1 00:00:35,887 --> 00:00:39,038 Morning in the rainforest of Panama. 2 00:00:45,407 --> 00:00:49,798 Capuchin monkeys are having a rather wasteful breakfast. 3 00:00:58,687 --> 00:01:03,886 Inside these nuts, there's a kernel that is very, very good eating, 4 00:01:04,047 --> 00:01:07,357 but it has such a hard shell, 5 00:01:07,527 --> 00:01:12,396 it's almost impossible to get at the kernel inside...even... 6 00:01:12,567 --> 00:01:15,161 ..if I hit it with a stone. 7 00:01:20,087 --> 00:01:24,524 Unbroken. So it's hard to believe, but nonetheless true, 8 00:01:24,687 --> 00:01:28,043 that one animal in these Central American forests 9 00:01:28,207 --> 00:01:31,995 can open these nuts with its bare teeth. 10 00:01:34,847 --> 00:01:37,884 But it's certainly not these monkeys. 11 00:01:38,047 --> 00:01:42,837 The best they can do is scrape off the thin, fleshy coating. 12 00:01:44,247 --> 00:01:47,637 The nut itself, they simply throw away. 13 00:01:50,367 --> 00:01:54,963 But another animal is listening for that telltale sound. 14 00:01:56,567 --> 00:01:58,523 (NUT DROPS) 15 00:02:00,967 --> 00:02:03,003 It's an agouti. 16 00:02:07,567 --> 00:02:12,561 (QUIETLY) The agouti is certainly no bigger or stronger than a monkey, 17 00:02:13,767 --> 00:02:18,124 but it has the right tools to deal with any nut... 18 00:02:21,367 --> 00:02:24,962 a pair of extremely strong and sharp front teeth 19 00:02:25,127 --> 00:02:28,915 that can cut through even the toughest casing. 20 00:02:32,087 --> 00:02:37,241 They belong to a large, successful group of mammals - the rodents. 21 00:02:37,407 --> 00:02:41,241 Rodents specialise in being able to chisel their way 22 00:02:41,407 --> 00:02:43,796 through almost anything. 23 00:02:53,967 --> 00:02:58,802 What is so special about an agouti's front teeth that enables them 24 00:02:58,967 --> 00:03:02,039 to cut a hole in the toughest of nuts? 25 00:03:04,407 --> 00:03:09,197 They have a layer of strong enamel, but only on the front surface. 26 00:03:09,367 --> 00:03:14,566 Behind it, the body of the tooth is made of a softer material: dentine. 27 00:03:14,727 --> 00:03:18,925 Gnawing wears down the dentine faster than the enamel, 28 00:03:19,087 --> 00:03:22,079 leaving an edge as sharp as a chisel. 29 00:03:22,247 --> 00:03:27,275 Unlike the front teeth of other mammals, a rodent's grow continuously, 30 00:03:27,447 --> 00:03:30,041 replacing what gets worn away. 31 00:03:33,807 --> 00:03:37,277 Armed with these formidable teeth, rodents have become 32 00:03:37,447 --> 00:03:42,043 the most successful and numerous of all mammals. 33 00:03:44,847 --> 00:03:48,044 The largest group are rats and mice. 34 00:03:48,207 --> 00:03:51,677 There are 1,300 species of those, 35 00:03:51,847 --> 00:03:55,556 and they're all accomplished stealers of seeds. 36 00:03:59,887 --> 00:04:04,563 Other rodents use their teeth to cut up vegetation. 37 00:04:04,727 --> 00:04:07,321 Some even tackle wood. 38 00:04:14,007 --> 00:04:18,444 The rodent body is very versatile and has evolved 39 00:04:18,607 --> 00:04:24,477 into an astonishing variety of shapes and sizes to suit many different lifestyles. 40 00:04:29,647 --> 00:04:33,356 So you might find a rodent almost anywhere. 41 00:04:35,487 --> 00:04:39,605 Some are amazingly nimble tree-climbers - the squirrels. 42 00:04:39,767 --> 00:04:46,718 They open cones and collect seeds that few other mammals can reach. 43 00:04:53,927 --> 00:04:59,399 Abert's squirrels use their teeth to nip off the tips of the branches 44 00:04:59,567 --> 00:05:04,721 of ponderosa pines, where the bark is particularly nutritious. 45 00:05:12,247 --> 00:05:14,681 This is a valuable food reserve 46 00:05:14,847 --> 00:05:19,318 if the pine cones run out during the long northern winters. 47 00:05:21,327 --> 00:05:24,319 Abert's squirrels are such specialised feeders, 48 00:05:24,487 --> 00:05:28,560 they can only survive where there are ponderosa pines. 49 00:05:28,727 --> 00:05:32,640 Most squirrels have more general tastes. 50 00:05:32,807 --> 00:05:36,322 High on their menus are often acorns. 51 00:05:42,887 --> 00:05:47,199 Oak trees produce a heavy crop of acorns each autumn. 52 00:05:52,207 --> 00:05:55,597 Good news for squirrels like these greys. 53 00:05:55,767 --> 00:06:00,557 They need to eat a great deal to fatten themselves up for winter. 54 00:06:08,687 --> 00:06:13,681 They must also bury some to eat later on, when times get hard. 55 00:06:19,967 --> 00:06:24,995 For squirrels here in the woodlands of the eastern US, in Virginia, 56 00:06:25,167 --> 00:06:27,635 things are not quite so simple. 57 00:06:27,807 --> 00:06:30,799 Here, there are two kind of oaks: 58 00:06:30,967 --> 00:06:36,087 red oaks and white oaks. Their acorns are very similar. 59 00:06:36,247 --> 00:06:41,037 This is the acorn of a white oak, and this a red oak. 60 00:06:41,207 --> 00:06:43,562 This one is slightly darker. 61 00:06:44,607 --> 00:06:49,203 But the acorns of the white oak germinate almost immediately, 62 00:06:49,367 --> 00:06:51,835 using up their food supply. 63 00:06:52,007 --> 00:06:56,603 The red oaks, on the other hand, don't germinate until next spring. 64 00:06:56,767 --> 00:07:00,555 The squirrels recognise the difference 65 00:07:00,727 --> 00:07:03,321 and treat them differently. 66 00:07:06,487 --> 00:07:10,685 When a squirrel finds a white acorn, it eats it immediately, 67 00:07:10,847 --> 00:07:14,840 because otherwise it would soon germinate. 68 00:07:20,687 --> 00:07:25,078 On the other hand, red acorns are almost always buried 69 00:07:25,247 --> 00:07:27,556 as a store for winter. 70 00:07:32,847 --> 00:07:38,160 Squirrels are colour blind, so can't recognise the difference by sight. 71 00:07:38,327 --> 00:07:41,797 The smell tells them which should be eaten 72 00:07:41,967 --> 00:07:45,357 and which should be buried for later. 73 00:07:45,527 --> 00:07:50,601 In some years, the white oaks produce their usual bonanza, 74 00:07:50,767 --> 00:07:55,158 while the red oaks provide hardly any at all. 75 00:07:55,327 --> 00:07:59,240 When this happens, the squirrels change tactics. 76 00:07:59,407 --> 00:08:03,400 You might think it's tucking in to a white acorn as usual, 77 00:08:03,567 --> 00:08:08,561 but, after only a quick nibble, it takes it away and buries it. 78 00:08:10,087 --> 00:08:12,885 What's it up to? 79 00:08:22,407 --> 00:08:28,846 It's neatly cut away the tip, beneath which lies the embryo of the seed. 80 00:08:29,007 --> 00:08:33,000 Once that has gone, the acorn will never germinate, 81 00:08:33,167 --> 00:08:38,036 but its food store will remain fresh all winter for the squirrel. 82 00:08:39,927 --> 00:08:43,522 So with dexterous paws to hold the acorn 83 00:08:43,687 --> 00:08:47,282 and sharp front teeth to cut out the embryo, 84 00:08:47,447 --> 00:08:49,836 the squirrels get the best value 85 00:08:50,007 --> 00:08:53,795 out of these apparently well-protected nuts. 86 00:08:59,087 --> 00:09:02,079 Seed-producing plants grow everywhere, 87 00:09:02,247 --> 00:09:07,241 so, potentially, seed-eating rodents can live everywhere, too. 88 00:09:07,407 --> 00:09:09,796 But there is one problem. 89 00:09:09,967 --> 00:09:14,165 All seeds are full of nutriment, but most are very small, 90 00:09:14,327 --> 00:09:17,319 like these from these desert plants. 91 00:09:17,487 --> 00:09:21,685 You need about 500 of these to make the food equivalent 92 00:09:21,847 --> 00:09:24,486 of a typical nut like an acorn. 93 00:09:27,487 --> 00:09:33,926 Rodents wanting to store the seeds from these face a transport problem. 94 00:09:34,087 --> 00:09:37,557 It'd be impractical to carry them one by one 95 00:09:37,727 --> 00:09:40,321 as squirrels carry acorns. 96 00:09:43,047 --> 00:09:48,246 Here in California's Mojave Desert, a rodent has solved that problem. 97 00:09:48,407 --> 00:09:51,205 Its burrows are all around me. 98 00:09:56,087 --> 00:09:59,875 Like most desert animals, the creature in this hole 99 00:10:00,047 --> 00:10:04,040 usually doesn't come out until dark, when it's cooler. 100 00:10:04,207 --> 00:10:07,563 If I scatter a few seeds around its entrance, 101 00:10:07,727 --> 00:10:12,118 maybe that will tempt him to come out a little earlier. 102 00:10:14,407 --> 00:10:17,126 Well, as it happens, it didn't. 103 00:10:17,287 --> 00:10:20,677 It wasn't until later, when the moon was up, 104 00:10:20,847 --> 00:10:24,078 that the burrow's owner showed itself. 105 00:10:27,167 --> 00:10:29,476 A kangaroo rat. 106 00:10:33,687 --> 00:10:39,205 It can carry hundreds of seeds in expandable cheek pouches. 107 00:10:40,567 --> 00:10:44,765 The pink toes poking out are those of its back legs, 108 00:10:44,927 --> 00:10:47,521 which support its whole body. 109 00:10:47,687 --> 00:10:50,679 That's why it's called a kangaroo rat. 110 00:10:50,847 --> 00:10:54,442 Its front legs are hidden beneath its chin, 111 00:10:54,607 --> 00:10:57,280 shovelling seeds into its mouth. 112 00:10:58,127 --> 00:11:01,517 Normally, it has to travel quite a long way 113 00:11:01,687 --> 00:11:04,838 to find enough seeds to fill its pouches. 114 00:11:05,007 --> 00:11:08,716 Tonight, because of this supply, its shopping bags 115 00:11:08,887 --> 00:11:11,879 are soon full enough to take back to its burrow. 116 00:11:19,687 --> 00:11:25,080 There we are. It covers them over with sand just to keep them safe. 117 00:11:33,887 --> 00:11:37,197 Its deep burrow is a relatively safe place. 118 00:11:37,367 --> 00:11:41,360 The rat sleeps here all day and much of the night. 119 00:11:41,527 --> 00:11:47,079 Even so, the slightest suspicious sound from outside will wake it. 120 00:11:47,247 --> 00:11:49,636 (WHOOSHING) 121 00:11:51,367 --> 00:11:56,760 A gopher snake crawls towards the burrow. It might find its way inside. 122 00:11:56,927 --> 00:11:59,646 It had better be seen off. 123 00:12:03,527 --> 00:12:06,519 Foot stamping is the first warning. 124 00:12:13,087 --> 00:12:15,396 That seems to have no effect. 125 00:12:15,567 --> 00:12:19,765 Perhaps kicking sand in its face will do the trick. 126 00:12:20,927 --> 00:12:23,919 The snake doesn't like that at all. 127 00:12:27,727 --> 00:12:30,446 Victory to the kangaroo rat. 128 00:12:33,607 --> 00:12:37,885 Seeds are not the only part of a plant that is edible. 129 00:12:38,047 --> 00:12:41,960 Some rodents, like marmots in the European Alps, 130 00:12:42,127 --> 00:12:44,516 eat the entire thing. 131 00:12:47,567 --> 00:12:50,365 And they fight over grazing rights. 132 00:12:56,687 --> 00:13:01,477 When they come out of their burrows in late spring after their winter sleep, 133 00:13:01,647 --> 00:13:06,357 they set about re-establishing their territorial boundaries. 134 00:13:08,287 --> 00:13:12,075 Calling and tail-flagging are only the preliminaries. 135 00:13:12,247 --> 00:13:14,442 (SQUEAKS) 136 00:13:14,607 --> 00:13:19,397 If that doesn't work, there's nothing for it but to go to battle. 137 00:13:25,967 --> 00:13:29,004 Senior males do most of the fighting, 138 00:13:29,167 --> 00:13:34,161 while their female partners guard the family burrow and watch. 139 00:13:47,407 --> 00:13:51,685 When a male wins a scrap, he marks the boundaries 140 00:13:51,847 --> 00:13:55,635 with scent from a gland on his cheek. 141 00:14:04,647 --> 00:14:06,763 Marmots form strong pair bonds, 142 00:14:06,927 --> 00:14:12,126 and the females usually only mate with their one permanent partner. 143 00:14:13,727 --> 00:14:17,925 By late spring, a marmot family consists of the adult pair 144 00:14:18,087 --> 00:14:22,285 with a few of last year's offspring, all of them females. 145 00:14:22,447 --> 00:14:26,201 Last year's males have already been chased away. 146 00:14:27,407 --> 00:14:30,205 Although daughters can stay, 147 00:14:30,367 --> 00:14:34,679 their mothers constantly beat them up, particularly in spring. 148 00:14:36,127 --> 00:14:42,396 They're persecuted so severely that, if any become pregnant, they abort. 149 00:14:42,567 --> 00:14:45,764 The reason for this merciless behaviour 150 00:14:45,927 --> 00:14:49,715 doesn't become apparent until later in the year. 151 00:14:53,207 --> 00:14:58,042 By mid-summer, relative peace has come to the mountainside. 152 00:14:58,207 --> 00:15:03,884 This season's babies emerge from the burrow for the first time. 153 00:15:04,687 --> 00:15:08,282 There are usually between four and six babies, 154 00:15:08,447 --> 00:15:14,317 and they immediately get down to the important business of grazing. 155 00:15:18,127 --> 00:15:22,723 Alpine summers are short, so marmots feed as fast as they can 156 00:15:22,887 --> 00:15:25,447 while they can. 157 00:15:25,607 --> 00:15:31,682 Incisors slice with ease through the tough stalks of flowers and grasses. 158 00:15:32,527 --> 00:15:37,123 The babies put on weight rapidly but, by the end of the summer, 159 00:15:37,287 --> 00:15:42,884 they still do not have fat reserves to match those of their parents. 160 00:15:43,047 --> 00:15:46,483 In autumn, the family start on their final harvest - 161 00:15:46,647 --> 00:15:51,562 hay to line the deep burrow where they will sleep through the winter. 162 00:16:20,967 --> 00:16:24,960 By October, the weather has turned really cold. 163 00:16:25,127 --> 00:16:27,880 In the burrow, the marmots' body temperature 164 00:16:28,047 --> 00:16:30,880 has dropped to two degrees centigrade. 165 00:16:31,047 --> 00:16:36,804 Their hearts are beating only two or three times a minute. They're hibernating. 166 00:16:36,967 --> 00:16:40,755 Their fat reserves will have to last them 167 00:16:40,927 --> 00:16:43,316 until the following April. 168 00:16:49,047 --> 00:16:52,164 They snuggle together to minimise heat loss. 169 00:16:52,327 --> 00:16:55,922 Youngsters are in the middle of the pile. 170 00:16:56,087 --> 00:17:01,798 With less bodyweight, they can't let their temperatures drop as low as the adults'. 171 00:17:04,927 --> 00:17:08,920 Thermal imaging shows that a baby, glowing orange, 172 00:17:09,087 --> 00:17:12,875 is warmer than the adults, which show green. 173 00:17:13,047 --> 00:17:18,041 The burrow, which registers blue, is well below freezing point. 174 00:17:19,687 --> 00:17:23,680 The adults couldn't keep more than one litter warm. 175 00:17:23,847 --> 00:17:30,446 That is why the dominant female made sure that none of her youngsters had babies. 176 00:17:35,407 --> 00:17:40,003 But hibernating isn't the only way to survive the winter in the mountains. 177 00:17:46,767 --> 00:17:52,399 In North America, winters can be just as severe as in the high Alps. 178 00:17:52,567 --> 00:17:56,560 Yet here, there's a rodent that manages to find food 179 00:17:56,727 --> 00:17:58,718 throughout the winter months. 180 00:17:58,887 --> 00:18:02,675 It does so with an extremely ingenious device: 181 00:18:02,847 --> 00:18:08,444 a refrigerator - a pool of deep, cold water like this. 182 00:18:08,607 --> 00:18:12,395 And over there is its builder and owner. 183 00:18:15,647 --> 00:18:19,845 A beaver, one of the family that lives here in this lake 184 00:18:20,007 --> 00:18:23,795 at the foot of the Teton Mountains in Wyoming. 185 00:18:27,967 --> 00:18:33,325 Beavers can get around on land, but they're most at home in water, 186 00:18:33,487 --> 00:18:36,479 where their webbed hind feet and large paddle-like tail 187 00:18:36,647 --> 00:18:41,641 make them powerful swimmers above and below the surface. 188 00:18:53,887 --> 00:19:00,759 Beavers feed on all kinds of vegetation and eat wood as well as leaves. 189 00:19:03,127 --> 00:19:05,846 They're accomplished engineers. 190 00:19:06,007 --> 00:19:10,398 This great pond is entirely their own creation. 191 00:19:13,767 --> 00:19:19,558 Only a few years ago, this shallow stream flowed down the valley, 192 00:19:19,727 --> 00:19:23,925 then a family of beavers moved in and built a dam. 193 00:19:27,687 --> 00:19:30,884 The main body of it is built of boulders. 194 00:19:31,047 --> 00:19:34,517 On the downstream side, it's been lined with logs, 195 00:19:34,687 --> 00:19:36,837 some big and quite heavy. 196 00:19:37,007 --> 00:19:41,205 On this side, it's been packed with mud and vegetation. 197 00:19:41,367 --> 00:19:45,963 It's been built so accurately that it is, to within a few inches, 198 00:19:46,127 --> 00:19:50,598 horizontal across its entire length of about 150 yards 199 00:19:50,767 --> 00:19:53,235 from one side to the other. 200 00:19:53,407 --> 00:19:58,401 The lake it's created stretches upstream for almost a mile. 201 00:20:07,607 --> 00:20:12,601 So important is their dam to them that, if they detect any leak, 202 00:20:12,767 --> 00:20:18,364 usually by hearing trickling water, they start repair work immediately. 203 00:20:33,287 --> 00:20:36,484 Mud is needed as well as logs. 204 00:20:49,487 --> 00:20:54,641 The repair team will labour away until the leak is fully repaired. 205 00:20:58,687 --> 00:21:03,886 Maintaining the water at a high level brings beavers several advantages. 206 00:21:04,047 --> 00:21:09,644 It floods the surrounding woodlands and so enables them to swim safely 207 00:21:09,807 --> 00:21:12,605 to their main source of food. 208 00:21:18,287 --> 00:21:22,485 They increase the distance they can swim by digging channels 209 00:21:22,647 --> 00:21:26,435 that lead into the very heart of the woodland. 210 00:21:34,487 --> 00:21:37,206 Here they can use their sharp incisors 211 00:21:37,367 --> 00:21:41,360 to strip off the bark from a fallen tree and nibble at it, 212 00:21:41,527 --> 00:21:44,917 while being close enough to water to slip away 213 00:21:45,087 --> 00:21:48,557 should a bear or a mountain lion turn up. 214 00:22:18,607 --> 00:22:23,397 Their network of channels enables them to ferry whole branches 215 00:22:23,567 --> 00:22:25,558 back to their pond. 216 00:22:42,487 --> 00:22:44,876 Where the water is deepest, 217 00:22:45,047 --> 00:22:49,438 they dive down and push each branch firmly into the mud 218 00:22:49,607 --> 00:22:51,598 at the bottom. 219 00:22:52,607 --> 00:22:56,646 This is the beavers' fridge, where vegetation will keep fresh 220 00:22:56,807 --> 00:23:01,403 through the long winter when the pond is covered with ice. 221 00:23:09,207 --> 00:23:12,199 Stocking the fridge takes a lot of work. 222 00:23:12,367 --> 00:23:15,564 The beavers are at their busiest in autumn. 223 00:24:07,247 --> 00:24:12,480 At one side of the lake stands their lodge, a fortress of branches and boulders 224 00:24:12,647 --> 00:24:17,004 that's so strong that not even a bear could break into it. 225 00:24:17,247 --> 00:24:20,557 The only entrance is through underwater tunnels. 226 00:24:20,727 --> 00:24:25,323 The beavers take refuge here whenever they are alarmed. 227 00:24:35,207 --> 00:24:38,005 That was a warning signal 228 00:24:38,167 --> 00:24:41,557 to say that danger was around, that's to say - me. 229 00:24:41,727 --> 00:24:45,322 Now I may not see the beavers for some time. 230 00:24:45,487 --> 00:24:50,607 They can stay underwater for five minutes, up to 15 if they need to. 231 00:24:50,767 --> 00:24:53,759 They can get back to their lodge 232 00:24:53,927 --> 00:24:57,636 without putting their head above the surface for a second. 233 00:25:01,807 --> 00:25:05,800 Most lodges have at least two different entrances. 234 00:25:13,727 --> 00:25:15,957 By October, winter is underway. 235 00:25:16,127 --> 00:25:20,917 Marmots would now be hibernating, but the beavers are still active, 236 00:25:21,087 --> 00:25:25,399 and will remain that way throughout the winter. 237 00:25:27,127 --> 00:25:29,846 Even when the pond ices over, 238 00:25:30,007 --> 00:25:35,445 they can still swim under the ice to get back and forth to their lodge. 239 00:25:36,447 --> 00:25:40,042 No one knew what went on inside the lodge in winter, 240 00:25:40,207 --> 00:25:44,678 so when the beavers were away, we installed infrared cameras 241 00:25:44,847 --> 00:25:47,236 in order to find out. 242 00:25:51,327 --> 00:25:56,685 A branch from the fridge is brought back for the whole family to feed on. 243 00:26:02,247 --> 00:26:04,238 And another. 244 00:26:08,447 --> 00:26:11,837 No wonder they don't need to hibernate. 245 00:26:12,007 --> 00:26:15,204 The lodge is warm and safe even in mid-winter. 246 00:26:15,367 --> 00:26:19,565 The only sign of activity in the snug home beneath the snow 247 00:26:19,727 --> 00:26:23,436 is hot air rising from the vent at the top. 248 00:26:31,127 --> 00:26:35,518 Inside, our cameras catch a glimpse of what, at first sight, 249 00:26:35,687 --> 00:26:38,679 looks like a very small beaver. 250 00:26:40,407 --> 00:26:44,878 It's a muskrat. There are a pair of them in here. 251 00:26:45,047 --> 00:26:47,766 This is a new observation. 252 00:26:48,767 --> 00:26:51,565 Do the beavers know, in the dark, 253 00:26:51,727 --> 00:26:54,685 that there are strangers among them? 254 00:27:00,487 --> 00:27:05,561 The muskrats regularly left the lodge to forage under the ice. 255 00:27:07,247 --> 00:27:13,243 On several occasions, they returned a few minutes later with fresh reeds. 256 00:27:14,687 --> 00:27:16,996 Perhaps they're paying rent 257 00:27:17,167 --> 00:27:20,955 by regularly providing fresh bedding for the lodge. 258 00:27:31,207 --> 00:27:33,926 Maybe that is why the beavers accept them 259 00:27:34,087 --> 00:27:37,079 and even allow them to share their food. 260 00:27:49,327 --> 00:27:54,526 Our infrared lights, however, are no longer welcome, it seems. 261 00:27:57,407 --> 00:28:00,797 A lodge makes a safe home for a beaver. 262 00:28:00,967 --> 00:28:05,518 Other rodents defend themselves more actively, and one is positively dangerous. 263 00:28:08,727 --> 00:28:12,686 Darkness provides one of the best forms of defence, 264 00:28:12,847 --> 00:28:15,315 and it's very dark right now. 265 00:28:15,487 --> 00:28:18,877 The only reason you can see me 266 00:28:19,047 --> 00:28:22,278 is that we're using a starlight camera. 267 00:28:22,447 --> 00:28:26,918 Many rodents only come out under cover of darkness. 268 00:28:27,087 --> 00:28:32,878 That applies even to one of the most ferocious, well-armed of all rodents. 269 00:28:33,047 --> 00:28:36,642 I think there could be one around here. 270 00:28:53,287 --> 00:28:58,680 (QUIETLY) And there it is, and what a formidable sight - 271 00:28:58,847 --> 00:29:01,839 an African crested porcupine. 272 00:29:02,847 --> 00:29:08,240 It seems to have found something to eat underneath that spiny bush. 273 00:29:09,367 --> 00:29:13,155 Most of the time, those quills would be lying flat. 274 00:29:13,327 --> 00:29:19,323 The fact they're half erect is a sign that it's not happy that I'm so close. 275 00:29:31,367 --> 00:29:34,962 Those long quills are very sharp, 276 00:29:35,127 --> 00:29:38,915 and I'm quite sure it knows how to use them. 277 00:29:40,607 --> 00:29:46,079 It's turning its back on me, but that's not because it's about to run away. 278 00:29:46,247 --> 00:29:51,526 If it gets really angry, it will attack by suddenly sprinting backwards. 279 00:29:52,567 --> 00:29:54,558 And it's off. 280 00:29:56,207 --> 00:29:59,995 That's not the sort of thing you want to stumble into 281 00:30:00,167 --> 00:30:02,886 in the middle of the African night. 282 00:30:09,647 --> 00:30:14,118 They feed mainly on roots and tubers, but they're big animals 283 00:30:14,287 --> 00:30:19,281 and to find enough to eat, they travel long distances across open savannah. 284 00:30:19,447 --> 00:30:24,965 And that means they have to be prepared to take on all comers. 285 00:30:28,847 --> 00:30:33,125 This young leopard has probably never been close to a porcupine. 286 00:30:33,287 --> 00:30:37,200 He doesn't realise it would be dangerous to interfere with it. 287 00:30:48,487 --> 00:30:53,959 The porcupine seems to have total confidence in its armoury. 288 00:30:57,087 --> 00:31:03,083 If it's not careful, that naive leopard will end up with a face full of quills. 289 00:31:31,287 --> 00:31:35,121 And the porcupine goes back to digging for food. 290 00:31:35,287 --> 00:31:37,755 There's confidence for you. 291 00:31:41,287 --> 00:31:45,166 Belding's ground squirrels don't have that kind of nerve. 292 00:31:45,327 --> 00:31:49,400 They live in California and burrow close to one another, 293 00:31:49,567 --> 00:31:54,960 so there's always plenty of watchers to give warning of any danger. 294 00:31:55,127 --> 00:32:00,485 This is important during the summer when there are babies about. 295 00:32:05,967 --> 00:32:09,323 There are always at least one or two adults on watch nearby, 296 00:32:09,487 --> 00:32:12,877 so that the young can feed in relative safety. 297 00:32:13,047 --> 00:32:17,518 Only the females care for the young. They're nearly all related. 298 00:32:17,687 --> 00:32:22,078 Mothers, sisters and daughters look after nephews and nieces 299 00:32:22,247 --> 00:32:26,035 as carefully as they do their own offspring. 300 00:32:35,167 --> 00:32:39,763 When a guard spots a potential predator such as an eagle, 301 00:32:39,927 --> 00:32:41,963 she sounds a warning. 302 00:32:42,967 --> 00:32:47,438 Those trills mean ''Danger seen, but evasive action not needed''. 303 00:32:47,607 --> 00:32:49,199 (SQUEAKS) 304 00:32:52,087 --> 00:32:54,760 A bobcat. Another warning. 305 00:32:54,927 --> 00:32:57,680 (SQUEAKS) 306 00:33:01,527 --> 00:33:05,156 Each female is trying to keep the enemy in view 307 00:33:05,327 --> 00:33:08,637 so it doesn't catch them by surprise. 308 00:33:12,847 --> 00:33:18,080 The bobcat is getting closer. Now the warning will change. 309 00:33:20,087 --> 00:33:23,079 That means ''Run for it!'' 310 00:33:46,287 --> 00:33:50,166 Another small rodent that would make a tasty meal 311 00:33:50,327 --> 00:33:53,125 lives here in the arid north of Kenya. 312 00:33:53,287 --> 00:33:57,075 There are dozens within a few yards of me. 313 00:33:57,807 --> 00:34:01,402 But this one has adopted the safest strategy of all - 314 00:34:01,567 --> 00:34:05,606 to spend nearly all of its time below ground. 315 00:34:11,687 --> 00:34:16,044 And this is all that most people will ever see of it. 316 00:34:16,207 --> 00:34:18,357 A naked mole rat. 317 00:34:20,767 --> 00:34:23,235 They use their teeth for digging. 318 00:34:23,407 --> 00:34:26,399 Uniquely, their lips close behind the teeth. 319 00:34:26,567 --> 00:34:30,719 That stops earth getting into their mouth. 320 00:34:30,887 --> 00:34:34,641 With this superb equipment, they dig a network of tunnels 321 00:34:34,807 --> 00:34:36,798 radiating from a central chamber 322 00:34:36,967 --> 00:34:40,801 where the colony gathers and the babies are kept. 323 00:34:40,967 --> 00:34:46,360 All the babies are produced by one big female, the colony's founder. 324 00:34:46,527 --> 00:34:49,644 The rest, and there may be as many as 100, 325 00:34:49,807 --> 00:34:52,844 are her children and none will breed here 326 00:34:53,007 --> 00:34:55,760 as long as their mother is alive. 327 00:34:55,927 --> 00:35:00,921 Their job is to tunnel away, searching for tubers and roots. 328 00:35:01,087 --> 00:35:04,796 By doing that, they create a vast network of tunnels 329 00:35:04,967 --> 00:35:09,358 stretching for hundreds of yards under the African plains. 330 00:35:09,527 --> 00:35:12,837 Above ground, it's hard to find any plants 331 00:35:13,007 --> 00:35:17,000 that might provide mole rats with an underground meal. 332 00:35:17,167 --> 00:35:21,957 Mostly there's just dry grass and the odd acacia seedling. 333 00:35:26,007 --> 00:35:30,603 When mole rats meet, they assess one another's status with a sniff. 334 00:35:30,767 --> 00:35:35,158 The junior one has to pass underneath the senior one. 335 00:35:45,287 --> 00:35:50,998 Being blind, they're just as happy travelling backwards as forwards. 336 00:35:55,967 --> 00:36:00,757 I'm about a quarter of a mile from where I saw the mole rats digging. 337 00:36:00,927 --> 00:36:03,919 This is the plant I've been looking for. 338 00:36:04,087 --> 00:36:08,080 Now, in the dry season, it's nothing more than a curly stem 339 00:36:08,247 --> 00:36:10,238 and a few withered leaves, 340 00:36:10,407 --> 00:36:14,400 but beneath the ground here, there's treasure. 341 00:36:31,167 --> 00:36:33,158 And here it is. 342 00:36:33,327 --> 00:36:37,525 Tubers like this are few and far between around here. 343 00:36:37,687 --> 00:36:43,956 It's a matter of pure chance as to whether the mole rats bump into one. 344 00:36:44,287 --> 00:36:48,280 So mole rat colonies must have several dozen workers, 345 00:36:48,447 --> 00:36:50,642 but if they do find one like this, 346 00:36:50,807 --> 00:36:54,880 it could sustain the colony for two or three weeks. 347 00:37:07,487 --> 00:37:11,480 Their sharp incisors cut into the tough tuber. 348 00:37:11,647 --> 00:37:15,640 Some of it, the lucky finders will eat on the spot. 349 00:37:20,847 --> 00:37:25,967 They drag back lumps to the central chamber to be shared by the colony. 350 00:37:30,047 --> 00:37:34,086 This arrangement, where workers are sterile and labour away 351 00:37:34,247 --> 00:37:39,037 to support their mother, is also the basis for the colonies of bees and ants. 352 00:37:39,207 --> 00:37:42,916 But naked mole rats are the only mammals 353 00:37:43,087 --> 00:37:45,476 that have adopted it. 354 00:37:53,647 --> 00:37:57,845 Although those long chiselled front teeth are rodent hallmarks, 355 00:37:58,007 --> 00:38:03,240 rodents are also famous for reproducing with extraordinary rapidity. 356 00:38:03,407 --> 00:38:05,398 Mole rats certainly do that, 357 00:38:05,567 --> 00:38:11,437 but the most prolific members of the whole family are the mice. 358 00:38:14,447 --> 00:38:18,440 Tiny harvest mice produce babies in a carefully woven nest 359 00:38:18,607 --> 00:38:22,600 among the stems of reeds or tall grasses. 360 00:38:30,847 --> 00:38:33,441 Litters of up to eight babies 361 00:38:33,647 --> 00:38:37,959 fed on their mother's rich milk mature in only a few weeks. 362 00:38:42,687 --> 00:38:48,239 Each pair can produce three litters, nearly 30 young, in a single season, 363 00:38:48,407 --> 00:38:53,197 provided that the adults can find enough seeds to feed on. 364 00:39:02,727 --> 00:39:06,117 Youngsters leave the nest at only two weeks old 365 00:39:06,287 --> 00:39:08,960 and start searching for food. 366 00:39:14,687 --> 00:39:19,681 To begin with, they're not nearly as agile as their parents. 367 00:39:32,967 --> 00:39:38,166 In fact, sometimes they seem quite unsure about where they can safely tread. 368 00:39:49,207 --> 00:39:52,040 These little creatures have lived in our cornfields, 369 00:39:52,207 --> 00:39:56,678 taking a small proportion of our crops, ever since farming began. 370 00:39:56,847 --> 00:39:59,839 Usually they were only visible when crops were gathered, 371 00:40:00,007 --> 00:40:03,317 which is why they were called harvest mice. 372 00:40:05,047 --> 00:40:09,040 Even after harvesting, there's still the spilled grain to feed on. 373 00:40:09,207 --> 00:40:14,201 In the vast wheat belt of Australia, a different mouse takes advantage 374 00:40:14,367 --> 00:40:17,040 of this plentiful supply of food, 375 00:40:17,207 --> 00:40:21,200 digging burrows along the edge of the sandy fields. 376 00:40:25,127 --> 00:40:29,837 These are common house mice, the most prolific breeders of all. 377 00:40:30,007 --> 00:40:34,717 Each new female can become pregnant at only five weeks old. 378 00:40:34,887 --> 00:40:40,484 If there's a good supply of grain, she will breed every month or so. 379 00:40:43,287 --> 00:40:46,996 In some years, if all the grain gets eaten, 380 00:40:47,167 --> 00:40:51,240 the mice head for the nearest farm buildings to look for food. 381 00:40:54,807 --> 00:41:00,996 As they leave the stripped fields, it's clear how many have been feasting. 382 00:41:11,487 --> 00:41:17,084 Once they do find their way into a grain store, they become a plague. 383 00:41:34,567 --> 00:41:40,802 When they finish the grain, their numbers will fall as quickly as they rose. 384 00:41:44,247 --> 00:41:49,446 On the flat, windswept plains of Patagonia lives a much larger rodent, 385 00:41:49,607 --> 00:41:52,075 with a more leisured system of breeding. 386 00:41:52,247 --> 00:41:54,681 These are Patagonian cavies or maras. 387 00:41:54,847 --> 00:41:57,998 Although this litter appears very large, 388 00:41:58,167 --> 00:42:02,718 you can see all the young are of slightly different ages. 389 00:42:02,887 --> 00:42:06,880 That is because they belong to different parents. 390 00:42:08,807 --> 00:42:13,597 Only one pair is on guard. The others are away grazing. 391 00:42:13,767 --> 00:42:16,327 This is a communal creche. 392 00:42:16,487 --> 00:42:20,685 It's based around a hole often dug initially by burrowing owls. 393 00:42:20,847 --> 00:42:24,044 The maras have simply enlarged it. 394 00:42:27,807 --> 00:42:30,799 The adults guard each other's offspring, 395 00:42:30,967 --> 00:42:35,757 but each female will only give her milk to her own babies. 396 00:42:38,687 --> 00:42:44,557 The others must wait until their own mother arrives to take her turn as guard. 397 00:42:47,727 --> 00:42:49,718 Here comes the next pair. 398 00:42:49,887 --> 00:42:53,675 Adults are not always related, so the changing of the guard 399 00:42:53,847 --> 00:42:57,123 can be a somewhat tense business. 400 00:43:10,407 --> 00:43:15,800 The mara couples behave as though they were rivals rather than friends. 401 00:43:34,567 --> 00:43:39,846 Galloping around, grazing, the maras have evolved long legs. 402 00:43:40,007 --> 00:43:42,646 They look more like antelopes. 403 00:43:42,807 --> 00:43:46,197 That may be why they're not good at digging 404 00:43:46,367 --> 00:43:50,360 and prefer to steal holes from the burrowing owls. 405 00:43:52,327 --> 00:43:56,320 A plover warns of approaching danger. 406 00:43:56,487 --> 00:43:59,081 (PLOVER CHIRRUPS) 407 00:44:02,367 --> 00:44:06,599 The babies, thanks to the owls, have a hole to go to. 408 00:44:08,687 --> 00:44:13,044 It's not big enough for the adults. All they can do is run. 409 00:44:27,487 --> 00:44:33,403 There is yet another kind of rodent that gather in vast numbers to graze. 410 00:44:45,847 --> 00:44:49,442 They remind one of the huge herds you see 411 00:44:49,607 --> 00:44:52,405 on the savannahs of East Africa. 412 00:44:53,287 --> 00:44:55,482 But we're in South America, 413 00:44:55,647 --> 00:44:59,435 and these are not wildebeest or antelope. 414 00:44:59,607 --> 00:45:04,203 These are the biggest rodents in the world: capybara. 415 00:45:08,487 --> 00:45:12,275 Capybara are, like mara, related to guinea pigs, 416 00:45:12,447 --> 00:45:18,636 but these are real giants that use their rodent teeth to crop grass, 417 00:45:18,807 --> 00:45:20,843 lots of it. 418 00:45:22,607 --> 00:45:24,598 (SQUEAKING BARK) 419 00:45:26,407 --> 00:45:31,401 When they want to, they can gallop as fast as a small horse. 420 00:45:35,807 --> 00:45:40,801 Although they're very agile on land, they are equally at home in water. 421 00:46:15,527 --> 00:46:20,521 Within these herds, each family sticks together in groups of 20 or so. 422 00:46:20,687 --> 00:46:25,681 There are mothers and daughters, children and grandchildren. 423 00:46:27,687 --> 00:46:32,681 And just one large, dominant male. That's him at the back. 424 00:46:32,847 --> 00:46:37,637 He marks his territory with scent from a gland on the top of his nose. 425 00:46:46,447 --> 00:46:52,044 And he will chase off any rival males that venture too close to his family, 426 00:46:52,207 --> 00:46:54,926 particularly to his females. 427 00:47:19,687 --> 00:47:23,077 Capybara will graze out on the dry savannahs, 428 00:47:23,247 --> 00:47:26,842 but they're most at home in the water. 429 00:47:27,007 --> 00:47:31,205 They have oily, water-resistant fur, partially webbed feet, 430 00:47:31,367 --> 00:47:35,440 and their eyes and nostrils are on the top of their heads. 431 00:47:35,607 --> 00:47:40,237 Almost completely submerged, they can hear, see, and smell 432 00:47:40,407 --> 00:47:43,399 what is happening on dry land nearby. 433 00:47:43,567 --> 00:47:47,958 Even the male's scent gland, which other rodents carry on their cheeks, 434 00:47:48,127 --> 00:47:52,166 has migrated up to the top of his nose. 435 00:47:53,087 --> 00:47:56,284 During the rainy seasons, the plains flood. 436 00:47:56,447 --> 00:47:59,166 The capybara are in their element. 437 00:48:00,207 --> 00:48:04,200 If maras are the South American equivalent of antelope, 438 00:48:04,367 --> 00:48:08,804 these surely are the rodent's version of hippopotamus. 439 00:48:08,967 --> 00:48:13,518 Rodents truly are the most adaptable of mammals.