CARLSBAD, N.M. (AP) — The sun sinks behind the western horizon, an orange glow lingers behind the fluorescent lights of an oil station northwest of Carlsbad. The faint whirr of oil pumps and chirp of crickets are all that can be detected by the human ear — but on other frequencies, it is not so quiet.
Sporting brown waders, a blue flannel shirt, and a headlamp, Dan Taylor, a biologist with Bat Conservation International, slips into a murky pond armed with long metal poles wrapped in netting, which he stretches across the water. Called a "mist net," it is the size of a volleyball net with mesh so fine it looks like smoke.
Taylor is attempting to capture bats as they swoop down to the pond for a drink of water.
A small yellow device with a red light is switched on. Called a bat detector, it picks up the sonic pulses used by bats for echolocation and translates them into clicking noises audible to the human ear.
"Big Brown bats can be as loud as a jackhammer," Taylor said. "You just can't hear them."
The device suddenly comes to life, with the clicks starting slow at first, then suddenly spiking in speed until it is almost a buzz.
Taylor explained the bat had likely just caught an insect, sending out more sonic pulses as it got closer to its prey.
Viewed through the ghostly green glow of the night vision goggles, another bat swoops down to the water, and then arcs gracefully over the top of the net. More clicks chirp from the detector.
"Sometimes you can almost hear them laugh at you," Taylor said.
He explained that although a bats' echolocation can detect something as fine as a human hair, they will sometimes become distracted by an insect or the surface of the water and fly into the net.
There are fewer bats out at night during the fall and winter months, he said. They often going into deep hibernation in the winter, or go into a deep sleep, called a torpor, only coming outside on warm days.
Still in his waders, Taylor slumps down on the bank and opens his laptop computer. Bat calls can be recorded and analyzed with various software. On screen, the calls can look like glowing blue hockey sticks or diagonal trails of dripping ink, which vary in shape and frequency by species.
Bat calls can range in frequency from less than 50 hertz, which is audible to humans, to more than 120 hertz, he said.
Locally, the rare Spotted bats, the massive Western Mastiff bats and larger free tail species can be heard by humans, often sounding like pings or chirps, he said.
Bats calls can also use harmonics — where a bat can call out on two different frequencies at exactly the same time.
The Western Mastiff can have a wingspan of two feet, and eats larger insects such as beetles, he said.
Mexican Free-tailed bats are common to the area and known for their large colony size. A colony of 1 million lives in the Carlsbad Caverns. Each Mexican Free-tailed bat can eat close to its own bodyweight in insects a night, Taylor said. Many of the bugs are considered pests to farmers.
This means the Carlsbad Caverns colony alone could eat 32,250 pounds of insects a night.
Bats are also responsible for pollinating many plants around the globe Taylor said. Many tropical fruits and the agave plant, which is used for tequila, are primarily pollinated by bats.
Farmers and orchard growers, such as pecan growers, are turning to bats as a natural source of pest control with quite a bit of success, he said.
There are many threats to bat populations in the Southwest, Taylor said. The most common are disturbance of habitat, such as the sealing of caves and mines for safety to humans and livestock, and dwindling surface waters during times of scarcity.
Wind turbines — a growing source of alternative electricity — are also dangerous to bats. Methods of audio deterrence and turbine speed regulation are currently being studied, he said.
Taylor also suggests that recreational cavers consult with a local wildlife agency before going down to prevent disturbing seasonal roosts.
Bats can be attracted by providing them with open drinking water and habitat for roosting. Taylor recommends placing bat houses at least 15 feet off the ground on the side of a house or barn facing the sun.
Bats drink on the wing, Taylor said, requiring long and calm stretches of water for them to swoop down and drink. Keeping stock tanks and ponds full allow them a consistent water source.
"A little bit of water can go a long way toward feeding a population," he said.
It is important however, to offer an escape ramp in stock tanks and livestock troughs for bats to escape if they fall in, he said, as well as an open flight path to the water's surface.
It gets late and Taylor sloshes back out into the water to retrieve his net. Not a single bat was caught that night, but he is undeterred.
"A bad day catching bats is better than a good day at the office," he said.