Animal Superpower Can Bats and Dolphins See in the Dark
Transcript
00:00 Senses help different species navigate their world.
00:04 But some animals have incredible extra senses,
00:09 including dolphins.
00:12 This is the Dolphin Research Center
00:14 in Grassy Key in the heart of the Keys,
00:17 a chain of tropical islands off Florida's southernmost tip.
00:22 The dolphins here look like they're having fun,
00:26 and they do play all day.
00:28 But it's play with a purpose.
00:32 Researchers at the center are studying dolphin behavior
00:35 and intelligence.
00:39 The dolphins are mostly in it for the fish.
00:42 But these playful mammals do also enjoy attention.
00:46 [DOLPHIN SQUAWKING]
00:52 And they're as vocal as their trainers in their excitement.
00:55 [DOLPHIN SQUAWKING]
01:01 While most humans vocalize primarily through the air,
01:06 aquatic mammals do most of theirs underwater.
01:10 It turns out that's how dolphins manage
01:12 some of their best tricks.
01:13 [DOLPHIN SQUAWKING]
01:16 It's called echolocation.
01:21 Dolphins send out sounds and pick up
01:23 the echoes of those sounds to locate things.
01:25 This dolphin is going to find a ring tossed
01:30 underwater while blindfolded.
01:34 These are eye cups.
01:37 They cover the dolphin's eyes but come off easily
01:40 if he blinks.
01:43 Being playful, he returns them when they fall off.
01:46 For him, that's part of the game.
01:49 Before his trainer puts the eye cups on, she shows him a ring.
01:54 He's familiar with it by sight and touch.
01:57 He stores the mental picture in his brain.
02:01 Now she puts his eye cups on and sends him out to find it.
02:04 After searching around a little while, he finds the ring
02:12 and brings it back without the use of sight.
02:16 [DOLPHIN SQUAWKING]
02:19 Not a problem for a dolphin with a keen sense of hearing.
02:25 The ring doesn't make a sound on its own,
02:28 but sounds can bounce off the ring.
02:31 Dolphins improve their chances of sounds bouncing off objects
02:35 by making sounds themselves.
02:39 Little clicks.
02:41 They can be heard above the water's surface too.
02:43 [WATER SPLASHING]
02:46 They create the sounds using structures
02:54 inside their nasal cavities beneath the blowhole.
02:57 They're called phonic lips.
03:03 Every dolphin has two pairs of phonic lips
03:06 so they can make two clicks at the same time.
03:11 The clicks are short, measured in microseconds.
03:14 But they can make them in a constant series
03:17 called a click train.
03:18 Some clicks are at such high frequencies
03:23 human ears can't pick them up.
03:26 People only hear dolphin clicks at the lower frequency
03:29 of 20 kilohertz or less.
03:30 But dolphins send out their clicks
03:39 at frequencies of up to 120 kilohertz.
03:43 Even dogs known for picking up high pitched sounds
03:46 can't hear that.
03:49 So these dolphins are swimming effortlessly, but not
03:52 soundlessly, through the deep ocean.
03:55 It's one of the ways they find each other.
04:07 The outgoing sounds they produce with their phonic lips
04:09 are amplified as they pass through the bump
04:12 on the dolphin's head.
04:14 It's a fatty structure called the melon.
04:16 When the beam of sound encounters an object,
04:21 like a potential meal or another dolphin,
04:24 it bounces back, coming in through the mandible.
04:28 And the dolphin decodes the echoes
04:30 to tell what is out there.
04:31 It's a fast process.
04:36 Sound travels four times as fast in the water
04:38 as it does in the air.
04:41 So if a target is close, the dolphin
04:44 gets a mental picture in real time
04:46 with only a slight sound delay.
04:48 That mental picture includes a sense of how a target is moving
04:55 and where.
04:56 Since sound intensity decreases over distance,
04:59 some of the sound waves that bounce back to the dolphins
05:02 are very soft.
05:05 Dolphins' ears have evolved accordingly
05:07 and are some of the best of any animal.
05:10 These dolphins can demonstrate this, too.
05:14 His trainer is asking him to copy whatever
05:16 moves his fellow dolphin makes.
05:19 Once again, he's blindfolded.
05:20 That means the best way to figure out
05:31 what tricks the other dolphin is doing
05:33 is by hearing what the other dolphin does.
05:36 Time after time, he gets it right.
05:48 It's a super sense of hearing that's well worth celebrating.
05:57 [DOLPHIN SQUEAKS]
06:00 Echolocation is a useful super sense for another species.
06:11 These lesser funnel-eared bats are found
06:16 in the dry caves of the Bahamas.
06:20 They possess some enchanting natural powers.
06:25 Not only are they the world's only flying mammal,
06:32 but they can hunt with deadly efficiency
06:35 in the pitch black of night.
06:39 There are about 900 species of bat, and over half of them
06:44 use sound to navigate or echolocate.
06:47 Like dolphins, bats make a sound.
06:54 The sound bounces off objects around it and back to the bat.
07:01 Sounds simple, but how this actually happens
07:05 is anything but.
07:07 For a bat to see with sound, it has
07:09 to make a sound called a chirp.
07:13 Trouble is, for some bats, that chirp
07:15 is as loud as 120 decibels.
07:19 That's rock concert volume.
07:22 It's in the ultrasonic frequency range, which
07:25 means humans can't hear it.
07:28 But the bats can, and that decibel level
07:30 is loud enough to do serious damage to their ears.
07:34 Luckily, they've adapted the incredible ability
07:37 to essentially switch off their ears for just long enough
07:41 to save them from harm.
07:44 Six milliseconds before the larynx muscles
07:46 contract to blast out that sound,
07:49 the middle ear bones separate, and their hearing
07:52 sensitivity is reduced.
07:55 Two to eight milliseconds later, the middle ear muscles
07:58 relax and become sensitive again,
08:01 just in time to receive the much quieter echo.
08:05 Bats won't chirp again until the echo returns,
08:07 so as not to confuse themselves.
08:09 The echo of an insect one meter away
08:15 would take six milliseconds to return.
08:19 Having so much happen in such a short amount of time
08:22 seems just plain batty.
08:26 But it's the only way echolocation can work.
08:30 The initial chirp has to be that loud,
08:33 because it immediately starts losing power density.
08:37 When it hits an object and bounces back,
08:39 it loses even more density.
08:42 By the time the echo is heard by the bat,
08:44 it can be thousands of times quieter
08:46 than the original chirp.
08:51 The bat's ears are sensitive enough to hear this.
08:54 Even so, that's still not a lot of info to work with.
08:57 But the bat recalculates this information
09:03 hundreds of times per second, creating a highly detailed
09:07 picture of its surroundings.
09:10 As bats fly towards their prey, they
09:12 chirp at an accelerating rate, faster and faster,
09:16 until the echolocation calls reach mind-boggling levels.
09:21 The prey is caught.
09:24 160 to 190 chirps per second.
09:30 The bat's larynx can contract up to 200 times per second,
09:34 and the ear bones contract and relax for every single chirp.
09:40 This super sense is what makes bats
09:43 the most prolific night hunters the world has ever seen.
09:47 [music playing]
09:51 [chirping]
09:54 (water bubbling)