What do ducks hear? And why do we care?
It is not easy to help ducks. Ask Kate McGrew, a master’s student in wildlife ecology at the University of Delaware.
Over two seasons, 2016 and 2017, she spent months raising and working with more than two dozen hatchlings from three species, all to determine what they hear underwater.
This was no frivolous inquiry. Sea ducks, like the ones she trained, dive to catch their prey in oceans around the world and are often caught unintentionally in fish nets and killed.
Christopher Williams, a professor at the university who is McGrew’s adviser, said one estimate puts the number of ducks killed at sea at 400,000 a year, although he said the numbers are hard to pin down.
A similar problem plagues marine mammals, like whales, and acoustic devices have been developed to send out pings that warn them away from danger.
A similar tactic might work with diving ducks, but first, as Williams said, it would make sense to answer a question that science has not even asked about diving ducks: “What do they hear?”
“There actually is little to no research done on duck hearing in general,” McGrew said, “and on the underwater aspect of it, there’s even less.”
That is the recipe for a perfect, although demanding research project. Her goal was to use three common species of sea ducks to study a good range of underwater hearing ability. But while you can lead a duck to water and it will paddle around naturally, teaching it to take a hearing test is another matter entirely.
The training involved many steps. First she had to teach the ducklings to associate a sound with a treat. Then she had to get them to peck a target when they heard that sound.
Eventually the ducks had to learn to respond to a light by diving and pecking one target, and then, if they heard a sound while they were underwater, to surface and peck another target.
The ducks varied in learning ability, both by species and individual duckling. Over two years, only nine of 29 hatchlings made it to the final stages of the hearing test.
As for the differences in species, she said, “The long-tailed ducks are the smartest.” But, she said, they also try to cheat. She said they “try and get the reward without doing the correct behavior.”
Common eiders were too grouporiented to do any tests alone. “I was actually only able to train one individual,” McGrew said, of 11 hatchlings. “But she ended up being probably my most reliable duck.”
In the end, it turned out that the ducks heard well underwater in a range from 1 to 3 kilohertz. That is unfortunately close to the hearing range of fish, which can hear up to 2 kilohertz. And fishing operations do not want to warn the fish away.
Marine mammals hear at much higher frequencies, which makes commercial fishing operations more likely to use warning devices for them. This research is just a first step, though, in setting up a basic understanding of duck hearing ranges, so the practical applications for creating warning pingers for ducks are far in the future.