1 00:00:01,635 --> 00:00:03,237 NARRATOR: In the shadows of London, England, 2 00:00:03,237 --> 00:00:06,273 one of the world most successful species, 3 00:00:06,273 --> 00:00:12,212 the brown rat, stakes its claim. 4 00:00:12,212 --> 00:00:13,347 A continent away, 5 00:00:13,347 --> 00:00:16,483 the sea lions of San Francisco's Pier 39 6 00:00:16,483 --> 00:00:18,619 take a different tack, 7 00:00:18,619 --> 00:00:20,153 hauling out en masse 8 00:00:20,153 --> 00:00:23,523 in the light of day. 9 00:00:23,523 --> 00:00:26,260 And just outside Melbourne, Australia, 10 00:00:26,260 --> 00:00:29,096 fruit bats forced from their native home, 11 00:00:29,096 --> 00:00:32,833 take to the trees of a city park. 12 00:00:32,833 --> 00:00:34,534 In search of food and shelter, 13 00:00:34,534 --> 00:00:36,670 these uninvited guests 14 00:00:36,670 --> 00:00:40,507 use sheer numbers to secure new territory. 15 00:00:40,507 --> 00:00:42,342 Their very survival 16 00:00:42,342 --> 00:00:44,811 may depend on infesting a place 17 00:00:44,811 --> 00:00:50,350 where they're not welcome. 18 00:00:50,350 --> 00:00:52,552 NARRATOR: Inside the different realms 19 00:00:52,552 --> 00:00:56,189 of the wild kingdom, 20 00:00:56,189 --> 00:00:57,858 Members of a single species 21 00:00:57,858 --> 00:01:00,761 assemble in droves. 22 00:01:00,761 --> 00:01:02,663 And one flock, 23 00:01:02,663 --> 00:01:04,231 herd, 24 00:01:04,231 --> 00:01:05,599 or troop 25 00:01:05,599 --> 00:01:08,402 reigns supreme. 26 00:01:08,402 --> 00:01:18,445 These are the world's great 27 00:01:18,445 --> 00:01:24,384 These are the world's great 28 00:01:24,384 --> 00:01:26,586 NARRATOR: England is the most overcrowded 29 00:01:26,586 --> 00:01:34,227 major country in Europe. 30 00:01:34,227 --> 00:01:36,730 On average, over 1,000 people 31 00:01:36,730 --> 00:01:43,103 are squeezed into every square mile. 32 00:01:43,103 --> 00:01:48,542 That's over 50 million residents. 33 00:01:48,542 --> 00:01:50,544 And some say, 34 00:01:50,544 --> 00:01:57,384 there are just as many rats. 35 00:01:57,384 --> 00:01:58,719 On the outskirts of London, 36 00:01:58,719 --> 00:02:01,788 a derelict basement has been overrun 37 00:02:01,788 --> 00:02:04,324 with brown rats. 38 00:02:04,324 --> 00:02:07,394 A group of rats is called a mischief. 39 00:02:07,394 --> 00:02:09,096 It's a fitting term. 40 00:02:09,096 --> 00:02:11,164 At least 100 of these large rodents 41 00:02:11,164 --> 00:02:14,067 wreak havoc in the shadows of this building. 42 00:02:14,067 --> 00:02:22,342 It's a full-blown infestation. 43 00:02:22,342 --> 00:02:24,344 It was once believed that there was one rat 44 00:02:24,344 --> 00:02:29,783 for every person in the UK. 45 00:02:29,783 --> 00:02:31,451 Scientists suggest that it's more likely 46 00:02:31,451 --> 00:02:33,520 one for every six people, 47 00:02:33,520 --> 00:02:35,522 but that would still mean 48 00:02:35,522 --> 00:02:41,528 some 10 million rats. 49 00:02:44,264 --> 00:02:46,166 With the exception of Alberta, Canada, 50 00:02:46,166 --> 00:02:47,667 where extermination efforts 51 00:02:47,667 --> 00:02:51,138 have kept the province rat-free since the 1950s, 52 00:02:51,138 --> 00:03:05,318 rats live everywhere people do. 53 00:03:05,318 --> 00:03:08,422 After humans, this is the most successful mammal 54 00:03:08,422 --> 00:03:10,190 on the planet. 55 00:03:10,190 --> 00:03:11,558 Which makes it one of the world's 56 00:03:11,558 --> 00:03:23,737 greatest animal empires. 57 00:03:23,737 --> 00:03:26,339 The brown rat is also referred to 58 00:03:26,339 --> 00:03:31,311 as the Norway rat. 59 00:03:31,311 --> 00:03:33,380 British naturalists of the 18th century 60 00:03:33,380 --> 00:03:41,755 thought that it had migrated to England from Norway. 61 00:03:41,755 --> 00:03:43,857 But the species, in fact, 62 00:03:43,857 --> 00:03:46,259 originated on the plains of Asia 63 00:03:46,259 --> 00:03:52,632 in Northern China, and Mongolia. 64 00:03:52,632 --> 00:03:55,202 Some time in the middle ages, 65 00:03:55,202 --> 00:03:57,270 they began boarding ships, 66 00:03:57,270 --> 00:03:59,106 traveling far and wide, 67 00:03:59,106 --> 00:04:01,274 and spread to the four corners 68 00:04:01,274 --> 00:04:06,546 of the globe. 69 00:04:06,546 --> 00:04:09,249 By that time, black rats had already spread 70 00:04:09,249 --> 00:04:12,052 to Europe during the Roman Empire 71 00:04:12,052 --> 00:04:13,753 and had firmly cemented their reputation 72 00:04:13,753 --> 00:04:18,692 as household pests. 73 00:04:18,692 --> 00:04:21,795 But the larger, more aggressive brown rats 74 00:04:21,795 --> 00:04:23,330 eventually took over, 75 00:04:23,330 --> 00:04:29,402 displacing their relatives. 76 00:04:29,402 --> 00:04:33,740 Brown rats eat a wider variety of food. 77 00:04:33,740 --> 00:04:35,542 The transition from wooden buildings 78 00:04:35,542 --> 00:04:37,844 to brick and tile construction 79 00:04:37,844 --> 00:04:42,382 also favored brown rats. 80 00:04:42,382 --> 00:04:43,583 They're much better diggers 81 00:04:43,583 --> 00:04:45,852 and can tunnel under walls, 82 00:04:45,852 --> 00:04:54,227 and left black rats out in the cold. 83 00:04:54,227 --> 00:04:56,429 They also have very good hearing, 84 00:04:56,429 --> 00:05:00,033 a highly developed sense of smell, 85 00:05:00,033 --> 00:05:02,035 and can see ultraviolet lights 86 00:05:02,035 --> 00:05:06,072 that most animals cannot. 87 00:05:06,072 --> 00:05:08,041 But while there's much to admire 88 00:05:08,041 --> 00:05:09,509 about this super species, 89 00:05:09,509 --> 00:05:13,613 a rat is a very unwelcome guest. 90 00:05:13,613 --> 00:05:15,048 It was long believed that rats 91 00:05:15,048 --> 00:05:17,450 were responsible for the Black Death 92 00:05:17,450 --> 00:05:21,321 that devastated Europe in the 1300s. 93 00:05:21,321 --> 00:05:24,491 Evidence now suggests they may have been falsely accused. 94 00:05:24,491 --> 00:05:29,329 However, the stigma remains. 95 00:05:29,329 --> 00:05:32,165 Rats are known to transmit diseases, 96 00:05:32,165 --> 00:05:36,570 and they make a mess of basements and attics. 97 00:05:36,570 --> 00:05:38,838 So as these rodents multiply, 98 00:05:38,838 --> 00:05:42,209 so too do efforts to exterminate them. 99 00:05:42,209 --> 00:05:46,246 They are under near constant threat. 100 00:05:46,246 --> 00:05:48,481 Rats don't live long. The maximum life span 101 00:05:48,481 --> 00:05:52,652 of a brown rat is around three years. 102 00:05:52,652 --> 00:05:56,189 Most barely manage one. 103 00:05:56,189 --> 00:05:58,191 So for this animal empire, 104 00:05:58,191 --> 00:06:05,565 every day is truly a rat race. 105 00:06:05,565 --> 00:06:08,034 On the northern coast of California, 106 00:06:08,034 --> 00:06:10,103 the city of San Francisco 107 00:06:10,103 --> 00:06:12,505 is known for its historic icons 108 00:06:12,505 --> 00:06:15,075 like the Golden Gate Bridge 109 00:06:15,075 --> 00:06:17,410 and Alcatraz Prison. 110 00:06:17,410 --> 00:06:19,246 These landmarks, 111 00:06:19,246 --> 00:06:20,814 along with the region's moderate climate 112 00:06:20,814 --> 00:06:23,583 and easy-going pace, 113 00:06:23,583 --> 00:06:32,292 make it a popular place to live and visit. 114 00:06:32,292 --> 00:06:34,094 But it's not just an attractive place 115 00:06:34,094 --> 00:06:41,167 for residents and tourists. 116 00:06:41,167 --> 00:06:43,737 Pier 39, once a popular mooring spot 117 00:06:43,737 --> 00:06:45,739 on San Francisco Bay, 118 00:06:45,739 --> 00:06:52,812 is now infested with sea lions. 119 00:06:52,812 --> 00:06:54,648 Sea lions are part of a group 120 00:06:54,648 --> 00:06:56,483 known as "Pinnipeds", 121 00:06:56,483 --> 00:07:02,289 commonly known as seals. 122 00:07:02,289 --> 00:07:05,058 In fact, the clichéd circus seal, 123 00:07:05,058 --> 00:07:06,593 balancing a ball on its nose 124 00:07:06,593 --> 00:07:08,061 and jumping through hoops, 125 00:07:08,061 --> 00:07:13,667 is typically a California sea lion. 126 00:07:13,667 --> 00:07:15,769 Sea lions join fur seals 127 00:07:15,769 --> 00:07:18,605 to make up the family "Otariidae", 128 00:07:18,605 --> 00:07:22,642 also known as eared seals. 129 00:07:22,642 --> 00:07:28,782 Unlike other seals, they have external ear flaps. 130 00:07:28,782 --> 00:07:32,085 In addition, you can tell the difference 131 00:07:32,085 --> 00:07:34,454 by the sea lions' proportionately larger 132 00:07:34,454 --> 00:07:41,294 fore-flippers and pectoral muscles. 133 00:07:41,294 --> 00:07:44,197 Sea lions also have a long thin ridge of bone 134 00:07:44,197 --> 00:07:46,533 running along the skull, 135 00:07:46,533 --> 00:07:56,376 known as a sagittal crest. 136 00:07:56,376 --> 00:07:58,545 The range of the California sea lion 137 00:07:58,545 --> 00:08:00,780 stretches from Alaska in the north, 138 00:08:00,780 --> 00:08:03,049 to the Baja Peninsula, of Mexico 139 00:08:03,049 --> 00:08:05,618 in the south. 140 00:08:05,618 --> 00:08:08,154 California sea lions spend the summers 141 00:08:08,154 --> 00:08:10,323 breeding on the Channel Islands, 142 00:08:10,323 --> 00:08:12,559 just over 350 miles 143 00:08:12,559 --> 00:08:18,798 south of San Francisco. 144 00:08:18,798 --> 00:08:20,667 Once the breeding season is over, 145 00:08:20,667 --> 00:08:31,578 females stay close to the newborns on the islands. 146 00:08:31,578 --> 00:08:34,814 The males set out to the open ocean in search of food 147 00:08:34,814 --> 00:08:38,818 for as long as two weeks at a time. 148 00:08:38,818 --> 00:08:41,554 Between fishing trips, they need to rest, 149 00:08:41,554 --> 00:08:46,726 or "haul up" on shore. 150 00:08:46,726 --> 00:08:48,595 Many do so on the beaches 151 00:08:48,595 --> 00:08:53,466 of northern California. 152 00:08:53,466 --> 00:08:56,369 Large colonies are a fairly common sight 153 00:08:56,369 --> 00:08:57,804 along the coast, 154 00:08:57,804 --> 00:09:00,173 but less expected in the throng 155 00:09:00,173 --> 00:09:04,577 of a bustling metropolis. 156 00:09:04,577 --> 00:09:09,716 Pier 39 is in the heart of the city. 157 00:09:09,716 --> 00:09:11,418 It's smack dab in the middle 158 00:09:11,418 --> 00:09:14,554 of San Francisco's busy waterfront, 159 00:09:14,554 --> 00:09:17,123 sandwiched between restaurants, 160 00:09:17,123 --> 00:09:21,127 shops, and other attractions. 161 00:09:21,127 --> 00:09:23,196 Since 1989, 162 00:09:23,196 --> 00:09:26,099 sea lions have taken over 163 00:09:26,099 --> 00:09:30,069 Pier 39's K-Dock. 164 00:09:30,069 --> 00:09:33,273 The exact reason is unknown. 165 00:09:33,273 --> 00:09:36,109 It may be that it's simply a convenient rest stop 166 00:09:36,109 --> 00:09:38,278 between the breeding grounds to the south, 167 00:09:38,278 --> 00:09:41,214 and the foraging waters to the north. 168 00:09:41,214 --> 00:09:42,682 Whatever the reason, 169 00:09:42,682 --> 00:09:45,485 the arrival of these boisterous bulls 170 00:09:45,485 --> 00:09:47,654 has become a seasonal event each winter. 171 00:09:47,654 --> 00:09:50,690 Their presence shuts down the pier 172 00:09:50,690 --> 00:09:53,793 to boat traffic. 173 00:09:53,793 --> 00:09:55,695 And this hauling out has become 174 00:09:55,695 --> 00:10:05,738 an inner city infestation. 175 00:10:05,738 --> 00:10:12,645 an inner city infestation. 176 00:10:12,645 --> 00:10:15,482 Across the Pacific, 177 00:10:15,482 --> 00:10:18,318 on the south coast of Australia, 178 00:10:18,318 --> 00:10:19,719 the city of Geelong 179 00:10:19,719 --> 00:10:26,659 is an hour's drive southwest of Melbourne. 180 00:10:26,659 --> 00:10:29,529 Located on the waters of Port Phillips, 181 00:10:29,529 --> 00:10:30,697 Geelong is considered 182 00:10:30,697 --> 00:10:35,835 the gateway city for the region. 183 00:10:35,835 --> 00:10:38,838 And it is rapidly growing. 184 00:10:38,838 --> 00:10:45,144 Home to more than 180,000 people. 185 00:10:45,144 --> 00:10:47,180 This Melbourne suburb has been called 186 00:10:47,180 --> 00:10:52,418 one of Australia's most livable cities. 187 00:10:52,418 --> 00:10:55,321 And not just for humans. 188 00:10:55,321 --> 00:10:56,856 Geelong is also home 189 00:10:56,856 --> 00:11:10,403 to tens of thousands of bats! 190 00:11:10,403 --> 00:11:11,504 The grey-headed flying fox 191 00:11:11,504 --> 00:11:14,107 comes by its name honestly. 192 00:11:14,107 --> 00:11:20,280 It looks a lot like its namesake. 193 00:11:20,280 --> 00:11:22,782 But it is indeed a bat. 194 00:11:22,782 --> 00:11:26,686 And a big bat at that. 195 00:11:26,686 --> 00:11:29,222 The largest in Australia 196 00:11:29,222 --> 00:11:38,231 and one of the largest in the world. 197 00:11:38,231 --> 00:11:39,699 Bats are mammals, 198 00:11:39,699 --> 00:11:44,704 the only mammal capable of sustained flight. 199 00:11:44,704 --> 00:11:47,206 Bats belong to the order "Chiroptera", 200 00:11:47,206 --> 00:11:56,716 which literally means "hand-wing." 201 00:11:56,716 --> 00:11:59,252 There are two sub-orders. 202 00:11:59,252 --> 00:12:01,754 Most are familiar with the "micro bats", 203 00:12:01,754 --> 00:12:04,757 popularized by Halloween haunted houses, 204 00:12:04,757 --> 00:12:11,331 horror stories and the legend of Dracula 205 00:12:11,331 --> 00:12:13,333 Micro bats are smaller, 206 00:12:13,333 --> 00:12:15,335 only about the size of a mouse. 207 00:12:15,335 --> 00:12:20,640 They live in caves, and eat bugs. 208 00:12:20,640 --> 00:12:24,811 They also use "echolocation" to find their prey, 209 00:12:24,811 --> 00:12:26,446 calling out and using the echo 210 00:12:26,446 --> 00:12:32,819 that bounces back to navigate. 211 00:12:32,819 --> 00:12:35,321 The grey-headed flying fox, on the other hand, 212 00:12:35,321 --> 00:12:37,357 is a mega bat. 213 00:12:37,357 --> 00:12:40,793 It's not only larger, but it also has good eyesight 214 00:12:40,793 --> 00:12:46,499 and a superior sense of smell. 215 00:12:46,499 --> 00:12:53,506 This is their food of choice, fruit. 216 00:12:53,506 --> 00:13:00,480 In fact, they're commonly known as fruit bats. 217 00:13:00,480 --> 00:13:10,757 And instead of caves, they live in trees. 218 00:13:10,757 --> 00:13:14,560 Today, fruit bats only live in the tropical rainforests 219 00:13:14,560 --> 00:13:18,264 of eastern Australia. 220 00:13:18,264 --> 00:13:20,133 Decades ago, they were endemic 221 00:13:20,133 --> 00:13:26,305 to all southeastern Australia's forests. 222 00:13:26,305 --> 00:13:33,279 Numbers were in the millions. 223 00:13:33,279 --> 00:13:34,647 But as trees were cut down 224 00:13:34,647 --> 00:13:37,583 to make way for expanding cities and towns, 225 00:13:37,583 --> 00:13:39,185 factories and farms, 226 00:13:39,185 --> 00:13:43,289 development put added stress on fruit bat habitat. 227 00:13:43,289 --> 00:13:46,192 It is estimated that as much as 70% 228 00:13:46,192 --> 00:13:49,595 of some of the flying foxes' favored foraging sites 229 00:13:49,595 --> 00:13:52,699 have been lost since European settlement. 230 00:13:52,699 --> 00:13:55,768 As a result, there are now only between 231 00:13:55,768 --> 00:13:59,706 three and six hundred thousand in the range. 232 00:13:59,706 --> 00:14:04,077 They've simply run out of places to live. 233 00:14:04,077 --> 00:14:07,246 So in the late 1980s, the surviving fruit bats 234 00:14:07,246 --> 00:14:09,282 in the southeastern state of Victoria, 235 00:14:09,282 --> 00:14:11,784 made a move. 236 00:14:11,784 --> 00:14:14,120 They went from the wild woods, 237 00:14:14,120 --> 00:14:19,592 to Melbourne, and other nearby cities. 238 00:14:19,592 --> 00:14:21,761 Now, at least three permanent colonies 239 00:14:21,761 --> 00:14:23,229 make their home here, 240 00:14:23,229 --> 00:14:29,535 including this site, in Geelong's Eastern Park. 241 00:14:29,535 --> 00:14:31,637 It's hard to blame them. 242 00:14:31,637 --> 00:14:34,207 There's food and water nearby. 243 00:14:34,207 --> 00:14:35,341 It's warm in winter, 244 00:14:35,341 --> 00:14:38,711 and cool in summer. 245 00:14:38,711 --> 00:14:41,214 And the city's green spaces, like Eastern Park, 246 00:14:41,214 --> 00:14:50,223 offer protected trees that are ideal for roosting. 247 00:14:50,223 --> 00:14:52,592 As their forest homes continue to fall, 248 00:14:52,592 --> 00:14:54,427 more and more fruit bats 249 00:14:54,427 --> 00:14:58,564 move to the city looking for a roost. 250 00:14:58,564 --> 00:15:00,600 The Eastern Park colony 251 00:15:00,600 --> 00:15:05,471 has swelled to as many as 30,000. 252 00:15:05,471 --> 00:15:07,440 These big bats are not necessarily 253 00:15:07,440 --> 00:15:09,642 a welcome addition to the city. 254 00:15:09,642 --> 00:15:12,745 They can be intimidating and noisy. 255 00:15:12,745 --> 00:15:14,647 They damage other vegetation, 256 00:15:14,647 --> 00:15:19,385 and they are known to carry dangerous viruses. 257 00:15:19,385 --> 00:15:22,221 What was once an occasional stopover in the city 258 00:15:22,221 --> 00:15:25,825 has become an infestation. 259 00:15:25,825 --> 00:15:28,261 Bats in the belfry are one thing; 260 00:15:28,261 --> 00:15:29,462 bats on the golf course 261 00:15:29,462 --> 00:15:34,567 is something else altogether. 262 00:15:34,567 --> 00:15:36,736 But for the flying foxes themselves, 263 00:15:36,736 --> 00:15:38,337 the stakes are even higher. 264 00:15:38,337 --> 00:15:41,073 Their very survival 265 00:15:41,073 --> 00:15:43,276 depends on a peaceful coexistence 266 00:15:43,276 --> 00:15:57,857 with their human hosts. 267 00:15:57,857 --> 00:15:59,859 Great Britain's rat population 268 00:15:59,859 --> 00:16:02,328 doesn't have quite the same housing problem 269 00:16:02,328 --> 00:16:08,434 as the fruit bats. 270 00:16:08,434 --> 00:16:11,370 While Australia's bat-friendly forests are scarce, 271 00:16:11,370 --> 00:16:13,472 Britain offers more than enough 272 00:16:13,472 --> 00:16:16,442 suitable habitats for rats. 273 00:16:16,442 --> 00:16:19,312 There are plenty of sewers, garbage-filled alleyways, 274 00:16:19,312 --> 00:16:25,084 and bleak building basements to choose from. 275 00:16:25,084 --> 00:16:27,787 Rats will live pretty much anywhere 276 00:16:27,787 --> 00:16:31,257 they can find food. 277 00:16:31,257 --> 00:16:36,095 And they'll eat just about anything. 278 00:16:36,095 --> 00:16:39,265 Rats are true omnivores. 279 00:16:39,265 --> 00:16:41,534 They prefer grains and meat, 280 00:16:41,534 --> 00:16:44,770 but studies have shown that rats aren't picky. 281 00:16:44,770 --> 00:16:47,673 Scrambled eggs, macaroni and cheese, 282 00:16:47,673 --> 00:16:51,377 pet food, and even leftover fruit. 283 00:16:51,377 --> 00:16:57,450 They'll eat whatever happens to be around. 284 00:16:57,450 --> 00:16:59,552 Once rats identify a source of food, 285 00:16:59,552 --> 00:17:04,056 they first need to gain access. 286 00:17:04,056 --> 00:17:07,226 It doesn't take much to make an entrance. 287 00:17:07,226 --> 00:17:10,263 With a collapsible rib cage that's hinged at the spine, 288 00:17:10,263 --> 00:17:15,701 they can squeeze through cracks half their size. 289 00:17:15,701 --> 00:17:18,237 If a rat can get its head through a hole, 290 00:17:18,237 --> 00:17:21,040 the rest will follow. 291 00:17:21,040 --> 00:17:23,242 They can also enter through plumbing pipes, 292 00:17:23,242 --> 00:17:25,244 either by using their razor sharp claws 293 00:17:25,244 --> 00:17:28,714 and excellent balance to climb up the outside. 294 00:17:28,714 --> 00:17:31,417 Or they use their superior swimming skills 295 00:17:31,417 --> 00:17:33,552 on the inside. 296 00:17:33,552 --> 00:17:35,554 They are such good swimmers 297 00:17:35,554 --> 00:17:38,557 they can tread water for hours on end. 298 00:17:38,557 --> 00:17:41,227 And yes, they can even enter a building 299 00:17:41,227 --> 00:17:44,730 through a toilet. 300 00:17:44,730 --> 00:17:47,133 Once inside, rats start making their home 301 00:17:47,133 --> 00:17:50,136 by burrowing. 302 00:17:50,136 --> 00:17:52,705 In some cases, this means digging underground 303 00:17:52,705 --> 00:17:54,774 and making tunnels. 304 00:17:54,774 --> 00:17:57,543 In others, they collect nesting materials, 305 00:17:57,543 --> 00:18:01,047 insulation, straw, and any lightweight material 306 00:18:01,047 --> 00:18:08,220 they can use to create an enclosure. 307 00:18:08,220 --> 00:18:09,689 Burrows provide the pack 308 00:18:09,689 --> 00:18:14,293 with shelter and food storage, 309 00:18:14,293 --> 00:18:18,331 as well as safe, thermo-regulated nests. 310 00:18:18,331 --> 00:18:23,336 Each burrow has its own nest chamber. 311 00:18:23,336 --> 00:18:25,104 But rats may also share a burrow 312 00:18:25,104 --> 00:18:26,672 and raise their young together 313 00:18:26,672 --> 00:18:29,442 in a "communal nest". 314 00:18:29,442 --> 00:18:31,210 They connect their burrow to others 315 00:18:31,210 --> 00:18:35,114 made by their relatives. 316 00:18:35,114 --> 00:18:37,650 It's a system of one to six little burrows, 317 00:18:37,650 --> 00:18:39,585 not unlike families that chose to live 318 00:18:39,585 --> 00:18:43,456 in the same village. 319 00:18:43,456 --> 00:18:44,757 After a few days, 320 00:18:44,757 --> 00:18:47,393 a second entrance, called a bolt-hole, 321 00:18:47,393 --> 00:18:51,630 is added by digging from below. 322 00:18:51,630 --> 00:18:53,366 It serves as an emergency exit 323 00:18:53,366 --> 00:18:58,571 in case the burrow is invaded. 324 00:18:58,571 --> 00:19:00,239 Once the first burrow is finished, 325 00:19:00,239 --> 00:19:02,141 rats will continue to add on, 326 00:19:02,141 --> 00:19:04,043 using the same pattern, 327 00:19:04,043 --> 00:19:06,112 dig a tunnel, empty out a cavity, 328 00:19:06,112 --> 00:19:10,449 add a bolt-hole. 329 00:19:10,449 --> 00:19:11,751 Outside the burrow, 330 00:19:11,751 --> 00:19:13,786 brown rats tend to confine their movement 331 00:19:13,786 --> 00:19:18,724 to the same routes every day. 332 00:19:18,724 --> 00:19:23,596 Gradually, trails form on the surface. 333 00:19:23,596 --> 00:19:26,599 Rats don't like to go far. 334 00:19:26,599 --> 00:19:28,701 As long as food is available, 335 00:19:28,701 --> 00:19:30,603 they'll stay within 65 feet 336 00:19:30,603 --> 00:19:32,738 of their nest. 337 00:19:32,738 --> 00:19:39,745 It's a matter of avoiding risks. 338 00:19:39,745 --> 00:19:42,381 Even though these are incredibly adaptable creatures, 339 00:19:42,381 --> 00:19:45,051 they're also very vulnerable, 340 00:19:45,051 --> 00:19:51,223 especially outside the burrow. 341 00:19:51,223 --> 00:19:53,826 Predators, interspecies conflict, 342 00:19:53,826 --> 00:19:56,629 and the occasional run-in with an exterminator, 343 00:19:56,629 --> 00:19:58,330 can result in a rat colony 344 00:19:58,330 --> 00:20:05,171 having a mortality rate of 95%. 345 00:20:05,171 --> 00:20:10,176 Most rats don't make it past their first birthday. 346 00:20:10,176 --> 00:20:12,745 How is it then, that rats have maintained 347 00:20:12,745 --> 00:20:17,750 such a successful empire? 348 00:20:17,750 --> 00:20:19,151 In a word, 349 00:20:19,151 --> 00:20:25,524 In a word, breeding. 350 00:20:25,524 --> 00:20:29,128 Rats reach sexual maturity at an early age, 351 00:20:29,128 --> 00:20:30,296 at just five weeks old, 352 00:20:30,296 --> 00:20:33,532 and usually start breeding at two months. 353 00:20:33,532 --> 00:20:37,369 They can breed throughout the year. 354 00:20:37,369 --> 00:20:39,105 Mating behavior depends on the colony's 355 00:20:39,105 --> 00:20:40,739 population density. 356 00:20:40,739 --> 00:20:41,807 When numbers are low, 357 00:20:41,807 --> 00:20:49,348 one male rat will monopolize a burrow of females. 358 00:20:49,348 --> 00:20:51,283 It's a polygynous system 359 00:20:51,283 --> 00:20:53,619 where he mates with a number of females in his group, 360 00:20:53,619 --> 00:20:55,788 and only the members of his group. 361 00:20:55,788 --> 00:20:58,824 In this case, the male will defend his territory 362 00:20:58,824 --> 00:21:02,461 fiercely from other rats. 363 00:21:02,461 --> 00:21:05,064 He'll chase, bite and box, 364 00:21:05,064 --> 00:21:07,366 fluff up his hair, hiss, squeal, 365 00:21:07,366 --> 00:21:08,567 and wag his tail, 366 00:21:08,567 --> 00:21:09,835 anything to keep other males 367 00:21:09,835 --> 00:21:13,506 away from the females in the burrow. 368 00:21:13,506 --> 00:21:15,708 At higher population densities, 369 00:21:15,708 --> 00:21:17,409 males can no longer defend 370 00:21:17,409 --> 00:21:19,678 a burrow against rivals. 371 00:21:19,678 --> 00:21:23,782 There are simply too many. 372 00:21:23,782 --> 00:21:25,851 One alpha male rules the pack, 373 00:21:25,851 --> 00:21:29,688 but he can't control all the females. 374 00:21:29,688 --> 00:21:32,291 In this polygyandrous system, 375 00:21:32,291 --> 00:21:34,260 multiple males mate 376 00:21:34,260 --> 00:21:38,564 with multiple females. 377 00:21:38,564 --> 00:21:41,867 A female rat goes into heat, or estrus, 378 00:21:41,867 --> 00:21:45,638 every 4-5 days. 379 00:21:45,638 --> 00:21:48,707 The gestation period is only 21 days. 380 00:21:48,707 --> 00:21:50,242 Which means she can have about 381 00:21:50,242 --> 00:21:53,412 a dozen litters in one year. 382 00:21:53,412 --> 00:21:54,713 And each of those litters can have 383 00:21:54,713 --> 00:22:00,186 anywhere between 7 and 14 pups. 384 00:22:00,186 --> 00:22:05,157 Her offspring will start breeding within two months. 385 00:22:05,157 --> 00:22:06,492 And their offspring 386 00:22:06,492 --> 00:22:10,396 will be able to breed in another two months. 387 00:22:10,396 --> 00:22:12,331 That means, one mating couple 388 00:22:12,331 --> 00:22:15,701 can produce as many as 15,000 descendants 389 00:22:15,701 --> 00:22:20,539 in a year, if left to breed unchecked. 390 00:22:20,539 --> 00:22:24,076 At this rate, a few rats can quickly become 391 00:22:24,076 --> 00:22:25,844 an infestation. 392 00:22:25,844 --> 00:22:28,814 And an infestation can spell trouble. 393 00:22:28,814 --> 00:22:31,083 A crowded rat pack leads to 394 00:22:31,083 --> 00:22:34,286 increased competition and conflict. 395 00:22:34,286 --> 00:22:36,422 And can draw the unwanted attention 396 00:22:36,422 --> 00:22:48,400 of the local exterminator. 397 00:22:48,400 --> 00:22:50,536 Like rats and bats, 398 00:22:50,536 --> 00:22:56,475 California sea lions are motivated by hunger. 399 00:22:56,475 --> 00:22:59,411 The pod at San Francisco's Pier 39 400 00:22:59,411 --> 00:23:00,346 has figured out something 401 00:23:00,346 --> 00:23:04,483 their fellow migratory sea lions haven't, 402 00:23:04,483 --> 00:23:06,318 that the safe harbor of the pier 403 00:23:06,318 --> 00:23:11,824 provides them with just about everything they need. 404 00:23:11,824 --> 00:23:15,227 For one thing, there's plenty of fish in the sea. 405 00:23:15,227 --> 00:23:20,266 Or in this case, herring in the bay. 406 00:23:20,266 --> 00:23:21,734 Sea lions are binge feeders, 407 00:23:21,734 --> 00:23:26,739 eating all they can when food is plentiful. 408 00:23:26,739 --> 00:23:29,508 They'll eat anywhere between 10 to 40 pounds 409 00:23:29,508 --> 00:23:43,656 of food or more every day. 410 00:23:43,656 --> 00:23:45,291 In addition to the herring, 411 00:23:45,291 --> 00:23:49,828 they'll prey on some 50 species of marine life, 412 00:23:49,828 --> 00:23:52,164 including squids, octopuses, 413 00:23:52,164 --> 00:23:58,504 hake, salmon, and anchovy. 414 00:23:58,504 --> 00:24:00,172 They are excellent swimmers 415 00:24:00,172 --> 00:24:02,308 and can spend 15 hours at sea, 416 00:24:02,308 --> 00:24:06,278 diving up to 200 times. 417 00:24:06,278 --> 00:24:08,681 They hold their breath for up to 20 minutes 418 00:24:08,681 --> 00:24:16,755 and dive to depths of 1,000 feet. 419 00:24:16,755 --> 00:24:18,590 And they are speedy swimmers, 420 00:24:18,590 --> 00:24:27,633 clocking in at 22 miles per hour. 421 00:24:27,633 --> 00:24:29,702 While the Pier 39 sea lions 422 00:24:29,702 --> 00:24:32,237 may not have to work so hard for a meal, 423 00:24:32,237 --> 00:24:36,175 they still need a spot to haul out and rest. 424 00:24:36,175 --> 00:24:42,147 And the Pier provides a perfect accommodation. 425 00:24:42,147 --> 00:24:45,084 The docks rise and lower in the tide, 426 00:24:45,084 --> 00:24:47,252 saving them from having to move up and down 427 00:24:47,252 --> 00:24:50,823 from rocks on the shore. 428 00:24:50,823 --> 00:24:55,861 It's not unusual for them to sleep 8 to 12 hours a day. 429 00:24:55,861 --> 00:25:02,501 And they fast for several days at a time. 430 00:25:02,501 --> 00:25:06,171 Sea lions are very gregarious, social animals, 431 00:25:06,171 --> 00:25:15,814 so it's normal for large groups to haul out together. 432 00:25:15,814 --> 00:25:20,352 California sea lions can't sweat or pant. 433 00:25:20,352 --> 00:25:21,720 Their normal body temperature 434 00:25:21,720 --> 00:25:25,190 is about 100 degrees Fahrenheit. 435 00:25:25,190 --> 00:25:27,359 In order to regulate this temperature, 436 00:25:27,359 --> 00:25:31,463 they must move around in their environment. 437 00:25:31,463 --> 00:25:32,765 When it's cold, 438 00:25:32,765 --> 00:25:37,669 a sea lion will cozy up to others to stay warm. 439 00:25:37,669 --> 00:25:39,371 If it gets too hot, 440 00:25:39,371 --> 00:25:43,809 he'll lift a flipper or fan himself. 441 00:25:43,809 --> 00:25:46,545 Sea lion flippers have many capillaries 442 00:25:46,545 --> 00:25:48,347 that can be cooled off by the wind 443 00:25:48,347 --> 00:25:50,816 when sunbathing. 444 00:25:50,816 --> 00:25:57,723 Of course, he can also take a dip in the bay. 445 00:25:57,723 --> 00:26:01,126 The Pier also is also a place to haul out, 446 00:26:01,126 --> 00:26:04,797 providing protection, both from storms and predators, 447 00:26:04,797 --> 00:26:15,541 like sharks and orcas. 448 00:26:15,541 --> 00:26:17,810 It may seem like an ideal spot 449 00:26:17,810 --> 00:26:21,547 for these pinnipeds. 450 00:26:21,547 --> 00:26:25,250 But that means it's a popular one, too. 451 00:26:25,250 --> 00:26:28,153 On average, there can be up to 600 452 00:26:28,153 --> 00:26:31,056 hauled up on the pier. 453 00:26:31,056 --> 00:26:33,592 A record 1,700 454 00:26:33,592 --> 00:26:36,762 were counted in 2009. 455 00:26:36,762 --> 00:26:38,430 And there's not much room 456 00:26:38,430 --> 00:26:41,834 for a few hundred sea lions. 457 00:26:41,834 --> 00:26:45,437 These are massive marine mammals. 458 00:26:45,437 --> 00:26:46,839 A fully-grown male 459 00:26:46,839 --> 00:26:49,208 averages more than 660 pounds 460 00:26:49,208 --> 00:26:56,715 and is about eight feet long. 461 00:26:56,715 --> 00:27:01,253 This is a boisterous bunch, 462 00:27:01,253 --> 00:27:05,257 prone to bickering. 463 00:27:05,257 --> 00:27:07,493 When it comes to prime real estate, 464 00:27:07,493 --> 00:27:09,294 sea lions aren't afraid 465 00:27:09,294 --> 00:27:13,599 to fight over who got there first, 466 00:27:13,599 --> 00:27:23,642 and more importantly, who gets to stay. 467 00:27:23,642 --> 00:27:31,617 and more importantly, who gets to stay. 468 00:27:31,617 --> 00:27:37,756 Outside the city of Melbourne, Australia, 469 00:27:37,756 --> 00:27:40,225 a colony of grey-headed flying foxes 470 00:27:40,225 --> 00:27:42,294 has taken over the trees 471 00:27:42,294 --> 00:27:48,534 of Geelong's Eastern Park. 472 00:27:48,534 --> 00:27:50,269 These fruit bats have both summer 473 00:27:50,269 --> 00:27:57,309 and winter roosting camps in the trees. 474 00:27:57,309 --> 00:27:58,544 This summer camp, 475 00:27:58,544 --> 00:28:00,312 from September through round June, 476 00:28:00,312 --> 00:28:05,584 is their main camp. 477 00:28:05,584 --> 00:28:08,320 During the day, hundreds hang from the branches 478 00:28:08,320 --> 00:28:14,226 high up in the trees. 479 00:28:14,226 --> 00:28:20,198 There's a good reason they hang upside down. 480 00:28:20,198 --> 00:28:22,501 Bats are top heavy. 481 00:28:22,501 --> 00:28:24,736 The biggest bones and muscles 482 00:28:24,736 --> 00:28:30,776 are those used for flying. 483 00:28:30,776 --> 00:28:33,412 It's far more energy efficient to hang 484 00:28:33,412 --> 00:28:43,622 than to defy gravity and stand upright. 485 00:28:43,622 --> 00:28:46,091 It's during these long summer days 486 00:28:46,091 --> 00:28:50,262 that they mate. 487 00:28:50,262 --> 00:28:52,831 Males set up mating territories, 488 00:28:52,831 --> 00:28:58,136 generally three-and-a-half body-lengths along branches. 489 00:28:58,136 --> 00:29:03,609 Males fight for these territories. 490 00:29:03,609 --> 00:29:06,745 Those with the best locations, closer to the center, 491 00:29:06,745 --> 00:29:11,483 have access to more, and better, females. 492 00:29:11,483 --> 00:29:13,418 Males with lower-rent spots 493 00:29:13,418 --> 00:29:16,154 may have only one mate, 494 00:29:16,154 --> 00:29:20,492 or they're stuck being bachelors. 495 00:29:20,492 --> 00:29:22,327 At the beginning of the mating season, 496 00:29:22,327 --> 00:29:25,597 adult females move in towards the male territories 497 00:29:25,597 --> 00:29:29,368 where they become part of 'harems'. 498 00:29:29,368 --> 00:29:33,271 The harems consist of a male and up to five females, 499 00:29:33,271 --> 00:29:39,211 who come and go. 500 00:29:39,211 --> 00:29:44,750 It's the females who control the copulation process. 501 00:29:44,750 --> 00:29:47,085 Mating takes place during the day 502 00:29:47,085 --> 00:29:52,491 between March and May. 503 00:29:52,491 --> 00:29:55,127 After about six and a half months, 504 00:29:55,127 --> 00:29:59,364 babies, known as pups, are born. 505 00:29:59,364 --> 00:30:00,766 For the first three weeks, 506 00:30:00,766 --> 00:30:06,805 the pups are heavily dependent on their moms. 507 00:30:06,805 --> 00:30:10,609 Bat mothers provide milk and warmth for their babies, 508 00:30:10,609 --> 00:30:25,490 which cling to their moms for the first few weeks of life. 509 00:30:25,490 --> 00:30:27,526 As the day comes to a close, 510 00:30:27,526 --> 00:30:32,731 the adult bats ready to leave in search of food. 511 00:30:32,731 --> 00:30:34,700 Pups that are not yet three weeks old 512 00:30:34,700 --> 00:30:39,271 will cling to their mothers when they go foraging. 513 00:30:39,271 --> 00:30:40,872 Older pups remain in the roost 514 00:30:40,872 --> 00:30:45,844 until they are weaned at about six months. 515 00:30:45,844 --> 00:30:47,612 Bachelors and lactating females 516 00:30:47,612 --> 00:30:50,816 leave the roost first. 517 00:30:50,816 --> 00:30:53,685 Mating males wait and guard their harem 518 00:30:53,685 --> 00:30:55,854 until all have left. 519 00:30:55,854 --> 00:30:58,690 It's a catch-22. 520 00:30:58,690 --> 00:31:00,158 Those that leave earlier, 521 00:31:00,158 --> 00:31:04,796 have more time and light to work with. 522 00:31:04,796 --> 00:31:06,798 But this also makes them more vulnerable 523 00:31:06,798 --> 00:31:13,105 to predators, like hawks and eagles. 524 00:31:13,105 --> 00:31:15,474 For each fruit bat, it's a decision 525 00:31:15,474 --> 00:31:17,242 that could very well determine 526 00:31:17,242 --> 00:31:32,124 whether they will survive the night. 527 00:31:32,124 --> 00:31:35,193 In the dark recesses of this London basement, 528 00:31:35,193 --> 00:31:44,636 there's tension in the rat colony. 529 00:31:44,636 --> 00:31:46,438 There may have been plenty of space 530 00:31:46,438 --> 00:31:50,776 when the infestation began. 531 00:31:50,776 --> 00:31:54,446 But now, the rapidly expanding population 532 00:31:54,446 --> 00:32:00,051 is putting pressure on the over-crowded burrow. 533 00:32:00,051 --> 00:32:07,058 There's just not enough room. 534 00:32:07,058 --> 00:32:15,066 And now there are even more mouths to feed. 535 00:32:15,066 --> 00:32:16,401 Even though most rats 536 00:32:16,401 --> 00:32:19,738 won't live past the age of two or three, 537 00:32:19,738 --> 00:32:27,512 they're reproducing far faster than they're dying off. 538 00:32:27,512 --> 00:32:28,847 In just four months, 539 00:32:28,847 --> 00:32:40,859 this colony has grown by a factor of ten. 540 00:32:40,859 --> 00:32:47,732 Conflict is inevitable. 541 00:32:47,732 --> 00:32:52,838 Crowded rats turn aggressive. 542 00:32:52,838 --> 00:32:55,874 The alpha male goes on the offensive; 543 00:32:55,874 --> 00:33:04,115 he attacks and pushes out lower ranking males. 544 00:33:04,115 --> 00:33:06,318 It may seem like an extreme solution 545 00:33:06,318 --> 00:33:09,788 to the overcrowding problem, 546 00:33:09,788 --> 00:33:17,495 but it's a matter of maintaining the balance. 547 00:33:17,495 --> 00:33:19,364 If it gets too crowded, 548 00:33:19,364 --> 00:33:21,366 the strong will drive weaker members 549 00:33:21,366 --> 00:33:26,171 out of the colony. 550 00:33:26,171 --> 00:33:27,772 If the population declines, 551 00:33:27,772 --> 00:33:30,075 the remaining rats simply increase 552 00:33:30,075 --> 00:33:37,782 their reproductive rate to restore numbers. 553 00:33:37,782 --> 00:33:40,085 But it's not always one big rat race 554 00:33:40,085 --> 00:33:50,829 to see who stays and who goes. 555 00:33:50,829 --> 00:33:52,764 Studies have shown that rats 556 00:33:52,764 --> 00:34:00,272 also have the capacity to work together. 557 00:34:00,272 --> 00:34:05,043 They'll cooperate to get food. 558 00:34:05,043 --> 00:34:07,312 It's even suggested that a rat 559 00:34:07,312 --> 00:34:09,314 that has received help in the past 560 00:34:09,314 --> 00:34:11,716 is more likely to help another rat, 561 00:34:11,716 --> 00:34:18,390 even one that is unknown to him. 562 00:34:18,390 --> 00:34:19,324 In other words, 563 00:34:19,324 --> 00:34:22,527 cooperative rats don't just return favors, 564 00:34:22,527 --> 00:34:28,800 they also 'pay it forward.' 565 00:34:28,800 --> 00:34:38,743 Scientists call this "general reciprocation". 566 00:34:38,743 --> 00:34:40,745 It's the first time this behavior 567 00:34:40,745 --> 00:34:45,116 has been documented in nonhumans. 568 00:34:45,116 --> 00:34:47,619 And another example of how intelligent 569 00:34:47,619 --> 00:34:52,691 and adaptable these rodents are. 570 00:34:52,691 --> 00:34:54,492 And they must be. 571 00:34:54,492 --> 00:34:57,295 Though rats have the respect of researchers, 572 00:34:57,295 --> 00:35:00,332 and some even find a happy home as pets, 573 00:35:00,332 --> 00:35:04,636 they generally remain unwelcome house guests. 574 00:35:04,636 --> 00:35:12,444 Rats are under constant threat. 575 00:35:12,444 --> 00:35:14,713 And so, as the day breaks, 576 00:35:14,713 --> 00:35:16,681 the mischief settles safely 577 00:35:16,681 --> 00:35:23,688 back into the burrow. 578 00:35:23,688 --> 00:35:25,724 They spend the daylight hours 579 00:35:25,724 --> 00:35:30,595 hidden away as best they can. 580 00:35:30,595 --> 00:35:34,699 For some, there's work to be done storing food 581 00:35:34,699 --> 00:35:39,471 and maintaining the burrow. 582 00:35:39,471 --> 00:35:45,477 For others, it's time to sleep. 583 00:35:45,477 --> 00:35:52,117 They huddle together to conserve heat. 584 00:35:52,117 --> 00:35:54,719 New pups nestle together, depending on each other, 585 00:35:54,719 --> 00:36:01,626 and the heat from their mother. 586 00:36:01,626 --> 00:36:03,461 Once the young males are old enough, 587 00:36:03,461 --> 00:36:09,167 they will leave the nest and strike out on their own, 588 00:36:09,167 --> 00:36:14,639 setting off in search of new territory, 589 00:36:14,639 --> 00:36:18,343 and once again beginning the cycle of infestation, 590 00:36:18,343 --> 00:36:28,720 and expanding the empire. 591 00:36:28,720 --> 00:36:32,824 It's October in the city of San Francisco. 592 00:36:32,824 --> 00:36:43,268 There's no vacancy on Pier 39's K-Dock. 593 00:36:43,268 --> 00:36:46,071 At its busiest, the pier may be home 594 00:36:46,071 --> 00:36:55,146 for 500-600 sea lions. 595 00:36:55,146 --> 00:36:56,848 It can get awfully noisy when a few hundred 596 00:36:56,848 --> 00:37:06,224 large marine mammals haul out of the water. 597 00:37:06,224 --> 00:37:07,692 California sea lions 598 00:37:07,692 --> 00:37:10,695 are among the most vocal of all mammals. 599 00:37:10,695 --> 00:37:13,331 (sea lions bark) 600 00:37:13,331 --> 00:37:16,367 They bark, growl, and grunt loudly. 601 00:37:16,367 --> 00:37:20,738 (sea lions growl) 602 00:37:20,738 --> 00:37:23,374 (sea lions bark) 603 00:37:23,374 --> 00:37:24,809 During the mating season, 604 00:37:24,809 --> 00:37:28,079 males will bark incessantly at each other 605 00:37:28,079 --> 00:37:33,284 as they clash over territory. 606 00:37:33,284 --> 00:37:36,387 These fights frequently turn physical. 607 00:37:36,387 --> 00:37:39,224 Breeding bulls will do whatever it takes 608 00:37:39,224 --> 00:37:46,231 to establish dominance and claim a harem. 609 00:37:46,231 --> 00:37:47,665 Here on Pier 39, 610 00:37:47,665 --> 00:37:50,401 during the non-breeding season, 611 00:37:50,401 --> 00:37:51,836 it's the young submissive males 612 00:37:51,836 --> 00:37:57,509 that are most aggressive. 613 00:37:57,509 --> 00:37:59,210 Bulls usually reach 614 00:37:59,210 --> 00:38:04,616 10 years of age before they mate. 615 00:38:04,616 --> 00:38:05,683 When that time comes, 616 00:38:05,683 --> 00:38:07,685 they must be ready, 617 00:38:07,685 --> 00:38:14,492 so they train. 618 00:38:14,492 --> 00:38:18,563 It's every sea lion for himself. 619 00:38:18,563 --> 00:38:24,469 (sea lions growl and bark) 620 00:38:24,469 --> 00:38:26,337 While some scuffles at the pier 621 00:38:26,337 --> 00:38:28,706 are over favored spots on the docks, 622 00:38:28,706 --> 00:38:31,809 most fights are between these juvenile males, 623 00:38:31,809 --> 00:38:35,346 practicing the skills that they will need in the future. 624 00:38:35,346 --> 00:38:43,254 (sea lions bark and growl) 625 00:38:43,254 --> 00:38:45,156 They work their way up the hierarchy, 626 00:38:45,156 --> 00:38:47,492 taking part in regular bouts 627 00:38:47,492 --> 00:38:51,062 as they try to climb the social ladder. 628 00:38:51,062 --> 00:38:54,532 Only the strongest will get the chance to mate. 629 00:38:54,532 --> 00:39:02,106 (sea lions bark and growl) 630 00:39:02,106 --> 00:39:04,108 It's a rowdy affair. 631 00:39:04,108 --> 00:39:08,613 (sea lions bark and growl) 632 00:39:08,613 --> 00:39:10,648 They grapple and bite each other, 633 00:39:10,648 --> 00:39:13,585 and bump and thump their necks and chests. 634 00:39:13,585 --> 00:39:18,523 (sea lions bark and growl) 635 00:39:18,523 --> 00:39:21,459 Though injuries are common, fatalities are rare. 636 00:39:21,459 --> 00:39:27,165 (sea lions bark) 637 00:39:27,165 --> 00:39:30,101 A skirmish usually ends when one or the other 638 00:39:30,101 --> 00:39:35,406 is physically pushed away. 639 00:39:35,406 --> 00:39:42,614 Currently, the population of California sea lions is healthy. 640 00:39:42,614 --> 00:39:49,087 But it's not without its threats. 641 00:39:49,087 --> 00:39:51,623 Foraging adults can become entangled in fishing nets 642 00:39:51,623 --> 00:39:54,259 or plastic packaging materials, 643 00:39:54,259 --> 00:40:00,498 causing injury or even drowning. 644 00:40:00,498 --> 00:40:10,275 And the planet's changing climate is a growing concern. 645 00:40:10,275 --> 00:40:12,477 Declines in sea lion numbers 646 00:40:12,477 --> 00:40:14,812 have been linked to exceptionally warm currents 647 00:40:14,812 --> 00:40:21,586 that cause fish populations to shift. 648 00:40:21,586 --> 00:40:24,122 This can lead to poor nutrition, 649 00:40:24,122 --> 00:40:35,199 especially dangerous to pregnant and nursing females. 650 00:40:35,199 --> 00:40:36,834 These are increasing threats 651 00:40:36,834 --> 00:40:44,475 to the survival of the species. 652 00:40:44,475 --> 00:40:47,512 These young bulls face an uncertain future 653 00:40:47,512 --> 00:40:57,755 in a changing world. 654 00:40:57,755 --> 00:40:58,890 When the summer is over, 655 00:40:58,890 --> 00:41:02,060 they will join the other adults as they make their way 656 00:41:02,060 --> 00:41:05,296 from Pier 39, back to the breeding grounds 657 00:41:05,296 --> 00:41:14,772 off the Channel Islands. 658 00:41:14,772 --> 00:41:25,783 On the islands, their training will be put to the test. 659 00:41:25,783 --> 00:41:29,420 These young bulls will fight to win breeding rights, 660 00:41:29,420 --> 00:41:31,723 the chance to continue their lineage, 661 00:41:31,723 --> 00:41:41,766 and ensure a future for their empire. 662 00:41:41,766 --> 00:41:47,638 and ensure a future for their empire. 663 00:41:47,638 --> 00:41:50,274 Bat's wing bones are the same as those 664 00:41:50,274 --> 00:41:53,778 of a human arm and hand. 665 00:41:53,778 --> 00:41:59,150 But these bones are proportionately much longer. 666 00:41:59,150 --> 00:42:01,486 They're connected by a double membrane of skin 667 00:42:01,486 --> 00:42:05,757 that forms the wing. 668 00:42:05,757 --> 00:42:08,626 Different bat species have different wing shapes 669 00:42:08,626 --> 00:42:14,198 depending on where and how they eat. 670 00:42:14,198 --> 00:42:16,534 Flying foxes have an average wingspan 671 00:42:16,534 --> 00:42:21,539 of three feet. 672 00:42:21,539 --> 00:42:23,708 Flying foxes need their large wings 673 00:42:23,708 --> 00:42:26,377 to travel the relatively long distances 674 00:42:26,377 --> 00:42:39,690 to fruit-filled forests and fields. 675 00:42:39,690 --> 00:42:41,659 As day turns to dusk, 676 00:42:41,659 --> 00:42:44,495 the sky above Geelong's Eastern Park 677 00:42:44,495 --> 00:42:47,498 comes alive. 678 00:42:47,498 --> 00:42:49,834 The grey-headed flying foxes 679 00:42:49,834 --> 00:42:56,274 are setting off in search of food. 680 00:42:56,274 --> 00:42:59,577 When a wave of these large bats take flight, 681 00:42:59,577 --> 00:43:06,184 it quickly fills the sky. 682 00:43:06,184 --> 00:43:14,725 Their departure is an impressive sight. 683 00:43:14,725 --> 00:43:16,761 Most will travel an average radius 684 00:43:16,761 --> 00:43:21,666 of about 20 miles from the roost. 685 00:43:21,666 --> 00:43:28,606 Some will even go as far as 60 miles to find food. 686 00:43:28,606 --> 00:43:36,380 They travel at a speed of about 23 feet per second. 687 00:43:36,380 --> 00:43:38,449 If conditions are right, 688 00:43:38,449 --> 00:43:45,289 they can ride the wind and travel twice as fast. 689 00:43:45,289 --> 00:43:46,591 And they have to hurry 690 00:43:46,591 --> 00:43:52,129 if they're to be back before sun up. 691 00:43:52,129 --> 00:43:55,299 It's a myth that bats are blind. 692 00:43:55,299 --> 00:43:57,134 All bats can see, 693 00:43:57,134 --> 00:44:02,507 and see better than humans at night. 694 00:44:02,507 --> 00:44:08,546 But fruit bats have the best eyesight of all. 695 00:44:08,546 --> 00:44:10,248 They use their big eyes, 696 00:44:10,248 --> 00:44:12,650 along with a keen sense of smell, 697 00:44:12,650 --> 00:44:18,789 to locate food. 698 00:44:18,789 --> 00:44:21,292 Many of their food plants have blossoms 699 00:44:21,292 --> 00:44:24,829 that bats can see from above. 700 00:44:24,829 --> 00:44:28,432 They're on the lookout for the flowers of native trees, 701 00:44:28,432 --> 00:44:31,235 such as the many species of eucalyptus, 702 00:44:31,235 --> 00:44:35,606 as well as turpentines, and paperbarks. 703 00:44:35,606 --> 00:44:38,609 And of course, fruit. 704 00:44:38,609 --> 00:44:40,278 Bananas, mangos, 705 00:44:40,278 --> 00:44:41,712 dates, avocados, 706 00:44:41,712 --> 00:44:48,586 just about any kind of fruit will do. 707 00:44:48,586 --> 00:44:51,255 Far from the safety of the roost, 708 00:44:51,255 --> 00:44:54,091 these flying mammals are vulnerable. 709 00:44:54,091 --> 00:44:56,127 Out in the open air, 710 00:44:56,127 --> 00:44:58,796 predatory birds like hawks and eagles 711 00:44:58,796 --> 00:45:01,232 hunt the night sky. 712 00:45:01,232 --> 00:45:04,302 Weasels, snakes, and even cats 713 00:45:04,302 --> 00:45:12,443 prey upon fruit bats when they stop to rest or eat. 714 00:45:12,443 --> 00:45:19,717 But it's humans that present the greatest danger. 715 00:45:19,717 --> 00:45:21,452 Fruit farms are an attractive place 716 00:45:21,452 --> 00:45:27,658 for a grey headed flying fox to find a meal. 717 00:45:27,658 --> 00:45:31,195 Farmers have been known to trap and shoot bats 718 00:45:31,195 --> 00:45:36,200 to protect their crops 719 00:45:36,200 --> 00:45:37,668 Recent conservation efforts 720 00:45:37,668 --> 00:45:40,805 are trying to curb this trend. 721 00:45:40,805 --> 00:45:43,207 It's part of an increasing awareness 722 00:45:43,207 --> 00:45:45,476 of the important role that fruit bats play 723 00:45:45,476 --> 00:45:47,678 in the local ecosystem. 724 00:45:47,678 --> 00:45:49,680 The seeds they swallow 725 00:45:49,680 --> 00:45:51,816 move quickly through their system. 726 00:45:51,816 --> 00:45:54,485 They take only 20 minutes to digest, 727 00:45:54,485 --> 00:45:57,321 and are spread through the fruit bats' excretion. 728 00:45:57,321 --> 00:46:03,527 Bat guano is good for the environment. 729 00:46:03,527 --> 00:46:06,263 Increased clearing in the last two centuries 730 00:46:06,263 --> 00:46:12,336 has isolated scattered patches of forest. 731 00:46:12,336 --> 00:46:14,271 Flying foxes are able to move seeds 732 00:46:14,271 --> 00:46:17,608 over longer distances than insects and birds, 733 00:46:17,608 --> 00:46:21,646 linking these patches of native vegetation. 734 00:46:21,646 --> 00:46:24,815 In this way, grey-headed flying foxes 735 00:46:24,815 --> 00:46:26,817 can help rebuild the habitat 736 00:46:26,817 --> 00:46:30,254 that has been taken from them. 737 00:46:30,254 --> 00:46:33,424 But for now, as day breaks, 738 00:46:33,424 --> 00:46:36,260 they must return to the safety of the roost, 739 00:46:36,260 --> 00:46:38,062 to the Eastern Park trees 740 00:46:38,062 --> 00:46:49,507 and the city they have claimed as their home. 741 00:46:49,507 --> 00:46:53,444 NARRATOR: From the basements of Britain, 742 00:46:53,444 --> 00:46:58,249 to bustling San Francisco Bay, 743 00:46:58,249 --> 00:47:02,053 to the cities of southern Australia, 744 00:47:02,053 --> 00:47:04,622 every member of the wild kingdom 745 00:47:04,622 --> 00:47:08,125 depends on finding a suitable home. 746 00:47:08,125 --> 00:47:11,429 For rats, sea lions, and flying foxes, 747 00:47:11,429 --> 00:47:15,132 that means moving in where they may not be welcome. 748 00:47:15,132 --> 00:47:17,101 But whether invited or not, 749 00:47:17,101 --> 00:47:20,271 these species are simply struggling to survive, 750 00:47:20,271 --> 00:47:22,173 using strength in numbers 751 00:47:22,173 --> 00:47:25,209 to claim new territory 752 00:47:25,209 --> 00:47:26,744 and continue the legacy 753 00:47:26,744 --> 00:47:27,778 of their 754 00:47:27,778 --> 00:47:30,081 of their animal empires. 755 00:47:30,081 --> 00:47:40,124 ♪ THEME MUSIC ♪ 756 00:47:40,124 --> 00:47:54,438 ♪ THEME MUSIC ♪