A Merry Chase for Willow Flycatchers
Cached deep in the heart of the Chihuahuan Desert lies a true oasis that shelters at least 170 bird species among its dense thickets of native cottonwood, seep willow, Gooding’s and coyote willow. The Gila Lower Box, located about 20 parched desert miles northwest of Lordsburg, boasts one of the highest bird diversities in New Mexico and is a significant breeding ground for the elusive Southwestern willow flycatcher (Empidonax traillii extimus), one of the four recognized subspecies of the Willow Flycatcher. The bird’s state and federal endangered status has garnered near movie-star status for the flycatcher, despite its tiny size and drab coloring. Last year, field biologists with the New Mexico State Land Office began to survey flycatcher populations in the Gila Lower Box.
“The BLM (Bureau of Land Management) biologists have been doing surveys for years, but there was a gap in their data where state land is located,” said Shawn Knox, assistant director of Field Operations for the State Land Office. Most of the Gila Lower Box is managed by the BLM except for a one-mile stretch of the river that crosses state trust land.
In that stretch, biologists Knox, Clay Bowers, and Mark Meyers stalked the tiny bird armed with two-way radios, tape players, binoculars and field notebooks during this year’s first survey in mid-May. Willow flycatchers are extremely difficult to distinguish except by their distinctive buzzy fitz-bew and, by only the most experienced surveyors, their whit, britt,andwheeoo calls. Heard amid the cacophony of morning bird song along the river, from cooing doves to squawking ravens and the twitters and trills of countless songbird species, survey work requires intense focus aided by portable tape players to broadcast the flycatcher’s signature calls.
Those calls serve to locate and identify the presence of willow flycatchers. The diminutive birds are close to invisible, their drab coloring blending into the dense understory of their habitat. The broadcast calls literally bring them out of the woodwork to defend their territory against other intruding flycatchers. By locating the birds during at least three separate periods throughout the breeding season, biologists can distinguish migrants from those that likely are nesting within the surveyed area Only the Southwestern subspecies breeds in the area, while other subspecies can be found during migration.
“That’s a super-aggressive male; he came right in,” said Bowers, watching a flycatcher zip close in response to a taped
fitz-bew call. The biologists worked both sides of the river and communicated via radio to assure they were not counting the same bird twice. The team slowly made its way upriver, slogging through snarled branches and leaf litter, and sidestepping jutting cliffs by wading into ankle-deep water. They infiltrated tangled vegetation to listen and play the recorded calls where the birds are most likely to respond.
“It’s nice when they are already singing and I don’t have to use the tape,” said Bowers,
Southwestern willow flycatchers require jungle-like riparian habitat for breeding – a rare-enough environment in this land of little rain, even in the best of circumstances. Given the impact on these rare oases by human development as well as drought, it’s no surprise that the population of these birds is sparsely and widely scattered across its range in the desert Southwest. That range includes Utah, Arizona, California, parts of Nevada, and New Mexico, where about40 percent of the total population occurs.
“Southwestern willow flycatchers are riparian obligates – they require riparian habitats also required by other species,” said Hira Walker, ornithologist for the New Mexico Department of Game and Fish. “Therefore, they can be considered ‘umbrella’ species; conservation efforts for this species can benefit many other riparian obligate wildlife and plant species.”
Other riparian species include Bell’s vireo, yellow-billed cuckoo, Lucy’s warbler, yellow-breasted chat, common yellowthroat, common black-hawk, vermilion flycatcher, and Gila woodpecker – all of which have occurred in the Lower Gila Box. Mammals such as black bears, mountain lions, bobcats, javelin, and the even the unusual coati also make the Box their home.
“Last year I came across about 35 coatis playing around like monkeys in one of these washes,” said Bowers. “One of them got a wild hair and climbed up a willow to knock another one out of the tree. They were hanging off the branches and hitting each other like cartoon characters.”
The Gila Lower Box is one of the increasingly rare areas in New Mexico that still retains a relatively intact native riparian ecosystem, with lentic or slow-moving
water, overbank flooding and dense multistory vegetation. Once immersed in the Lower Box, the threats and concerns of the world beyond seem almost unreal.
“Last year Clay (Bowers) radioed to say ‘These birds aren’t endangered! They’re packed in here!’” said Knox, adding that the Gila is not dammed upstream – one of the major factors that contributes to the healthy functioning of the ecosystem. The Lower Gila Box hosts the third largest population of Southwestern willow flycatchers in New Mexico, after the Cliff-Gila and San Marcial populations, according to Walker.
“All the features of the riparian habitat are in there and these birds seek it out and find it,” he said. State Land Office biologists monitor this and other sites to assure that the agency is managing the resource to sustain its productivity into the future.
“The idea is to identify any concerns that are present on lease sites relative to biota, erosion, pollution and conflicts of interest,” Knox said. “Oftentimes, endangered species are indicator species that highlight other problems in the ecosystem where they live. Monitoring the populations can provide insight about the overall health of those systems.”