How to give a seabird an underwater hearing test

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The coasts are getting louder and louder, thanks to navigation, offshore drilling, wind turbines, naval sonar and a host of other ocean activities. While much research has examined how this cacophony can affect a range of marine life – whales, seals, sea turtles, and even fish – one notable group is missing: seabirds.

“In all fairness, 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 most of the time. of their life in the aquatic environment.

Berlin and his team are working to understand how ocean noise affects seabirds, but first they need to tackle a much more fundamental question: How well do seabirds hear? Which means figuring out how to get seabirds underwater hearing tests.

Of the two methods that the Berlin team is exploring, neither is without challenges. The first is known as the brainstem auditory response (ABR) and is the standard hearing test that most newborns receive. For seabirds, this is relatively quick and easy when done out of the water. A vet lightly calms the bird, and the researchers slide tiny electrodes under the skin of the bird’s head. Then, 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 of this underwater has been a challenge,” Berlin admits. They should keep the anesthetized birds submerged about a third of a meter underwater. In addition, since electricity and water do not mix, it has proven difficult to get the electrodes to correctly read the electrical outputs of the brain underwater.

The second type of hearing test involves 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 animals in captivity. Fortunately, the Berlin base of the Patuxent Wildlife Research Center in Maryland is home to a captive colony of around 140 seabirds, mostly diving ducks such as kakawi ducks, scoters and lesser scaups.

Training starts young, says Sara Crowell, who worked with ducklings who were just a few days old while a postdoctoral researcher at Patuxent. In the beginning, the objective is to get the ducklings to bang their beaks on a target buoy. “You wait for them to accidentally do it and reward them for it,” says Crowell. “They mounted it instantly.”

After learning the basics, the ducks eventually move on to underwater testing in a large diving pool. To begin the test, they are trained to hit a target, a pressure sensor illuminated by a blue LED about a third of a meter underwater, and, if they hear a tone, to hit a second target, illuminated by a white LED. If the ducks are doing well, a mealworm – “like chocolate to them,” Berlin says – falls from an automatic feeder, but if they are wrong or if they just peck the target repeatedly to try to get the treat, they get a “time out” in the dark.

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

Several parties are eagerly awaiting the results of the two tests. Understanding the hearing abilities of different species on land and underwater has many management applications. Once the Berlin team determines the underwater ABR, they can compare it with data collected from trained birds and hopefully create correction factors to improve the accuracy of the results from the Underwater ABR on wild birds. The US Navy, interested in the potential effects of sonar on wildlife, is funding underwater ABR testing. Meanwhile, the US Fish and Wildlife Service is getting involved in the hopes of creating a sound deterrent to reduce the accidental capture of seabirds in gillnets.

In the long run, Berlin and Crowell wonder how additional noise pressures can make coastal seabird migrations even more difficult. But, this question is still unanswered, even for much better studied marine mammals.

Andrew Wright, a marine mammal specialist at George Mason University, lists the known effects of noise: temporary and permanent hearing loss, interruption of feeding and reproduction, obscured communication, chronic stress, among others. One of the problems, he says, is adding up these effects, “we have little idea about the consequences this has for a population.” Whether and how these impacts affect seabirds – and how to extend protections – are also questions for the future.


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