Endangered and invasive species meet in the desert Southwest

willow flycatcher
A southwestern willow flycatcher. Photo courtesy USGS.

New data to help inform tamarisk eradication and bird conservation efforts

Staff Report

New mapping by the U.S. Geological Survey may help resource managers in the southwestern U.S. figure out how they can bolster populations of the endangered southwestern willow flycatcher while at the same time trying to control an unwanted invasive plant that provides habitat for the tiny songbird.

The new report from the USGS provides detailed habitat information on the entire range of of the flycatcher, which breeds in lush, dense vegetation along rivers and streams from May through September. In 2013, the U.S. Fish and Wildlife Service designated 1,975 stream kilometers as critical flycatcher habitat, located in six states and 38 counties.

“The satellite model provides us with new capabilities to locate and monitor potential flycatcher habitat within individual watersheds and across its entire range” said James Hatten, Research Biogeographer with the USGS and the report’s author. “The satellite model also revealed how the quantity of flycatcher habitat is affected annually by drought conditions, with habitat declining in California from 2013 to 2015, while increasing in New Mexico and Texas.”

The mapping will also help show how the introduction of a non-native tree-killing beetle will affect flycatcher habitat. In 2001, federal biologists released tamarisk leaf beetles to try and control invasive tamarisk, an introduced plant that occurs adjacent to rivers and creeks. The tamarisk has aggressively replaced native vegetation communities and is also blamed for gulping up big quantities of water.

In the past 15 years the beetles have spread into the upper Colorado River Basin in southern Utah and Nevada, the main stem lower Colorado River in Arizona, and the Rio Grande in New Mexico. They pose a threat to flycatchers by defoliating tamarisk during nesting, exposing their young to increased temperatures and predation.

The USGS study found that beetles decreased flycatcher habitat 94 percent from 2010 to 2015 along the lower Virgin River, with only 6 percent remaining. The model also predicts that the beetle will destroy 36 percent of flycatcher habitat along the lower Colorado River and 55 percent along the upper Gila River in the next decade.

“We believe expanding this satellite model to the flycatcher’s range will help to improve the detection and evaluation of flycatcher habitat and territories,” said Greg Beatty, a Wildlife Biologist with the U.S. Fish and Wildlife Service.  “Also, using this technology to evaluate how leaf beetle may affect flycatchers and its habitat across its range is a tremendous step forward in our understanding, and may aid land managers across the Southwest.”

Government agencies and private organizations are trying to minimize beetle impacts on flycatcher habitat through a variety of activities, such as removal of tamarisk and replacement by native vegetation, and planting native plantations that were formerly agricultural fields. It is currently unknown how effective these actions will be in minimizing beetle impacts to flycatcher habitat, but the satellite model provides management agencies with a head start by identifying flycatcher habitat most at risk from the beetle.

“Reclamation developed a conservation program which includes the purchase of lands, and conservation easements along the lower San Pedro River,” said Carol Evans, a Wildlife Biologist with the Bureau of Reclamation. “This model partially fulfills Reclamation’s obligation to offset impacts to flycatcher habitat and assist all other land management agencies to track and predict changes in suitable flycatcher habitat over time. With the tamarisk leaf beetle module used in conjunction with the habitat model, it will give us some predictability of beetle movement and flycatcher response over time.”

The report, “A satellite model of Southwestern Willow Flycatcher (Empidonax traillii extimus) breeding habitat and a simulation of potential effects of tamarisk leaf beetles (Diorhabda spp.), southwestern United States,” is a USGS Open-File Report.

The study was a collaborative effort between the USGS, U.S. Fish and Wildlife Service, and U.S. Bureau of Reclamation.



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