1 00:00:26,193 --> 00:00:30,155 Winter in the forests of North America. 2 00:00:33,408 --> 00:00:40,165 {\an8}A hushed world where billions of trees create a giant acoustic maze. 3 00:00:44,211 --> 00:00:47,714 And deep snow muffles sound. 4 00:00:51,134 --> 00:00:55,347 For the animals that live here, this is the stage 5 00:00:55,347 --> 00:01:02,187 for nature's greatest game of hide-and-seek. 6 00:01:08,360 --> 00:01:09,820 The red fox. 7 00:01:10,863 --> 00:01:14,241 The woodland's most acrobatic hunter. 8 00:01:18,412 --> 00:01:22,332 This young male is braving his first winter... 9 00:01:24,918 --> 00:01:27,713 and that means mastering the tricky challenge 10 00:01:27,713 --> 00:01:31,425 of catching prey hidden deep beneath the snow 11 00:01:32,259 --> 00:01:34,761 just by listening. 12 00:01:40,559 --> 00:01:45,689 He's after meadow voles, two feet under the surface. 13 00:01:49,484 --> 00:01:50,485 To keep hidden, 14 00:01:50,485 --> 00:01:57,075 they communicate in a secret language so high-pitched it's inaudible to us. 15 00:01:58,619 --> 00:02:03,582 But with specialist microphones, we can tune in to their calls. 16 00:02:10,881 --> 00:02:16,929 The voles use these eerie whistles to keep in touch through their tunnels... 17 00:02:23,852 --> 00:02:27,981 ...and to warn each other of danger. 18 00:02:42,913 --> 00:02:48,627 Unlike our ears, the foxes are attuned to the voles' every move. 19 00:02:52,673 --> 00:02:55,509 To work out exactly where they are, 20 00:02:56,134 --> 00:03:00,347 he uses a technique called triangulation. 21 00:03:03,225 --> 00:03:06,687 By comparing tiny differences in sound... 22 00:03:08,397 --> 00:03:12,651 hitting his left and right ear... 23 00:03:17,197 --> 00:03:22,452 he can pinpoint his prey to within two inches. 24 00:03:28,000 --> 00:03:30,836 Hearing them is one thing, 25 00:03:32,546 --> 00:03:34,923 but catching them is quite another. 26 00:03:39,303 --> 00:03:44,308 In the deep snow, every footstep gives him away. 27 00:03:53,317 --> 00:03:56,737 The voles sound their high-pitched alarm... 28 00:03:59,281 --> 00:04:00,949 and make their escape. 29 00:04:06,121 --> 00:04:10,000 For our young fox, learning this acoustic feat... 30 00:04:12,252 --> 00:04:13,587 takes trial... 31 00:04:18,175 --> 00:04:19,510 and error. 32 00:04:47,663 --> 00:04:48,497 This time... 33 00:04:51,291 --> 00:04:53,836 he's been outfoxed. 34 00:05:03,262 --> 00:05:09,560 But he's not the only forest predator listening for voles beneath the snow. 35 00:05:16,859 --> 00:05:19,361 The great gray owl... 36 00:05:21,446 --> 00:05:24,908 the woodland's ultimate acoustic hunter. 37 00:05:28,287 --> 00:05:31,832 Her hearing is even sharper than the fox's... 38 00:05:34,835 --> 00:05:41,466 thanks largely to the unique shape of her face. 39 00:05:44,970 --> 00:05:49,433 Her giant facial disc, the biggest of any owl, 40 00:05:49,433 --> 00:05:51,935 acts like a satellite dish... 41 00:05:55,939 --> 00:05:59,067 collecting and amplifying 42 00:06:00,402 --> 00:06:03,822 every tiny sound. 43 00:06:20,047 --> 00:06:22,466 It's a super-sense so powerful, 44 00:06:22,466 --> 00:06:28,430 she can hear a vole beneath the snow from 150 feet away. 45 00:06:39,733 --> 00:06:45,072 She's also the perfect stealth assassin. 46 00:06:47,824 --> 00:06:54,581 Special serrated feathers on her wings allow her to approach in complete silence. 47 00:06:57,626 --> 00:07:00,462 Constantly tracking her prey's position... 48 00:07:03,507 --> 00:07:05,008 just through sound. 49 00:07:17,437 --> 00:07:19,439 Only when she's locked on... 50 00:07:26,238 --> 00:07:27,406 will she strike. 51 00:07:41,170 --> 00:07:43,881 Thanks to their incredible hearing, 52 00:07:44,715 --> 00:07:49,845 65% of great gray owl hunts end in a meal. 53 00:08:04,318 --> 00:08:09,823 After six cold months, North America's forests begin to warm, 54 00:08:11,074 --> 00:08:15,120 and otherworldly sounds fill the airwaves. 55 00:08:19,791 --> 00:08:23,962 Frozen lakes shift and crack. 56 00:08:28,509 --> 00:08:32,971 Microphones above and below the surface 57 00:08:32,971 --> 00:08:35,640 capture the sound of each fracture. 58 00:08:38,936 --> 00:08:44,107 Higher notes travel through the ice faster than the lower ones... 59 00:08:46,777 --> 00:08:49,863 creating these sonic pulses. 60 00:08:56,328 --> 00:09:01,083 A rare phenomenon heard only a few days a year. 61 00:09:03,877 --> 00:09:07,005 It's a sign the soundscape of these forests 62 00:09:07,548 --> 00:09:11,635 is about to undergo a radical transformation. 63 00:09:18,475 --> 00:09:20,102 Under the strengthening sun, 64 00:09:20,978 --> 00:09:24,231 snow covering half the continent of North America... 65 00:09:27,818 --> 00:09:29,027 starts to melt. 66 00:09:36,034 --> 00:09:39,246 Releasing trillions of gallons of fresh water... 67 00:09:44,334 --> 00:09:46,587 it turns icy trickles... 68 00:09:49,506 --> 00:09:51,466 into raging rivers. 69 00:09:58,015 --> 00:10:01,852 Now these northern forests are filled with the sounds... 70 00:10:04,855 --> 00:10:05,856 of new life. 71 00:10:17,367 --> 00:10:18,994 And deep in the woods... 72 00:10:21,121 --> 00:10:24,666 hidden cameras capture the debut performance 73 00:10:24,666 --> 00:10:28,962 of one of America's most secretive animals. 74 00:10:32,508 --> 00:10:34,760 This four-week-old wolf pup... 75 00:10:35,802 --> 00:10:39,389 is emerging from the den for the very first time. 76 00:10:42,893 --> 00:10:44,728 With his parents off hunting, 77 00:10:44,728 --> 00:10:47,189 he starts to practice... 78 00:10:47,189 --> 00:10:49,691 the iconic wolf howl. 79 00:10:52,236 --> 00:10:55,155 Well, everyone has to start somewhere. 80 00:11:06,583 --> 00:11:10,420 Each pup has a unique voice 81 00:11:10,420 --> 00:11:15,008 that holds important information about their place in the hierarchy. 82 00:11:18,887 --> 00:11:20,639 Even at this age, 83 00:11:20,639 --> 00:11:24,935 the more dominant the wolf, the deeper the call. 84 00:11:38,532 --> 00:11:42,870 Howling also plays a key role in keeping the pack together. 85 00:11:53,755 --> 00:11:57,968 Sometimes more adventurous pups wander off. 86 00:12:03,807 --> 00:12:07,227 And these woods are no place to be alone. 87 00:12:10,939 --> 00:12:13,150 Bumping into a black bear... 88 00:12:15,694 --> 00:12:17,029 would not end well. 89 00:12:29,416 --> 00:12:31,043 To find his way home, 90 00:12:31,627 --> 00:12:36,924 this little wolf needs to use his brand-new howl. 91 00:13:04,284 --> 00:13:05,827 Through sound... 92 00:13:07,037 --> 00:13:08,580 they're reunited. 93 00:13:13,710 --> 00:13:19,091 In just a year's time, their adult howls will allow them to keep in touch... 94 00:13:19,675 --> 00:13:21,635 ...from seven miles away. 95 00:13:27,933 --> 00:13:29,434 As spring progresses, 96 00:13:30,227 --> 00:13:33,647 a more peculiar noise cuts through the forest... 97 00:13:38,402 --> 00:13:42,531 produced by an unlikely little animal. 98 00:13:43,991 --> 00:13:46,034 The ruffed grouse. 99 00:13:50,163 --> 00:13:53,250 A plump little bird full of surprises. 100 00:13:57,880 --> 00:14:03,385 This amorous male is hoping to attract a partner. 101 00:14:06,680 --> 00:14:10,726 Like all ruffed grouse, he's no singer. 102 00:14:13,896 --> 00:14:16,565 But he is a drummer. 103 00:14:36,001 --> 00:14:40,631 He belts out this mating beat more than 12 hours a day. 104 00:14:49,181 --> 00:14:50,474 But in these woods... 105 00:14:51,767 --> 00:14:53,602 ...broadcasting your whereabouts 106 00:14:53,602 --> 00:14:57,981 at top volume is a dangerous game. 107 00:15:01,610 --> 00:15:03,654 Goshawks patrol here. 108 00:15:09,785 --> 00:15:15,290 And a portly grouse would make an ample meal. 109 00:15:18,919 --> 00:15:22,923 He somehow needs to make himself heard by potential mates 110 00:15:22,923 --> 00:15:25,968 without attracting unwanted attention. 111 00:15:29,763 --> 00:15:31,139 For the first time, 112 00:15:31,139 --> 00:15:35,686 super slow-motion cameras reveal how he does it. 113 00:15:40,148 --> 00:15:45,612 With each wing beat, the lower feathers flick forwards, 114 00:15:46,905 --> 00:15:48,907 scooping up a pocket of air... 115 00:15:54,079 --> 00:15:55,914 creating a loud boom... 116 00:16:00,878 --> 00:16:04,006 which is channeled directly in front of him. 117 00:16:10,220 --> 00:16:15,976 Strangely, from the side, just a faint fluttering can be heard. 118 00:16:21,398 --> 00:16:27,154 But from in front, it's three times louder, 119 00:16:28,822 --> 00:16:34,870 allowing him to broadcast his call only in the direction of potential mates. 120 00:16:38,207 --> 00:16:43,086 And his efforts are paying off. 121 00:16:45,339 --> 00:16:48,258 A female attracted by his beat. 122 00:16:51,386 --> 00:16:55,849 Now he must make sure he looks as impressive... 123 00:16:58,852 --> 00:17:00,395 as he sounds. 124 00:17:03,148 --> 00:17:05,025 It seemed to be going well. 125 00:17:07,528 --> 00:17:09,863 But at the first hint of danger... 126 00:17:13,700 --> 00:17:15,243 he chickens out. 127 00:17:25,628 --> 00:17:28,298 As the forests continue to heat up... 128 00:17:28,298 --> 00:17:32,427 even the trees start making bizarre noises. 129 00:17:35,722 --> 00:17:40,269 Microphones beneath the bark capture strange gurgles... 130 00:17:43,647 --> 00:17:47,734 as cottonwood trees slurp up water from their roots. 131 00:17:55,450 --> 00:17:58,412 But as summer draws to a close... 132 00:18:01,456 --> 00:18:03,417 the airwaves are filled... 133 00:18:07,171 --> 00:18:12,384 with the unmistakable sound of the elk. 134 00:18:19,474 --> 00:18:23,228 Their unusual call is known as a bugle, 135 00:18:23,812 --> 00:18:27,983 and it means it's almost time for them to breed. 136 00:18:33,405 --> 00:18:37,201 This majestic old bull is the boss around here. 137 00:18:42,414 --> 00:18:46,835 He guards a large herd of females known as a harem. 138 00:18:47,753 --> 00:18:52,132 But at ten years old, this could be his last season at the top. 139 00:18:53,926 --> 00:18:55,636 For the next month, 140 00:18:55,636 --> 00:19:00,933 keeping rivals away will all come down to his ability to bugle. 141 00:19:06,438 --> 00:19:11,235 It's his way of telling other males to back off. 142 00:19:12,903 --> 00:19:15,739 And it's more complex than you might think. 143 00:19:19,701 --> 00:19:24,581 The elk's strange call is made up of two different sounds 144 00:19:24,581 --> 00:19:30,420 produced simultaneously, known as biphonation. 145 00:19:33,006 --> 00:19:36,718 By slowing down and separating these sounds... 146 00:19:38,679 --> 00:19:41,890 we can hear a high, piercing whistle... 147 00:19:45,936 --> 00:19:48,772 as well as a deep, bellowing roar. 148 00:19:53,694 --> 00:19:56,947 The low notes give an accurate measure of size. 149 00:20:07,457 --> 00:20:11,211 The bigger the male, the deeper the bellow. 150 00:20:14,131 --> 00:20:17,134 But these don't travel far through the forest. 151 00:20:17,926 --> 00:20:23,432 The high notes give less information about size but carry far further. 152 00:20:33,692 --> 00:20:36,653 They can be heard from a mile away... 153 00:20:41,700 --> 00:20:43,410 by rival males. 154 00:20:44,953 --> 00:20:49,499 The high whistle alone is usually enough to scare off the competition. 155 00:20:52,544 --> 00:20:56,298 But this interloper has other ideas. 156 00:21:02,638 --> 00:21:04,806 Calling back is a direct challenge... 157 00:21:09,019 --> 00:21:13,357 and an unwelcome sound for the old bull. 158 00:21:30,624 --> 00:21:33,168 As the intruder closes in, 159 00:21:33,168 --> 00:21:39,049 both males try and intimidate each other with their deepest roars. 160 00:21:42,219 --> 00:21:45,806 But these two are evenly matched. 161 00:21:51,687 --> 00:21:53,522 To hold on to his harem, 162 00:21:54,523 --> 00:21:59,653 the old bull now has no option but to fight. 163 00:22:22,217 --> 00:22:24,636 Lasting up to 30 minutes, 164 00:22:24,636 --> 00:22:28,891 the aim is to wear down and exhaust the opponent. 165 00:22:51,788 --> 00:22:55,042 The old bull sends the interloper packing. 166 00:23:00,797 --> 00:23:04,885 Now he has one last sound trick to play. 167 00:23:09,348 --> 00:23:10,849 A victory bugle. 168 00:23:12,851 --> 00:23:19,733 Elk are the only mammals besides humans thought to use sound to celebrate victory. 169 00:23:29,618 --> 00:23:30,869 In just four weeks... 170 00:23:34,122 --> 00:23:37,835 these noisy bugling contests will be over. 171 00:23:41,296 --> 00:23:44,633 It won't be long before the temperature starts to drop 172 00:23:45,843 --> 00:23:49,346 and the volume fades down once again 173 00:23:50,264 --> 00:23:53,058 in the forests of North America. 174 00:24:05,821 --> 00:24:10,450 To capture the spectacular drumming solos of the ruffed grouse 175 00:24:10,450 --> 00:24:14,413 like never before, the Earthsounds team traveled 176 00:24:14,413 --> 00:24:17,082 deep into the forests of Minnesota 177 00:24:18,792 --> 00:24:21,211 where they searched out fallen logs, 178 00:24:22,212 --> 00:24:25,757 the sound stage from which the grouse perform. 179 00:24:28,093 --> 00:24:30,846 For sound recordist, Nick McMahan, 180 00:24:30,846 --> 00:24:35,517 recording the audio of this behavior should be relatively straightforward. 181 00:24:36,351 --> 00:24:40,272 I'm very fortunate that the ruffed grouse will be drumming right on the log here. 182 00:24:40,272 --> 00:24:43,734 {\an8}So, it's-- it's much more accessible than the birds that are up, 183 00:24:44,443 --> 00:24:46,737 {\an8}in the trees singing up above us. 184 00:24:48,155 --> 00:24:51,533 Male ruffed grouse move from log to log in the forest, 185 00:24:52,451 --> 00:24:56,747 and on each one, they can drum for up to three hours. 186 00:24:58,373 --> 00:25:01,126 As the grouse does its drumming performance, 187 00:25:01,126 --> 00:25:02,836 it's moving its feathers very quickly. 188 00:25:02,836 --> 00:25:05,923 And so, I'm hoping that some of the feather motion 189 00:25:05,923 --> 00:25:09,176 and the-- and the movement of that will be captured with these microphones. 190 00:25:10,469 --> 00:25:13,764 Nick sets up a remote camera to record 191 00:25:13,764 --> 00:25:19,186 when the grouse displays and leaves his microphones running. 192 00:25:19,937 --> 00:25:22,064 But for cameraman, Dawson Dunning, 193 00:25:22,648 --> 00:25:27,027 capturing the visual display is more of a challenge. 194 00:25:29,154 --> 00:25:31,698 {\an8}You can't necessarily just walk up to these birds and film them. 195 00:25:31,698 --> 00:25:33,450 {\an8}They're actually quite skittish. 196 00:25:33,951 --> 00:25:36,912 {\an8}They'll tolerate you kind of being around, but they won't perform. 197 00:25:37,871 --> 00:25:41,250 To make sure he doesn't give the grouse stage fright, 198 00:25:41,250 --> 00:25:44,628 Dawson sets up a camera he can operate remotely. 199 00:25:46,463 --> 00:25:49,216 But to show how the sound is produced, 200 00:25:49,216 --> 00:25:52,386 he also wants to capture it in super slow motion. 201 00:25:54,054 --> 00:25:58,976 And that means using a specialist camera from a hide a distance away. 202 00:26:00,018 --> 00:26:03,522 I think what this slow-motion camera will really allow us to do is see the path 203 00:26:03,522 --> 00:26:07,401 of the wings and, kind of, how they're actually pushing the air 204 00:26:07,401 --> 00:26:10,779 to create this sonic boom sound. 205 00:26:10,779 --> 00:26:13,323 So, this is really the only way we can slow it down enough 206 00:26:13,323 --> 00:26:15,534 to see how the feathers are moving. 207 00:26:15,534 --> 00:26:17,911 Otherwise, it's just a blur to our eye. 208 00:26:21,832 --> 00:26:26,545 With everything set up, the waiting game begins. 209 00:26:29,506 --> 00:26:31,842 Sometimes he'll, like-- he won't come here for hours 210 00:26:31,842 --> 00:26:34,094 because he's stuck somewhere else on another log 211 00:26:34,094 --> 00:26:37,848 and I'm just sitting here doing nothing because, you know, 212 00:26:37,848 --> 00:26:40,142 I just have to wait for him to show up. 213 00:26:40,726 --> 00:26:44,438 After days of trying and failing, 214 00:26:45,856 --> 00:26:48,317 Dawson's luck starts to change. 215 00:26:50,986 --> 00:26:53,071 Can hear him coming on the leaves. 216 00:26:57,826 --> 00:26:58,785 Yeah. There he is. 217 00:27:04,416 --> 00:27:08,295 At first, the bird seems a little shy. 218 00:27:12,424 --> 00:27:14,927 But then his confidence builds... 219 00:27:17,638 --> 00:27:22,726 allowing Dawson to finally film the perfect drum solo. 220 00:27:29,233 --> 00:27:30,526 That's so cool. 221 00:27:30,526 --> 00:27:33,862 I can just feel that sound just hit your chest. 222 00:27:35,447 --> 00:27:36,448 Look at that. 223 00:27:37,407 --> 00:27:38,492 That was amazing. 224 00:27:44,831 --> 00:27:47,709 Using this super slow-motion camera, 225 00:27:47,709 --> 00:27:50,963 you can see the path of their wings and really how they're creating 226 00:27:50,963 --> 00:27:52,840 this amazing sound. 227 00:27:56,927 --> 00:28:00,722 They're doing, like, 50 of these wing beats in one little quick session. 228 00:28:02,015 --> 00:28:04,184 After three weeks in the forest, 229 00:28:04,726 --> 00:28:08,981 the team manages to capture the drumming shows like never before 230 00:28:10,107 --> 00:28:13,527 and reveal how these plucky birds produce, 231 00:28:13,527 --> 00:28:18,574 surely, the most unusual sounds in the woodlands of North America.