How to Give a Seabird an Underwater Hearing Test

Scientists are worried marine noise may affect seabirds, but first they have to figure out how to test it. 

Published August 25, 2016

The coasts are getting noisier, thanks to shipping, offshore drilling, wind turbines, naval sonar, and a slew of other ocean-based activities. While lots of research has examined how this cacophony may be affecting a range of marine life—whales, seals, sea turtles, even fish—one notable group is missing: seabirds.

“In all honesty, you just don’t think about underwater impacts on birds because they can fly,” says wildlife biologist Alicia Berlin, “but there are a lot of species that spend the majority of their lifetime in the aquatic environment.”

Berlin and her team are on a quest to understand how ocean noise affects seabirds, but first they must tackle a much more basic question: how well do seabirds hear? Which means figuring out how to give seabirds underwater hearing tests.

Of the two methods Berlin’s team is exploring, neither is without challenges. The first is known as auditory brainstem response (ABR) and is the standard hearing test most newborn babies receive. For seabirds, it’s relatively quick and easy when done out of water. A veterinarian slightly sedates the bird, and researchers slip tiny electrodes under the skin on the bird’s head. Next, a computer randomly plays a series of tones at different frequencies and decibel levels, and records the brainstem’s reaction to the sounds.

“Trying to do all that underwater has been a challenge,” admits Berlin. They have to maintain the anesthetized birds, submerged about a third of a meter underwater. Additionally, because electricity and water don’t mix, getting the electrodes to properly read the brain’s electrical outputs while underwater has proven difficult.

The second type of hearing test requires training seabirds to peck at a target when they hear a tone. It produces more reliable results, but is labor intensive and can only be used on captive animals. Fortunately, Berlin’s home base at the Patuxent Wildlife Research Center in Maryland has a captive colony of roughly 140 seabirds, mostly diving ducks such as long-tailed ducks, surf scoters, and lesser scaup.

Training starts young, says Sara Crowell, who worked with ducklings that were just a few days old while she was a postdoctoral researcher at Patuxent. Early on, the goal is getting the ducklings to tap their beaks on a target buoy. “You wait for them to do it accidentally and you reward them for it,” says Crowell. “They put it together instantaneously.”

After learning the basics, the ducks eventually move on to underwater trials in a large dive tank. To start the trial, they are trained to tap one target, a pressure sensor lit by a blue LED a third of a meter underwater, and, if they hear a tone, to tap a second target, lit by a white LED. If the ducks get it right, a mealworm—“like chocolate to them,” says Berlin—drops from an automatic feeder, but if they get it wrong or just peck the target repeatedly to try getting the treat, they get “time out” in the dark. 

Training is a long and tedious process, lasting about six months on average and fraught with complications including individual bird personalities, species differences, breeding season distractions, and even weekends. “My birds were very bad on Mondays because they had the weekend off,” says Crowell. “By Friday, we were doing great again.”

Several parties eagerly await the results of both tests. Understanding the hearing capabilities of different species on land and underwater has numerous management applications. Once Berlin’s team nails down underwater ABR, they can compare it with data collected from trained birds and hopefully create correction factors to improve the precision of results from underwater ABR on wild birds. The US Navy, interested in sonar’s potential effects on wildlife, is funding the underwater ABR tests. Meanwhile, the US Fish and Wildlife Service is pitching in with the hope of creating a sound-based deterrent to reduce seabird by-catch in gill nets.

Long term, both Berlin and Crowell wonder how added pressures from noise may make seabird coastal migrations even more arduous. But, this question is still unanswered even for much better studied marine mammals.

Andrew Wright, a marine mammalogist with George Mason University, lists the suite of known noise effects: temporary and permanent hearing loss, disrupted feeding and breeding, obscured communication, chronic stress, among many others. One problem, he says, is adding up these effects, “we have little idea what consequences that has for a population.” Whether and how these impacts translate to seabirds—and how to extend any protections—are also questions for the future.