mountain Research Station here says little is known about this small songbird that was listed as an "endangered" species in 1995. The conventional wisdom is based on what people think they know about it, but Stoleson's research is showing a new picture of the bird.

"The willow flycatcher is a drab little bird that has caused a great deal of controversy in the Southwest," Stoleson says. "It lives in riparian areas."

The birds establish territories within these areas.

"Some territories are single males," he says. "Some ‘territories’ don't include any birds at all."

The bird occurs in about 209 sites throughout the Southwest.

"This is optimistic," Stoleson says, "because 56 of these 209 sites didn't have any birds in them in the year 2000."

Most populations are small where they are found.

"Over 33 percent of these 209 sites have five or fewer territories," he says. "There's really not a lot of these little suckers around."

Recent genetic work indicates that some areas thought to be populated by willow flycatchers are actually populated by another similar bird.

The two populations in the White Mountains of Arizona have disappeared altogether.

Because it's a rare species, Stoleson says, there was a lack of information about the willow flycatcher, especially when it was first listed.

"A lot of research has been done in the last five years," Stoleson says.

A lot of the information has been extrapolated from other sub-species which have been studied more.

"There are other sub-species all through North America and in the East that are actually increasing," Stoleson says, "but these cover different ecosystems."

Information from the Southwest, he says, mostly comes from degraded or altered riparian systems.

"The largest population in Arizona comes from a salt cedar monoculture at Roosevelt Lake," Stoleson says. "Most populations in the southwest are intensively managed, usually through cowbird traffic."

Consequently, he says, a lot of the information coming from the Southwest doesn't say how a healthy population functions.

The southwestern willow flycatcher is a neo-tropical migrant. Fecal samples indicate that they are general insectivores.

"They eat a variety of flying, crawling, hopping insects," Stoleson says, "not just flies."

The birds leave in August or early September. They spend six or seven months in winter territories in Central America, mostly on the Pacific slope.

According to conventional wisdom, Stoleson says, habitat loss and degradation is threatening the bird. This habitat loss is due to a number of factors that supposedly includes urban and agricultural development, water management, livestock grazing, invasion by exotic plants, especially salt cedar in riparian areas, and cowbird parasitism.

The cowbird is also a native, neo-tropical migrant bird.

"They have an interesting reproductive strategy," Stoleson says. "What they do is lay their eggs in the nests of other birds. The eggs hatch faster than the host bird's, and the host bird raises the cowbird."

There is a lot of conventional wisdom based partly on these other sub-species and partly on a lot of other things, Stoleson says.

The willow flycatcher is thought to prefer willows. They require water, but they cannot tolerate brood paracitism.

Grazing is necessarily detrimental to the species, according to the conventional wisdom.

At the U Bar Ranch in southwestern New Mexico, where Stoleson has studied the willow flycatcher, the birds flycatchers can be found in tall, mature riparian areas along the Gila River among cottonwoods that are 140 feet tall.

Stoleson says they found more than 80 species of breeding birds in the riparian woodlands on the U Bar Ranch.

"Southwestern riparian areas are renowned for their high bird densities," Stoleson says. "Because of the accessibility of water and high sunshine, there's a lot of vegetative production. That means a lot of bugs, and that means a lot of birds."

The highest published densities of breeding birds in North America are in two areas in Arizona. Stoleson says his research indicates there are more at the U Bar.

"This area has been grazed by cattle since the 1880s," Stoleson notes. "The bulk of the Gila Valley is the U Bar Ranch. That's where we've done most of our research. It's a working cattle operation."

The Rocky Mountain Research Station has been involved in studying the southwestern willow flycatcher since about 1997.

"This was actually a collaborative project," Stoleson says. "It's important to emphasize that. There's us, there's Western New Mexico University, there's the Gila National Forest, there's the U Bar Ranch, Phelps-Dodge, which owned the land of the U Bar Ranch, and then other private landowners including the Nature Conservancy."

They looked at how many willow flycatchers are in the Gila Valley, how are they doing, what habitat they are using and how the management practices on the U Bar, specifically grazing, affected the willow flycatchers.

Starting in 1994, the populations increased dramatically, but a drouth that reached all the way down to Costa Rica soon caused a drop in numbers.

"It started recovering this year," Stoleson says.

This year, there were about 618 nests in total in the study area.

"We don't know exactly what happened to some of those nests," Stoleson says.

He notes that about 49 percent of the nests that were checked were fresh.

"For a small songbird, that is about average," Stoleson says. "It's pretty good."

About 18 percent of them had been parasitized.

"That's based on a small sample, because we're not really sure about the nests that were really high," Stoleson says.

The highest rates of parasitism were in the years that the populations were increasing dramatically.

"So the conventional wisdom that brood parasitism was necessarily bad doesn't hold water," Stoleson says.

Habitat can be considered in multi-spatial scales that include tree, space around the nest or whole patches of riparian area.

Thirty percent of the 14,000 trees they counted were box elders, which accounted for more than 75 percent of the nests.

"Statistically, that's way out of whack," Stoleson says. "I interpret that to mean preference."

Almost 40 percent of the trees in the study area were willow.

"Less than 12 percent of the nests are in willows," Stoleson says. "Statistically, that's way out of whack. I interpret that as avoidance."

Generally, Stoleson says they found the greatest concentration of nests in areas with good canopy cover, close to water, with more box elder, more shrubs and more trees.

Flycatcher presence was most related to the presence of box elder and uniformity of shrub densities.

Willow flycatcher habitat is box elder, Stoleson contends.

"What about the conventional wisdom that willow flycatchers need or prefer willows?" Stoleson asks. "We compared the number of willow stems around the nests with willow stems at random points, and there was no difference."

They weren't picking areas that were more willowy than others.

Conventional wisdom also holds that willow flycatchers are closely associated with water.

"We measured distances to the nearest open water," Stoleson says. "They are actually closer to water. This conventional wisdom is true."

The biggest issue, however, was how grazing at the U Bar Ranch affected willow flycatchers.

"That's a problematic thing," Stoleson says. "It's something the recovery team struggled with because there are problems with studies of grazing impacts on wildlife, especially birds."

There are few studies in number, he explains.

"Those in particular in the Southwest are very few in number," Stoleson says.

Those that do pertain to the Southwest tend to have a lack of "controls". They also tend to be poorly defined.

"That means that people are measuring things that aren't all that meaningful," Stoleson continues. "A lot of these studies really aren't very useful."

The U Bar, however, had riparian areas that had been grazed and other riparian areas that had been fenced off and not grazed.

Some of the patches that were grazed were grazed seasonally; others were grazed year around.

"Over half of the excluded patches had willow flycatchers," Stoleson says, "but almost 90 percent of the grazed patches had flycatchers."

The grazed patches had significantly more flycatchers per acre than the patches where grazing had been excluded.

"Grazing, as it's practiced on the U Bar Ranch — and that's a key phrase — has no negative impacts that we could detect on occupancy, density, nest success or brood paracitism," Stoleson says.

He says he's been asked if grazing might be beneficial to willow flycatchers, but he says that's too vague a question to answer.

Grazing management varies widely. It most likely depends upon individual sites and individual range management practices.

He thinks both livestock and endangered species can benefit from sound management.

The U Bar supports the largest and perhaps healthiest populations of southwestern willow flycatchers.

Stoleson also found that willow flycatchers eat a lot of bees and wasps, a lot of bugs and beetles and some flies and gnats.

"When you look at what's out there," Stoleson says, "they are eating a disproportionate amount of bees and wasps, bugs."

They eat relatively few flies compared to the number of flies that are in the habitat Stoleson studied.

"This suggests that willow flycatchers may not be general insectivores as the general wisdom suggests," Stoleson says. "They may specialize to some degree in bees and wasps."

But he says more research is needed to confirm this.

The research gathered over the last five years presents something of a different picture of the willow flycatcher than conventional wisdom would suggest. Indeed, the research suggests the bird is adaptable, but it also suggests that more research should be done.

"The U Bar is good for willow flycatchers, but then so is Roosevelt Lake in Arizona," Stoleson says.