By Joseph Robertia
The natural world is filled with the sounds of animals communicating with each other. To human ears, seagull shrieks and squirrel chatter may come more readily to ears and mind as the noises of the natural world, but moose can be plenty noisy, as well, using a variety of sounds to signal their intentions year-round.
Bulls rustle brush with their racks and grunt to females during the fall breeding season, cows emit soft whines and mews, and hidden calves bleat when they’re hungry to call their mom back to them.
Equally important to moose is their ability to hear sounds for their survival. The snapping of nearby twigs or rustling brush could mean that a predator, such as a bear or wolf, is on the hunt nearby.
“The soundscape — the cacophony of sounds that define a landscape — is very important to animals in their communication with each other and in their ability to listen to their environment,” said Tim Mullet, a doctoral candidate at the University of Alaska Fairbanks, currently involved in a two-year study of the relationship between sounds and moose on the Kenai National Wildlife Refuge.
Human-generated sound could be interfering with natural sounds, which subsequently may be stressing moose, or so goes Mullet’s hypothesis.
For anyone who has gone camping, this is an easily understood occurrence. Many choose a remote site in order to leave behind the sounds of the city. Perhaps a spot near a river or stream is chosen to listen to its natural rippling sounds, or possibly a site in the woods where a migratory bird’s song could be heard, or the sound of squirrels chattering over which should have a spruce cone. All it takes is one motor home to pull up nearby and run its generator all night for these sounds to be lost.
Mullet wonders if there may be parallels to moose whose environments are inundated by anthropogenic (human-generated) sounds, such as those created by snowmachines.
“Sound definitely has implications on ecology of animals,” Mullet said. “Previous studies have shown that anthropogenic sound has changed bird behavior. Some birds started calling at different times from what was normal for them.”
Snowmachines in winter aren’t the only non-natural sound producers. With a highway cutting through the refuge, the sound of vehicle traffic also contributes to the soundscape. An ATV hitting the trail or boats running on area lakes are common sounds of summer and fall, and planes flying overhead may be year-round contributors.
“We want to map these sounds, and look at what the differences are between summer and winter,” Mullet said.
There are seven permanent sound stations set up around the refuge, and six rotating stations are being used to take sound-level readings and recordings. The sound levels will be measured in decibels and graphed, while others are put through a spectrogram to determine their pitch.
“The intention is to map the distribution of decibel levels across the refuge and identify whether the source of those decibels is human-made or produced by nature,” Mullet said. “For sound pressures that exceed a certain decibel level, we will digitally record the sound in order to identify its source. Based on the spatial distribution of these sound samples, we will be able to create a map of sound sources within the landscape, which we will use to predict where sounds occur across the refuge and what those sounds are.”
Mullet also is collecting moose poop as part of his study and having it analyzed for levels of glucocorticoids — hormones that are indicators of animal stress. Chronic causes of high levels of these hormones can lower wildlife densities and displace animals from preferred habitats, Mullet said. He hopes to determine whether exposure to human-made noise causes such stress in moose on the refuge.
“We’re sampling weekly and hoping to get several hundred samples this winter, which we’re getting close to,” Mullet said. “We’re also sampling from several areas, including areas open and closed to snowmachining, to get a picture of the stress level differences in these areas.”
A management goal of the refuge is to conserve wildlife and its habitats while also balancing recreational opportunities, particularly when considering mandates imposed by the Wilderness Act of 1964. This legislation applies to 1.3 million acres of wilderness designated by Congress, within which the refuge is tasked with “retaining its primeval character and influence,” including “outstanding opportunities for solitude.”
Mullet’s study could assist refuge managers in understanding if noise from human activity is penetrating deeper into these wilderness areas.
“This is a fact-finding mission to find out what, if anything, is going on. We’re not getting into anything with displacement, we’re just looking at moose hormone levels in snowmachine areas versus non-use areas,” Mullet said. “I’m not biased and I’m not making any speculations. My goal is to be as objective as possible, and I’d like to involve snowmachine enthusiasts and clubs in the study.”