Whales whisper to their babies

Whales are some of the biggest animals on Earth, and when they call to each other, their songs can travel through the ocean for thousands of miles. But they’re not so large when they’re babies, and that’s when they could get eaten by predatory sharks or killer whales. This seems to be the reason behind a newly discovered, “quiet” form of whale call, that North Atlantic right whale mothers use when talking to their babies. Susan Parks, who made the finding, told Phil Sansom about these ‘whale whispers’...

Susan - We were studying communication of North Atlantic right whale mother-calf pairs and we were curious whether they would produce the normal louder sounds that these whales use for communication. So what we found was that they actually switched to producing a much quieter, sort of whisper type sound, to essentially hide from predators.

Phil - They’re like special sounds that you'd only say to your little kid then.

Susan - Yeah. I think just quiet little whispers to the baby.

Phil - Tell me a little about these whales, because I'd never heard of these before.

Susan - Right whales are one of the most endangered species of whales. They're only about 420 left in the world. They're baleen whales, which means they're filter feeders, so they swim really slowly through the water with their mouths open. They're not the most beautiful of whales. We can tell them apart because they have individually distinctive patterns growing on their head of finger like material, and these growths are covered with whale lice that are light in color and so they sort of make that pattern on their head stand out

Phil - Weird. Are they absolutely huge?

Susan - They are very very large, yeah. We go out in small boats and it's sort of one of the inspirational parts of my job when you have a whale swim under the boat and they're longer and wider than the small boat that you're on.

Phil - How many whales did you actually measure?

Susan - We were able to get tags on 16 whales to do the comparison.

Phil - Wow. Only 16.

Susan - That was how much we could get over six years of effort. North Atlantic right whales in particular have been having really sort of a hard time with reproduction in the populations, so very few calves have been born in the past few years. Most right whales that are killed now are accidentally killed by human activities. So they get hit by ships or they get entangled in fishing gear, and unfortunately mother-calf pairs seem to be a larger proportion of the individuals that are getting killed, to the point that two years ago there were no calves born for the entire species. And so it makes it really challenging to go out and collect data from mother-calf pairs when there are no calves.

Phil - And if they're so rare, how do you go out and find them and then listen to their sounds that they're making.

Susan - Yeah that's one of the biggest challenges in studying North Atlantic right whales - finding them in the first place. Where we were doing our study, which is off the states of Georgia and Florida in the United States, they're looking using an airplane to try to find the right whales in the area to help with their conservation, letting us know when there's a mother-calf pair in a particular area so we can take the boat out to find them.

Phil - And then what do you do once you get the boat out there?

Susan - We were using a small suction cup tag and we'll slowly approach that mother-calf pair and place the tag on the back of the mother. They spend a lot of time sleeping or resting and so we can approach them slowly with a vessel.

Phil - That's so strange that you're sneaking off on whales with suction cups to stick on their backs.

Susan - Yes it is a very strange image if I think about it, that what we do is that we have to very quietly sneak up on an enormous animal in the ocean and put a very small tag on their back.

Phil - What do the tags actually do?

Susan - So the tags record sound so we can hear the sounds that the whales make. And also the sounds that are in the environment around them. Right whales are really boring if you want to listen to a lot of whale sounds. In many habitats we'll get as low as one or two calls an hour. What we saw is that the juveniles and the pregnant females made a lot more of these louder long distance communication calls, and made very few sort of soft or quiet sounds. Whereas for the mother-calf pairs it was completely inverted, 90 percent of their sounds were these very very quiet, almost whisper-like sounds, and only about 10 percent of the sounds they made were these louder calls.

菲尔——这不是你经验ected, is that really strange?

Susan - What we expected actually is just to find that mother-calf pairs either didn't call very much at all or that they made the normal calls at a quieter level. So I was very surprised by essentially discovering this suite of sounds, these grunts and sort of pulse sounds that the mother-calf pairs were making, because it was something that we had never recorded before from right whales.

Phil - Why would they do that?

Susan - So right whales when they're adults really don't have any natural predators. The only time they're really vulnerable is when they're first born. So in the first few months of life, a young calf right whale is vulnerable to predation from killer whales and sharks. The only way they can hide from predators is to reduce their sound production. The water that they're in, you can't see very far because there's so much sediment in the water, so predators can't be finding them through vision.

Phil - And what are they saying to them when they're doing these grunts? Are they going “Oh, be quiet, there might be a killer whale nearby” or something?

Susan - My impression from the recordings is really that they're more just sort of keeping track of where the calf is, or letting the calf know where the mother is. They don't seem to be made in a particular context or a particular grouping of the sounds. They're sort of scattered throughout the recordings. For me what was most surprising is that it didn't even occur to us as scientists that they would do this sort of huge switch in the types of sounds they make. But I have a son myself and I know that the sounds that I would make to soothe him are things that I would never have made before he was born.