1 00:00:38,487 --> 00:00:41,479 Hidden forces shroud our world. 2 00:00:41,527 --> 00:00:45,486 0n this journey, we glimpse their presence. 3 00:00:48,287 --> 00:00:51,563 The aurora borealis sweeping the northern skies 4 00:00:51,607 --> 00:00:55,122 can be a sign all is not well in the heavens. 5 00:00:58,447 --> 00:01:01,280 When magnetic storms rage on the sun, 6 00:01:01,327 --> 00:01:03,887 charged particles bombard the earth, 7 00:01:03,927 --> 00:01:08,682 creating curtains of light as they collide with the atmosphere. 8 00:01:14,007 --> 00:01:16,362 To migrants, such as starlings, 9 00:01:16,407 --> 00:01:20,195 these northern lights have a darker side. 10 00:01:26,207 --> 00:01:32,123 The sun“s magnetic storms can cause chaos in both our worlds. 11 00:01:32,167 --> 00:01:36,558 Power surges in the atmosphere can trip the electric grid. 12 00:01:42,567 --> 00:01:46,082 Away from land, the effects can be devastating, 13 00:01:46,127 --> 00:01:49,119 especially if the weather worsens. 14 00:01:54,447 --> 00:01:58,838 The earth“s magnetic field warps, deflecting compasses. 15 00:02:00,007 --> 00:02:03,204 Radio transmissions suffer interference. 16 00:02:07,247 --> 00:02:10,319 The starlings“ sense of direction is affected, too. 17 00:02:10,367 --> 00:02:13,325 Lost at sea, they head for shelter. 18 00:02:34,247 --> 00:02:37,444 0ther forces now materialise. 19 00:02:37,487 --> 00:02:41,639 St Elmo“s fire, a ghostly glow of energised air, 20 00:02:41,687 --> 00:02:44,326 warns of imminent lightning. 21 00:02:44,367 --> 00:02:46,198 (Thunderclap) 22 00:03:03,927 --> 00:03:07,442 In the past, the seasonal coming and going of birds 23 00:03:07,487 --> 00:03:09,478 was considered supernatural. 24 00:03:13,527 --> 00:03:15,119 Enter their world 25 00:03:15,167 --> 00:03:18,603 and the hidden forces now known to guide their migrations 26 00:03:18,647 --> 00:03:20,797 appear just as remarkable. 27 00:03:25,047 --> 00:03:29,279 Each autumn, greylag geese fly nearly a thousand kilometres 28 00:03:29,327 --> 00:03:31,602 from Iceland to Britain. 29 00:03:32,927 --> 00:03:35,964 They use hidden forces to predict the weather 30 00:03:36,007 --> 00:03:40,319 and ensure the flock sets off under favourable conditions. 31 00:03:55,887 --> 00:03:58,799 0ther forces, such as the earth“s magnetic field, 32 00:03:58,847 --> 00:04:01,441 help the geese keep on course. 33 00:04:03,367 --> 00:04:06,882 We“ve only just begun to unravel the magnetic senses 34 00:04:06,927 --> 00:04:11,000 that guide animals across an often featureless world. 35 00:04:14,767 --> 00:04:17,281 Some of their feats defy belief. 36 00:04:22,967 --> 00:04:25,606 These green turtle hatchlings 37 00:04:25,647 --> 00:04:29,242 are starting a nomadic life roaming the oceans. 38 00:04:30,207 --> 00:04:35,440 It will be 30 years before they return here to breed. 39 00:04:35,487 --> 00:04:38,479 Somehow they find this remote beach again. 40 00:04:38,527 --> 00:04:41,599 The secret lies in tiny magnetised particles 41 00:04:41,647 --> 00:04:44,036 known as magnetite. 42 00:04:46,527 --> 00:04:48,961 These internal magnets may sense 43 00:04:49,007 --> 00:04:51,237 both the strength of the magnetic field 44 00:04:51,287 --> 00:04:53,847 as well as its angle to the earth. 45 00:04:58,007 --> 00:05:01,204 These two forces act like grid lines on a map. 46 00:05:01,247 --> 00:05:05,240 Any point in the ocean has its own unique coordinates. 47 00:05:23,527 --> 00:05:25,916 (Squawking) 48 00:05:28,607 --> 00:05:32,885 Brown pelicans also use magnetite, but new findings have found 49 00:05:32,927 --> 00:05:35,725 that birds possess an additional system. 50 00:05:35,767 --> 00:05:38,406 Vision is involved. 51 00:05:44,287 --> 00:05:49,645 Specialised magnetic sensors have been identified in the retina. 52 00:05:49,687 --> 00:05:52,838 These see a coloured spot that shows the position 53 00:05:52,887 --> 00:05:54,878 of the magnetic pole. 54 00:06:01,447 --> 00:06:05,759 This head-up display allows the birds to navigate uncharted waters 55 00:06:05,807 --> 00:06:09,004 by providing a constant compass bearing. 56 00:06:19,047 --> 00:06:21,481 Like trawler men, they use their compass 57 00:06:21,527 --> 00:06:24,724 to find the richest fishing grounds. 58 00:06:33,647 --> 00:06:36,366 A free lunch is irresistible. 59 00:07:31,287 --> 00:07:35,439 There are yet other ways to sense the earth“s magnetism. 60 00:07:39,447 --> 00:07:41,756 Hammerhead sharks are so perceptive, 61 00:07:44,847 --> 00:07:49,159 they can detect local variations of magnetism in underlying rock. 62 00:07:49,207 --> 00:07:51,926 They seem to congregate where magnetised lava 63 00:07:51,967 --> 00:07:56,245 from an extinct volcano creates an invisible landmark. 64 00:07:58,167 --> 00:08:02,638 At night, sharks leave their staging post and follow hidden roadways 65 00:08:02,687 --> 00:08:06,362 marked by abrupt changes in magnetic intensity. 66 00:08:08,247 --> 00:08:11,159 The bizarre head enhances sensitivity 67 00:08:11,207 --> 00:08:15,359 to these local distortions in the earth“s field. 68 00:08:19,247 --> 00:08:23,445 Sharks use electrosensors to detect magnetism. 69 00:08:23,487 --> 00:08:27,480 The same sensors home in on the body fields of their prey. 70 00:08:28,367 --> 00:08:34,124 Their widened head spaces out the sensors, increasing sensitivity. 71 00:08:49,247 --> 00:08:52,444 A sense so acute is easily confused. 72 00:08:52,487 --> 00:08:54,478 (Sonar pinging) 73 00:08:56,367 --> 00:08:59,484 A nuclear submarine tows a hydrophonic array 74 00:08:59,527 --> 00:09:01,518 to detect other submarines. 75 00:09:09,727 --> 00:09:13,037 The array gives off electric and magnetic waves. 76 00:09:13,087 --> 00:09:16,716 Sharks find the combination irresistible. 77 00:09:23,247 --> 00:09:25,556 These hydrophones are being redesigned 78 00:09:25,607 --> 00:09:28,167 to prevent damage from shark attacks. 79 00:09:28,207 --> 00:09:30,198 (Low electrical drone ) 80 00:09:31,367 --> 00:09:35,360 Fire ants share the sharks“ passion for electricity. 81 00:09:36,207 --> 00:09:39,722 Introduced into America from Brazil in the 1930s, 82 00:09:39,767 --> 00:09:43,999 the ants soon acquired a strange interest in technology. 83 00:09:44,047 --> 00:09:46,038 (Low electrical drone ) 84 00:09:47,847 --> 00:09:52,045 Perhaps they mistake electricity for the body fields of their prey. 85 00:09:52,087 --> 00:09:53,679 No one really knows. 86 00:09:53,727 --> 00:09:57,879 What is known is the chaos caused by the ants. 87 00:09:57,927 --> 00:10:00,760 (Car horns blare ) 88 00:10:00,807 --> 00:10:04,482 By severing wires and creating short circuits, 89 00:10:04,527 --> 00:10:07,997 fire ants are the ultimate gremlins in the machine. 90 00:10:08,047 --> 00:10:10,038 (Car horns and sirens ) 91 00:10:13,167 --> 00:10:16,204 In homes, they seek the electromagnetic waves 92 00:10:16,247 --> 00:10:19,683 given off by domestic appliances. 93 00:10:25,527 --> 00:10:29,406 A microwave oven makes an irresistible target. 94 00:10:41,087 --> 00:10:46,957 Electrical attraction lures the ants into this potential hot spot. 95 00:11:03,367 --> 00:11:06,757 But techno ants are not easily destroyed. 96 00:11:10,087 --> 00:11:14,638 Fire ants are so small, most of the microwave energy misses them. 97 00:11:14,687 --> 00:11:16,803 They also sense cooler zones. 98 00:11:16,847 --> 00:11:21,443 If hot spots build up, unlike food, they can quickly move away. 99 00:11:23,287 --> 00:11:26,040 Fire ants are aptly named. 100 00:11:26,087 --> 00:11:28,203 Their stings burn. 101 00:11:28,247 --> 00:11:31,125 - (Screams ) - (Car horns blare ) 102 00:11:31,167 --> 00:11:33,158 (Tyres screech, crashing) 103 00:11:37,567 --> 00:11:39,797 Every year, across the southern States, 104 00:11:39,847 --> 00:11:43,442 fire ants cause millions of dollars“ worth of damage. 105 00:11:43,487 --> 00:11:45,478 (Siren wails) 106 00:11:52,807 --> 00:11:55,002 (Woman ) There were ants in my pizza... 107 00:11:55,047 --> 00:11:59,837 As each queen ant can spawn a colony of 30,000 individuals, 108 00:11:59,887 --> 00:12:03,880 this alien invasion has proved impossible to repel. 109 00:12:09,007 --> 00:12:11,726 Because of concerns about possible risks 110 00:12:11,767 --> 00:12:15,316 from electromagnetic forces, homes are now rarely built 111 00:12:15,367 --> 00:12:18,200 under high-voltage power lines. 112 00:12:18,247 --> 00:12:20,636 (Low electrical drone ) 113 00:12:20,687 --> 00:12:24,680 Through, strangely enough, plants appear to thrive here. 114 00:12:28,367 --> 00:12:31,245 They find electromagnetic fields stimulating. 115 00:12:40,807 --> 00:12:43,480 Changes to electric charges in plants 116 00:12:43,527 --> 00:12:45,882 affect hormones controlling growth. 117 00:12:45,927 --> 00:12:48,964 Perhaps these forces help the process. 118 00:13:01,287 --> 00:13:04,677 Electricity is not always so appreciated. 119 00:13:04,727 --> 00:13:09,118 Bees will desert hives placed under power lines. 120 00:13:11,447 --> 00:13:14,723 The explanation may lie in the bees“ own electric charge, 121 00:13:14,767 --> 00:13:19,124 generated by friction with the air as it flies. 122 00:13:20,287 --> 00:13:23,643 The bees make good use of this static charge. 123 00:13:25,567 --> 00:13:27,558 Pollen is positively charged 124 00:13:27,607 --> 00:13:32,237 and is attracted to the negatively charged bee, even while it“s flying. 125 00:13:37,407 --> 00:13:41,195 For a busy bee, this remote pickup saves time. 126 00:13:41,247 --> 00:13:43,966 The prize is stored in a pollen sac. 127 00:13:45,927 --> 00:13:49,158 Bees probably swarm away from power lines 128 00:13:49,207 --> 00:13:53,086 because of interference with the bees“ static charges. 129 00:13:55,367 --> 00:13:57,801 Any electric field disturbs them. 130 00:14:02,047 --> 00:14:06,643 The bees react aggressively to electricity, as though under threat. 131 00:14:08,527 --> 00:14:11,519 Guard bees defend the colony at all cost. 132 00:14:20,927 --> 00:14:24,317 They target any source of electricity. 133 00:15:01,287 --> 00:15:04,597 We“ve learnt to harness many electrical forces. 134 00:15:04,647 --> 00:15:06,877 But the untamed electricity of nature 135 00:15:06,927 --> 00:15:09,395 unleashes even stronger powers. 136 00:15:15,527 --> 00:15:17,518 (Thunderclap) 137 00:15:21,447 --> 00:15:26,601 Besides these static discharges, the air holds far subtler charges. 138 00:15:26,647 --> 00:15:30,720 Concentrations of charged molecules, known as air ions, 139 00:15:30,767 --> 00:15:33,156 change with the weather. 140 00:15:37,287 --> 00:15:41,041 Snakes may have the power to detect these air ions. 141 00:15:42,367 --> 00:15:45,484 Friction causes static charges to build up on a snake, 142 00:15:45,527 --> 00:15:47,916 just as they do on a bee. 143 00:15:51,447 --> 00:15:54,120 Because the snake“s skin is a good insulator, 144 00:15:54,167 --> 00:15:58,524 it“s perfectly adapted to hold static electricity. 145 00:16:09,807 --> 00:16:12,401 The synthetic clothing used by cyclists 146 00:16:12,447 --> 00:16:15,519 holds static charges in the same way. 147 00:16:21,487 --> 00:16:23,239 (Hissing rattle ) 148 00:16:23,287 --> 00:16:26,996 The snake uses the rattle as a warning. 149 00:16:32,247 --> 00:16:35,239 0ur static is easily discharged. 150 00:16:43,207 --> 00:16:46,597 But the snake“s dry skin holds its charge. 151 00:16:48,087 --> 00:16:51,318 The rattle also generates static by friction 152 00:16:51,367 --> 00:16:54,996 and this could top up the snake“s static electricity. 153 00:16:55,047 --> 00:16:59,199 0nce the snake is charged up, its forked tongue could be deflected 154 00:16:59,247 --> 00:17:02,125 by other charges in the air. 155 00:17:03,327 --> 00:17:07,798 By sensing this deflection, the snake would detect air ions. 156 00:17:08,967 --> 00:17:12,596 Air ions are exhaled in the breath of prey. 157 00:17:12,647 --> 00:17:16,162 They also drift from holes in the ground. 158 00:17:18,367 --> 00:17:20,961 The snake may use this extrasensory system 159 00:17:21,007 --> 00:17:23,396 to its own advantage. 160 00:17:24,887 --> 00:17:26,798 (Squeaking) 161 00:17:26,847 --> 00:17:31,841 The snake“s tongue is better known in its role as an organ of smell. 162 00:17:45,327 --> 00:17:48,125 The orange ladybird has extraordinary powers 163 00:17:48,167 --> 00:17:50,727 of sensing hidden forces. 164 00:17:50,767 --> 00:17:54,521 It forecasts the unpredictable British winter. 165 00:17:59,167 --> 00:18:04,116 Human meteorologists consider such long-range prediction impossible. 166 00:18:04,167 --> 00:18:07,204 But the ladybird can choose its overwintering site 167 00:18:07,247 --> 00:18:10,364 depending on the weather to come. 168 00:18:10,407 --> 00:18:12,762 If the winter outlook is mild, 169 00:18:12,807 --> 00:18:16,163 it selects exposed spots like this weather screen. 170 00:18:16,207 --> 00:18:19,358 If harsh, it spends the winter underground. 171 00:18:23,167 --> 00:18:27,126 A hundred ladybirds may choose the same location, 172 00:18:27,167 --> 00:18:30,603 one offering just enough protection. 173 00:18:37,047 --> 00:18:43,122 In these exposed sites, they may still experience the odd cold snap. 174 00:18:51,647 --> 00:18:54,036 They can even be quick-frozen. 175 00:18:54,087 --> 00:18:58,365 Providing the temperature stays above a critical minus ten degrees, 176 00:18:58,407 --> 00:19:01,126 the ladybirds survive the ordeal. 177 00:19:07,407 --> 00:19:11,958 Choosing an exposed site gives them a head start in the spring. 178 00:19:18,007 --> 00:19:22,797 Each year the ladybirds achieve the human impossible. 179 00:19:22,847 --> 00:19:26,283 Their forecasting methods remain a mystery. 180 00:19:30,927 --> 00:19:35,205 In ten years of study, the ladybird“s long-range forecasts 181 00:19:35,247 --> 00:19:37,238 have never failed. 182 00:19:45,207 --> 00:19:48,119 Migrating birds, such as the greylags, 183 00:19:48,167 --> 00:19:50,727 specialise in short-term forecasts. 184 00:19:50,767 --> 00:19:53,804 In autumn they set off when air pressure is falling. 185 00:19:53,847 --> 00:19:56,441 A north wind helps their journey. 186 00:19:57,807 --> 00:20:00,640 They possess a natural barometer in their inner ear 187 00:20:00,687 --> 00:20:03,804 sensitive to atmospheric changes. 188 00:20:04,687 --> 00:20:10,398 It also helps them sense altitude changes as small as three metres. 189 00:20:11,967 --> 00:20:14,435 By monitoring weather and altitude, 190 00:20:14,487 --> 00:20:16,876 birds can modify their flight plans 191 00:20:16,927 --> 00:20:20,044 to make the best of changing conditions. 192 00:20:35,847 --> 00:20:38,645 With favourable winds, the greylags can fly 193 00:20:38,687 --> 00:20:42,760 from Iceland to Scotland in as little as 12 hours. 194 00:20:45,927 --> 00:20:49,681 0ur ancient ancestors tried to understand the hidden forces 195 00:20:49,727 --> 00:20:51,922 that controlled nature. 196 00:20:53,127 --> 00:20:55,960 They built the stones of Callanish on the Isle of Lewis 197 00:20:56,007 --> 00:20:58,396 as a lunar calendar. 198 00:21:00,687 --> 00:21:03,155 Twice a day, the tides rise and fall 199 00:21:03,207 --> 00:21:06,961 in a rhythm driven by the moon“s gravitational pull. 200 00:21:08,327 --> 00:21:12,036 All life within coastal waters is affected. 201 00:21:13,207 --> 00:21:15,960 Even when removed from their tidal home, 202 00:21:16,007 --> 00:21:19,477 a body clock still keeps track of their home“s tidal cycle 203 00:21:19,527 --> 00:21:21,916 as long as they stay alive. 204 00:21:25,727 --> 00:21:29,436 Winkles in the seafood restaurant lie almost still, 205 00:21:29,487 --> 00:21:32,365 waiting for the time their home tide comes in. 206 00:21:34,767 --> 00:21:38,726 When water would have immersed the winkles, they become active, 207 00:21:38,767 --> 00:21:42,555 responding to a rhythm that has ceased to have any meaning. 208 00:21:46,487 --> 00:21:49,240 The timing of the tide varies with location, 209 00:21:49,287 --> 00:21:52,404 as does the activity of the inhabitants. 210 00:21:59,727 --> 00:22:02,924 Razor shells become active on an outgoing tide, 211 00:22:02,967 --> 00:22:06,482 squirting water to propel themselves 212 00:22:06,527 --> 00:22:09,485 under nonexistent sand. 213 00:22:22,127 --> 00:22:24,561 The moon“s pull may drive the tides, 214 00:22:24,607 --> 00:22:29,442 but its influence extends far beyond the intertidal zone. 215 00:22:37,167 --> 00:22:41,285 Scallops live in deeper water, but nevertheless have a body clock 216 00:22:41,327 --> 00:22:43,522 that predicts the tidal currents. 217 00:22:43,567 --> 00:22:46,639 They become active when the currents flow. 218 00:22:46,687 --> 00:22:49,440 ( # Jaunty piano ) 219 00:22:51,807 --> 00:22:54,037 Dancing helps them drift in the current, 220 00:22:54,087 --> 00:22:56,806 an easy way to find a new place to live. 221 00:23:15,007 --> 00:23:18,238 The moon affects more than just the tides. 222 00:23:18,287 --> 00:23:21,836 Many of its influences are still mysterious. 223 00:23:21,887 --> 00:23:24,959 The colour vision of freshwater guppies varies 224 00:23:25,007 --> 00:23:27,237 with the monthly lunar cycle. 225 00:23:27,287 --> 00:23:31,838 At the full moon, they“re more sensitive to yellow than violet. 226 00:23:31,887 --> 00:23:36,881 Two weeks later, at the new moon, they see violet better than yellow. 227 00:23:40,687 --> 00:23:45,124 Why this bizarre change of sensitivity occurs is puzzling. 228 00:23:48,607 --> 00:23:50,962 Early farmers built stone circles 229 00:23:51,007 --> 00:23:55,364 to try and make sense of the moon“s mysterious influence. 230 00:23:55,407 --> 00:24:00,276 Farmers always believed the moon affected crop ripening and yield. 231 00:24:00,327 --> 00:24:04,764 Until recently, science dismissed this as folklore. 232 00:24:05,407 --> 00:24:08,922 But recent research confirms plants do grow best 233 00:24:08,967 --> 00:24:10,764 around the full moon. 234 00:24:10,807 --> 00:24:13,765 Plant growth also shows a twice-daily cycle 235 00:24:13,807 --> 00:24:16,526 that coincides with the lunar one. 236 00:24:18,887 --> 00:24:22,721 Plant stems expand and contract with an internal tide 237 00:24:22,767 --> 00:24:26,123 on this 12-and-a-half-hour cycle. 238 00:24:26,167 --> 00:24:29,477 Potatoes are affected too, breathing in more oxygen 239 00:24:29,527 --> 00:24:32,246 at times of the moon“s greatest influence. 240 00:24:36,727 --> 00:24:40,561 How could lunar gravity affect a breathing potato? 241 00:24:41,927 --> 00:24:46,125 The moon“s orbit warps the earth“s magnetic field. 242 00:24:46,167 --> 00:24:51,116 Plants may somehow detect these twice-daily magnetic tides. 243 00:24:51,167 --> 00:24:54,318 Folklore, it seems, was right all along. 244 00:24:56,247 --> 00:24:58,238 The moon“s twice-monthly cycle 245 00:24:58,287 --> 00:25:01,085 also creates earth tides in the ground. 246 00:25:01,127 --> 00:25:03,925 This can precipitate earthquakes. 247 00:25:07,407 --> 00:25:11,878 Folklore suggests animals can predict these cataclysmic events. 248 00:25:11,927 --> 00:25:13,679 (Squeaking) 249 00:25:13,727 --> 00:25:16,241 Rats and other creatures have been observed 250 00:25:16,287 --> 00:25:18,847 carrying their brood to safety. 251 00:25:20,127 --> 00:25:24,245 In the Far East, zoo animals are monitored for unusual behaviour 252 00:25:24,287 --> 00:25:26,437 that might foretell a quake. 253 00:25:28,727 --> 00:25:32,686 Hippos are sensitive to sounds pitched below our hearing. 254 00:25:32,727 --> 00:25:34,877 Perhaps they hear rocks grinding 255 00:25:34,927 --> 00:25:37,885 under immense pressure deep below. 256 00:25:40,727 --> 00:25:42,718 (Squeaking) 257 00:25:46,087 --> 00:25:49,238 This infrasound is also heard by elephants. 258 00:25:49,287 --> 00:25:53,360 Their feet, sensitive to the distant stomps of other elephants, 259 00:25:53,407 --> 00:25:57,764 can detect pre-quake tremors too slight for us to notice. 260 00:25:57,807 --> 00:25:59,604 - (Snorting) - (Rumbling) 261 00:26:05,327 --> 00:26:09,036 Spiders, too, are sensitive to these micro-tremors, 262 00:26:09,087 --> 00:26:11,601 but ones vibrating at a higher frequency 263 00:26:11,647 --> 00:26:14,241 than those picked up by elephants. 264 00:26:16,407 --> 00:26:17,920 (Rumbling) 265 00:26:17,967 --> 00:26:23,200 The tarantula“s drum-like vibration detectors are buried in its legs. 266 00:26:23,247 --> 00:26:25,238 (Squeaking) 267 00:26:35,327 --> 00:26:39,002 Rocks under stress create high voltages. 268 00:26:39,047 --> 00:26:41,720 Static electricity reaching the surface 269 00:26:41,767 --> 00:26:44,235 can be felt by any furred animal. 270 00:26:49,447 --> 00:26:51,438 (Squeaking) 271 00:26:54,407 --> 00:26:57,126 (Rumbling) 272 00:26:57,167 --> 00:27:02,480 The earth“s magnetic field can warp, causing magnets to fail. 273 00:27:11,047 --> 00:27:12,844 In China, in the “80s, 274 00:27:12,887 --> 00:27:15,321 a million people were saved from an earthquake 275 00:27:15,367 --> 00:27:19,918 through the simple observation of strange animal behaviour. 276 00:27:29,327 --> 00:27:35,243 Just before a quake, a shift in the water table can drive animals above ground. 277 00:27:40,207 --> 00:27:41,640 (Trumpeting) 278 00:27:41,687 --> 00:27:44,759 Forces once hidden make their presence felt. 279 00:28:20,887 --> 00:28:26,757 0n our next journey, Supernatural explores the time warps of nature.