1 00:00:58,000 --> 00:01:01,010 In the lands between the Arctic Circle and the tropics, 2 00:01:01,170 --> 00:01:04,640 each year brings a great change between winter and summer, 3 00:01:04,800 --> 00:01:09,770 imposing a rhythm in the lives of animals and plants. 4 00:01:10,270 --> 00:01:12,770 Up north in the great evergreen forests, 5 00:01:12,940 --> 00:01:16,150 conditions in mid-winter are cripplingly severe. 6 00:01:24,530 --> 00:01:27,330 Life, if it is to flourish, has three needs: 7 00:01:27,780 --> 00:01:31,120 Light, warmth and moisture. 8 00:01:31,500 --> 00:01:35,830 And the reason trees like these don't grow much farther north 9 00:01:36,000 --> 00:01:38,590 is not only the extreme cold, 10 00:01:38,750 --> 00:01:41,880 but with the long months of winter darkness, 11 00:01:42,090 --> 00:01:45,720 there is not enough light in the year for them to grow. 12 00:01:46,090 --> 00:01:51,720 Here in northern Norway, 300 miles, 500km north of the Arctic Circle, 13 00:01:51,930 --> 00:01:55,940 there is just enough light, but it does get extremely cold. 14 00:01:56,350 --> 00:02:00,570 70 degrees of frost have been measured here, 15 00:02:00,780 --> 00:02:04,490 and in winter there are very heavy snowfalls. 16 00:02:07,410 --> 00:02:10,950 The cold threatens to freeze the liquid within the trees, 17 00:02:11,120 --> 00:02:15,120 and denies them one of their essential supplies: Water. 18 00:02:15,540 --> 00:02:17,960 Although snow and ice lie all around, 19 00:02:18,130 --> 00:02:21,170 the trees can't tap that water while it's frozen. 20 00:02:21,500 --> 00:02:25,550 So this land is effectively as parched as a desert 21 00:02:25,720 --> 00:02:30,350 and the pine trees have as great a need to conserve water as a cactus. 22 00:02:34,980 --> 00:02:38,150 All plants lose some water through their leaves, 23 00:02:38,310 --> 00:02:43,530 but pine needles are protected by a near-impermeable rind. 24 00:02:44,030 --> 00:02:46,240 The pores through which they breathe, 25 00:02:46,450 --> 00:02:49,030 and from which water can evaporate, 26 00:02:49,200 --> 00:02:51,490 are kept out of the wind by being placed 27 00:02:51,660 --> 00:02:55,080 along the groove that runs the length of the needle, 28 00:02:55,290 --> 00:02:58,250 each in a tiny pit ringed with a ridge. 29 00:03:01,630 --> 00:03:05,010 These dry, waxy leaves are almost inedible, 30 00:03:05,170 --> 00:03:08,300 but the seeds in the cones are not, 31 00:03:08,510 --> 00:03:13,310 and are one of the few kinds of food available in the forest in winter. 32 00:03:17,140 --> 00:03:22,520 The crossbill's special beak enables it to separate the cone's segments 33 00:03:22,730 --> 00:03:25,490 and prise out the nutritious seeds. 34 00:03:31,370 --> 00:03:33,660 This winter feast is never certain. 35 00:03:34,490 --> 00:03:37,830 Some years every branch of the trees will be laden with cones, 36 00:03:38,000 --> 00:03:39,960 in others there will only be a handful. 37 00:03:40,120 --> 00:03:43,840 Then the seed-eaters must move on or die. 38 00:03:45,920 --> 00:03:50,050 The few remaining cones can then shed their seeds into the snow 39 00:03:50,260 --> 00:03:53,100 when there are few animals around. 40 00:03:58,180 --> 00:04:00,440 Even so, there are some. 41 00:04:04,190 --> 00:04:09,110 Voles make their runways through the snow and collect what they can. 42 00:04:12,910 --> 00:04:15,870 Moose get little nourishment from pine trees, 43 00:04:16,080 --> 00:04:20,870 apart from the shaggy moss that hangs from the branches. 44 00:04:33,390 --> 00:04:36,430 They chew the sappy twigs and bark of birch, 45 00:04:36,600 --> 00:04:41,390 but there's not enough to keep them going. 46 00:04:41,690 --> 00:04:47,110 If it wasn't for the fat reserves they built up in summer, few would survive. 47 00:04:51,450 --> 00:04:54,530 The winter forests can support very few plant-eaters, 48 00:04:54,700 --> 00:04:59,200 but there are just enough to feed one or two hardy hunters. 49 00:05:19,220 --> 00:05:23,520 The great grey owl's legs are ideal for grabbing prey in snow: 50 00:05:23,690 --> 00:05:26,940 Long and covered with warm feathers. 51 00:05:27,400 --> 00:05:29,070 It regularly patrols the snow, 52 00:05:29,280 --> 00:05:32,400 for it can't afford to miss a single opportunity of a meal. 53 00:05:59,810 --> 00:06:02,810 And this is an incautious move. 54 00:06:39,640 --> 00:06:42,310 Lynx seek bigger prey. 55 00:06:55,650 --> 00:06:58,320 The female has young, which, though large, 56 00:06:58,490 --> 00:07:03,450 are not yet skilled enough to hunt for themselves, so they rely on her. 57 00:07:13,800 --> 00:07:17,180 The cost-efficiency of hunting is precisely calculated. 58 00:07:19,930 --> 00:07:22,850 If the lynx doesn't catch a hare within 200 yards, 59 00:07:23,010 --> 00:07:27,640 the meat it might provide is not enough to warrant the effort, 60 00:07:27,850 --> 00:07:29,440 and the lynx gives up. 61 00:07:35,070 --> 00:07:37,570 Bigger prey are worth much longer chases, 62 00:07:37,740 --> 00:07:41,450 and the lynx pursue roe deer with great persistence. 63 00:07:54,170 --> 00:07:57,920 A single deer will provide food for the whole lynx family. 64 00:08:08,060 --> 00:08:12,150 In this bleak land, even the most ferocious and capable hunters 65 00:08:12,310 --> 00:08:14,360 do not scorn to scavenge. 66 00:08:20,280 --> 00:08:22,660 An eagle owl will take cold deer flesh 67 00:08:22,820 --> 00:08:25,700 just as eagerly as the warm bodies of voles. 68 00:08:29,460 --> 00:08:32,040 A wolverine, the biggest of the weasel family, 69 00:08:32,210 --> 00:08:34,590 and more than a match for an eagle owl. 70 00:09:14,540 --> 00:09:17,590 The coniferous forest grows right round the globe 71 00:09:17,800 --> 00:09:21,800 in a belt that, in places, is 1,200 miles across. 72 00:09:25,180 --> 00:09:28,890 From Scandinavia, it extends across northern Europe and Siberia 73 00:09:29,100 --> 00:09:30,890 to the shores of the Pacific. 74 00:09:34,150 --> 00:09:36,520 During the last ice age, when the seas were lower, 75 00:09:36,690 --> 00:09:38,900 the Bering Strait did not exist, 76 00:09:39,070 --> 00:09:43,030 so the trees continued into North America, 77 00:09:43,570 --> 00:09:46,830 across northern Canada to the Atlantic. 78 00:09:47,080 --> 00:09:52,160 Consequently, all the trees in this vast forest 79 00:09:52,370 --> 00:09:58,090 and its permanent inhabitants in America, Asia and Europe, are much the same. 80 00:10:01,210 --> 00:10:05,510 But when spring comes, visitors journey up from warmer parts 81 00:10:05,680 --> 00:10:10,180 and each forest takes on its own individual character. 82 00:10:13,770 --> 00:10:15,650 In Scandinavia, a hawk owl, 83 00:10:15,810 --> 00:10:19,770 a nomad that has spent the winter farther south, 84 00:10:19,940 --> 00:10:24,700 comes cruising up north again looking for food and a nest site. 85 00:10:30,410 --> 00:10:33,660 Unlike other owls, it's primarily a daytime hunter, 86 00:10:33,830 --> 00:10:38,170 and relies not so much on its acute hearing as its sharp eyesight 87 00:10:38,330 --> 00:10:42,010 as it waits for the melting snow to reveal rodents. 88 00:11:12,330 --> 00:11:15,120 In pine trees, from Norway to Siberia, 89 00:11:15,290 --> 00:11:18,460 the cock capercaillie claims his territory. 90 00:11:18,630 --> 00:11:23,210 This giant grouse is one of the few creatures that eats pine needles. 91 00:11:25,550 --> 00:11:27,220 His hen takes them too. 92 00:11:44,650 --> 00:11:46,320 Now is the time for nesting. 93 00:11:46,570 --> 00:11:49,110 The hawk owl is in search of a hole in a tree, 94 00:11:49,280 --> 00:11:51,620 for it's already found its partner. 95 00:11:54,700 --> 00:11:57,250 But many tree holes are occupied, 96 00:11:57,460 --> 00:12:02,840 for great numbers of owls have travelled up to feed on the voles. 97 00:12:06,970 --> 00:12:09,010 No owl can dig a hole for itself. 98 00:12:09,180 --> 00:12:13,810 They rely mainly on woodpeckers, and none is a more expert carpenter 99 00:12:13,970 --> 00:12:16,520 than the black woodpecker of northern Europe. 100 00:12:17,770 --> 00:12:22,110 Their sharp beak serves as an excellent chisel, 101 00:12:22,270 --> 00:12:27,820 but most prefer to work in dead trees where the wood is softer. 102 00:12:29,900 --> 00:12:31,410 There are ants near this tree too, 103 00:12:31,610 --> 00:12:35,700 which the woodpeckers rely on for food in winter. 104 00:12:49,010 --> 00:12:51,010 Not all owls use nest holes. 105 00:12:51,260 --> 00:12:54,550 The eagle owl nests on the ground, among rocks. 106 00:12:56,260 --> 00:12:58,100 It already has a clutch of three eggs, 107 00:12:58,270 --> 00:13:02,150 for, being a permanent resident of these forests, it paired early. 108 00:13:13,360 --> 00:13:15,780 Plants now have their chance to breed. 109 00:13:15,950 --> 00:13:19,910 The wood anemones are already in flower, as are the pines. 110 00:13:20,160 --> 00:13:22,750 Each tree produces male and female flowers, 111 00:13:22,960 --> 00:13:25,540 which mature at different times, 112 00:13:25,750 --> 00:13:30,170 so the female flowers are likely to be fertilised by pollen from other trees. 113 00:13:33,760 --> 00:13:37,470 Now it is as warm as it ever will be in the northern forests. 114 00:13:37,720 --> 00:13:41,600 Summer visitors are arriving, and the trees echo with their song. 115 00:13:47,980 --> 00:13:51,320 This willow warbler, singing so vigorously in Scandinavia, 116 00:13:51,530 --> 00:13:55,070 has come all the way from the savannah country south of the Sahara. 117 00:13:55,530 --> 00:13:56,830 So has the winchat. 118 00:13:59,790 --> 00:14:01,870 And the lure that has brought them so far 119 00:14:02,040 --> 00:14:05,500 is the sudden emergence of myriads of insects. 120 00:14:16,470 --> 00:14:21,220 This bedraggled creature is hardly recognisable, for its wings have not yet expanded. 121 00:14:21,470 --> 00:14:22,930 It's a pine beauty moth, 122 00:14:23,100 --> 00:14:27,810 and its first priority is to leave the forest floor which is full of danger. 123 00:14:28,310 --> 00:14:30,780 But not all the moths have such a clear run. 124 00:14:37,280 --> 00:14:39,700 Shrews are among the first to feed on them. 125 00:14:42,330 --> 00:14:45,960 Up among the pine needles, the pine beauty pumps fluid out of its body 126 00:14:46,120 --> 00:14:48,500 and into the veins of its wings. 127 00:14:58,220 --> 00:15:02,970 Here the moths will lay their eggs so their caterpillars can feed on the young shoots 128 00:15:04,430 --> 00:15:07,020 The wood ants have missed their chance to catch the adult moth, 129 00:15:07,190 --> 00:15:10,320 but now they're looking for the caterpillars among the branches. 130 00:15:12,980 --> 00:15:16,950 The colour and the pattern of the caterpillar conceals it from birds which hunt by sight, 131 00:15:17,160 --> 00:15:21,490 but is no protection against ants which search by smell and touch. 132 00:15:50,900 --> 00:15:55,070 Finally the body is hauled down to the nest for all to consume. 133 00:16:02,660 --> 00:16:06,450 The caterpillars of the sawfly are also swarming on the pine shoots. 134 00:16:06,660 --> 00:16:10,210 They do have a defence against ants: A chemical one. 135 00:16:10,630 --> 00:16:16,300 As they chew, they store some of the resin from the pine needles in a pouch inside their mouth. 136 00:16:16,710 --> 00:16:22,390 When a foraging ant discovers them, they dab a spot of this resin on its head, like this. 137 00:16:26,930 --> 00:16:33,730 The resin damages the ant's eyes and antennae, so disorientating it that it can hardly walk. 138 00:16:34,650 --> 00:16:36,480 Even if it finds its way back to the nest, 139 00:16:36,650 --> 00:16:42,490 it smells so strongly and strangely that the other ants treat it as an intruder and kill it 140 00:16:49,000 --> 00:16:51,500 The ants themselves are food for others. 141 00:16:54,090 --> 00:16:58,550 The wryneck is a member of the woodpecker family that has specialised in eating ants, 142 00:16:58,720 --> 00:17:01,220 and particularly relishes their cocoons. 143 00:17:06,510 --> 00:17:12,480 Like its cousins, the wryneck nests in holes in trees, but it doesn't excavate them for itself. 144 00:17:12,730 --> 00:17:16,520 It is yet another tenant of vacated woodpecker holes. 145 00:17:27,080 --> 00:17:32,120 With a long tongue you can even collect insects from the bark without leaving your nest. 146 00:17:34,960 --> 00:17:37,920 Here in the far north, close to the Arctic Circle, 147 00:17:38,090 --> 00:17:42,840 the sun during the summer hardly sinks below the horizon and the nights are brief. 148 00:17:49,390 --> 00:17:53,810 The eagle owl hunts just as effectively in the twilight as in the dark. 149 00:17:54,100 --> 00:17:58,360 It has a rabbit. The season is a good one and game is abundant. 150 00:18:01,190 --> 00:18:05,030 Down in the nest on the forest floor, there is only one chick left. 151 00:18:05,240 --> 00:18:07,740 The other two may have been taken by foxes. 152 00:18:12,620 --> 00:18:17,590 Eagle owls often kill rival species, and this chick's last meal was a short-eared owl, 153 00:18:17,790 --> 00:18:19,340 which it's not yet finished. 154 00:18:20,920 --> 00:18:23,680 The single survivor has a superabundance of food. 155 00:18:23,880 --> 00:18:28,720 It has grown fast and its adult feathers are already appearing through its down. 156 00:18:30,680 --> 00:18:33,640 The tail of a red squirrel is left over from a previous meal, 157 00:18:33,810 --> 00:18:35,810 and it even takes that too. 158 00:18:50,540 --> 00:18:53,200 The voles are swarming on the forest floor. 159 00:18:53,450 --> 00:18:56,420 Last winter, the pines produced great quantities of seed, 160 00:18:56,620 --> 00:18:59,380 so many adult voles survived till spring 161 00:18:59,540 --> 00:19:02,920 and now they're all breeding at an extraordinary rate. 162 00:19:03,130 --> 00:19:06,340 This female produced her four young only three weeks ago, 163 00:19:06,510 --> 00:19:11,760 but she is already pregnant again and will soon abandon this family and start a new one. 164 00:19:39,960 --> 00:19:42,920 All the owls, some visitors, some residents, 165 00:19:43,090 --> 00:19:45,470 scour the forest for voles. 166 00:19:55,020 --> 00:20:01,820 Tengmalm's owl, up in a tree hole, has three chicks, all flourishing and all demanding voles. 167 00:20:33,140 --> 00:20:35,180 The number of voles varies considerably. 168 00:20:35,350 --> 00:20:38,940 It gradually builds up over a period of five to six years 169 00:20:39,140 --> 00:20:45,110 until finally there are so many that they eat out their food supply and the population crashes. 170 00:20:45,610 --> 00:20:48,280 These changes have their effect on the owl population. 171 00:20:48,610 --> 00:20:50,990 More voles mean better-fed owls, 172 00:20:51,160 --> 00:20:54,580 which produce bigger clutches of eggs and rear more chicks. 173 00:20:54,830 --> 00:20:59,000 And as the number of owls increases, so they spread out into new territory. 174 00:21:00,870 --> 00:21:04,630 I'm in Finland, very close to the Russian border. 175 00:21:04,880 --> 00:21:09,720 In fact, those pine forests behind me are actually in Russia. 176 00:21:10,010 --> 00:21:14,640 But the frontier is no barrier to the bird they call the phantom of the north, 177 00:21:14,800 --> 00:21:16,310 the great grey owl, 178 00:21:16,470 --> 00:21:19,600 and in years when the vole population is high, 179 00:21:19,770 --> 00:21:26,150 the owl comes across these frontiers and into the Finnish pine forests. 180 00:21:26,400 --> 00:21:29,530 And I know they are here already because I have just picked up this. 181 00:21:29,740 --> 00:21:32,070 This is an owl pellet. 182 00:21:32,410 --> 00:21:39,790 All owls, as part of their natural digestion, throw up the fur and bones of their prey. 183 00:21:40,040 --> 00:21:44,880 And this, I can see, has actually got vole skulls in it. 184 00:21:45,080 --> 00:21:50,420 But to discover exactly what the state of the vole population is at the moment, 185 00:21:50,590 --> 00:21:58,600 I'll have to look inside the nest of a great grey and to do that I'll need this. 186 00:21:59,310 --> 00:22:06,520 All owls are fairly ferocious and the great grey owl certainly can be, 187 00:22:06,690 --> 00:22:11,610 so as part of the standard equipment of looking for owl nests you need this. 188 00:22:16,530 --> 00:22:21,580 Up there is one of their nests, and the female has just flown off. 189 00:22:21,790 --> 00:22:25,790 She's perching in that tree over there, keeping a very close eye on me. 190 00:22:26,000 --> 00:22:28,290 If I go up and have a look in the nest, 191 00:22:28,500 --> 00:22:33,760 I may be able to get some idea as to how the vole cycle is going. 192 00:22:46,440 --> 00:22:51,320 And... come on... 193 00:22:51,480 --> 00:22:53,820 there is just one chick. 194 00:22:54,070 --> 00:22:58,160 If the voles had been at the height of their population, 195 00:22:58,370 --> 00:23:02,700 there would probably be four chicks in such a nest as this, 196 00:23:02,910 --> 00:23:06,040 but the fact there is only one makes it pretty clear 197 00:23:06,250 --> 00:23:10,170 that the vole population is already beginning to crash. 198 00:23:10,670 --> 00:23:19,430 So it is very likely the female and her mate will soon be on their way back to Russia. 199 00:23:23,890 --> 00:23:27,600 There's now just a month left of the short northern summer. 200 00:23:27,900 --> 00:23:31,360 Many of the birds that came up here to harvest the insects and to breed 201 00:23:31,520 --> 00:23:36,030 will soon be moving back again to avoid the severities of the coming winter. 202 00:23:37,410 --> 00:23:41,870 Some, like the redwing, will go to open pastureland down south. 203 00:23:42,450 --> 00:23:45,040 The brambling prefers beech woodland, 204 00:23:45,250 --> 00:23:48,330 and will leave almost as soon as it has finished its summer moult. 205 00:23:55,590 --> 00:23:58,220 The hawk owl is driven south by hunger, 206 00:23:58,510 --> 00:24:03,390 for as the forest gets colder, there is less food to be found. 207 00:24:04,390 --> 00:24:08,480 As it flies south, so the trees beneath change character. 208 00:24:08,770 --> 00:24:14,400 The ranks of dark conifers are replaced by the brighter green of the broadleaved trees: 209 00:24:14,610 --> 00:24:18,150 Oak and ash, birch and beech. 210 00:24:43,970 --> 00:24:50,190 Down here, the weather's warmer, the summers are longer, and the woodlands are free of frost, 211 00:24:50,350 --> 00:24:54,190 not for just two or three months in the year, but for eight or nine, 212 00:24:54,520 --> 00:24:56,940 and the shape of the trees is very different. 213 00:24:57,150 --> 00:25:01,570 Instead of their branches drooping down, and so shedding the snow, 214 00:25:01,780 --> 00:25:04,490 these branches spread out widely, 215 00:25:04,700 --> 00:25:09,620 carrying tier upon tier of leaves with which to catch the abundant energy of the sun. 216 00:25:09,870 --> 00:25:11,710 And the leaves are very different. 217 00:25:11,920 --> 00:25:16,960 They are not covered with a thick, protective rind but are thin, delicate structures. 218 00:25:18,130 --> 00:25:20,510 During the summer water is more accessible, 219 00:25:20,720 --> 00:25:24,140 so there is less need to take rigorous measures to conserve it. 220 00:25:24,510 --> 00:25:29,310 Indeed, during hot days the trees evaporate large quantities to keep cool. 221 00:25:29,560 --> 00:25:31,810 So the pores through which they breathe are numerous, 222 00:25:32,020 --> 00:25:34,900 and not in pits as they are in the pines. 223 00:25:39,030 --> 00:25:46,030 These succulent, soft leaves, unlike pine needles, are relished as food by all kinds of creatures. 224 00:25:52,290 --> 00:25:54,750 Large animals, like deer, take many of them, 225 00:25:54,960 --> 00:25:59,840 but the greatest quantity by far is gathered by insects. 226 00:26:26,370 --> 00:26:31,830 The forest canopy in late summer has more birds in it than at any other time of the year. 227 00:26:32,080 --> 00:26:34,920 There are returning migrants newly arrived from the north, 228 00:26:35,080 --> 00:26:39,210 resident breeders gathering food to feed their second families of the season, 229 00:26:39,380 --> 00:26:42,510 and young fledglings starting to forage for themselves 230 00:26:42,670 --> 00:26:46,010 and still not sure what is edible and what isn't. 231 00:26:46,390 --> 00:26:51,520 Nearly all of them are hunting for insects, and the crop they take is huge. 232 00:27:04,820 --> 00:27:09,370 Not surprisingly, the insects have evolved many ways of protecting themselves. 233 00:27:09,580 --> 00:27:13,870 They snip off half-eaten leaves so as to give the minimum sign of their presence. 234 00:27:14,080 --> 00:27:17,920 They disguise themselves as a blob of cuckoo spit or a bird dropping, 235 00:27:18,080 --> 00:27:22,550 but if they move, as eventually they must, their concealment is lost. 236 00:27:34,060 --> 00:27:37,100 Some hang in places which are difficult to reach. 237 00:27:37,400 --> 00:27:43,940 This might baffle a fledgling, but an adult great tit is both experienced and agile. 238 00:27:53,830 --> 00:27:57,420 The tree creeper specialises in insects that live on bark. 239 00:28:01,500 --> 00:28:05,880 A poplar hawk moth tries to defend itself by pretending to be fierce. 240 00:28:20,360 --> 00:28:23,690 The nuthatch habitually works its way down the trunk, 241 00:28:23,900 --> 00:28:26,570 and that way may see insects that have been overlooked 242 00:28:26,740 --> 00:28:29,570 by tree creepers that habitually come up it. 243 00:28:48,470 --> 00:28:50,720 One of the most expert of all bark-feeders, 244 00:28:50,930 --> 00:28:55,850 and in some ways the most specialised of all the birds living in the tall trees of these forest 245 00:28:56,020 --> 00:28:57,640 are the woodpeckers. 246 00:28:58,230 --> 00:29:00,770 The greater spotted woodpecker is typical of them. 247 00:29:00,940 --> 00:29:03,900 Its hearing is excellent and it locates the grubs it seeks 248 00:29:04,070 --> 00:29:08,190 by the tiny sounds they make as they move inside the bark. 249 00:29:11,700 --> 00:29:16,370 Its tall feathers have strong quills and serve as props for its body. 250 00:29:17,410 --> 00:29:22,790 Its bill has a resilient pad at the base which cushions its brain from the shock of its drilling. 251 00:29:25,590 --> 00:29:31,720 Its feet give it a grip in all directions, with two toes pointing forwards and two backwards. 252 00:29:32,590 --> 00:29:35,430 Each continent has its own range of woodpeckers. 253 00:29:35,680 --> 00:29:37,100 Europe has ten species, 254 00:29:37,270 --> 00:29:41,020 but here in North America there are over twice as many. 255 00:29:41,390 --> 00:29:46,650 This one, a sapsucker, drills holes in trees not for insects, but for sap. 256 00:29:47,070 --> 00:29:50,530 It digs lines of these wells in many kinds of trees. 257 00:29:51,110 --> 00:29:55,330 Each little hole points slightly downwards so that the sap does not trickle out 258 00:29:55,530 --> 00:29:57,950 but collects in a small pool inside, 259 00:29:58,160 --> 00:30:00,540 and the sapsucker collects it with its tongue. 260 00:30:01,250 --> 00:30:02,540 And so do other birds. 261 00:30:07,630 --> 00:30:08,710 A hummingbird. 262 00:30:08,880 --> 00:30:11,970 Most of its family live in the tropics and feed on nectar, 263 00:30:12,220 --> 00:30:17,560 but this one comes north in the summer and finds tree sap just as acceptable. 264 00:30:19,310 --> 00:30:22,020 Flies, too, come to the sweet sap. 265 00:30:39,160 --> 00:30:43,410 In late summer, the parent sapsuckers lead their fledglings to the wells 266 00:30:43,620 --> 00:30:48,550 and leave them to feast not only on the sap but on the insects it attracts 267 00:30:51,420 --> 00:30:57,760 This American woodpecker uses its drilling skills to bore neat sockets in dead tree trunks. 268 00:30:58,470 --> 00:31:01,350 Acorns are its main food, but during the season, 269 00:31:01,520 --> 00:31:04,770 there are far more acorns than the woodpeckers can eat immediately. 270 00:31:05,230 --> 00:31:06,860 But they don't leave them for others. 271 00:31:07,190 --> 00:31:11,650 Several birds share a communal acorn treasury, like this one. 272 00:31:11,940 --> 00:31:16,740 They hammer the acorns into the holes so firmly that few other creatures can get them out, 273 00:31:16,910 --> 00:31:21,950 and the store will keep the acorn woodpeckers supplied throughout the year. 274 00:31:28,330 --> 00:31:32,800 The ripening acorns herald the end of summer and the beginning of autumn. 275 00:31:33,130 --> 00:31:36,590 Trees and bushes proffer their seeds to the forest animals. 276 00:31:36,840 --> 00:31:39,430 Some are wrapped in soft and tasty flesh 277 00:31:39,640 --> 00:31:43,810 to tempt the animals to eat them and so transport them to new sites. 278 00:31:45,770 --> 00:31:47,350 Others are packed with nourishment, 279 00:31:47,520 --> 00:31:51,230 not for animals, but to provide food for the germinating seedling, 280 00:31:51,400 --> 00:31:53,530 but the animals eat them just the same. 281 00:31:54,110 --> 00:32:00,490 Even the hard and unpromising looking acorns of the American pin oak are collected by racoons. 282 00:32:10,630 --> 00:32:16,550 The squirrel's habit of burying acorns for a winter store has been the begining of many an oak. 283 00:32:19,090 --> 00:32:24,140 The black bear, on occasion, will eat fish and voles and even carrion, 284 00:32:24,350 --> 00:32:26,560 but much of its diet is vegetable. 285 00:32:27,060 --> 00:32:29,310 It will dig for roots and even eat pine cones, 286 00:32:29,480 --> 00:32:34,070 but it has a very sweet tooth and just now it relishes the fruit. 287 00:32:49,420 --> 00:32:53,250 All sorts of mammals are now clambering around in the trees in search of fruit. 288 00:32:53,460 --> 00:32:56,420 The possum, a strange primitive animal of the Americas 289 00:32:56,630 --> 00:33:01,010 related more closely to kangaroos than to rats, eats almost anything. 290 00:33:05,810 --> 00:33:09,810 Few of them can get to the very tops of the trees or the thinnest twig, 291 00:33:09,980 --> 00:33:11,810 but a chipmunk can. 292 00:33:15,860 --> 00:33:18,860 The chills of autumn presage the coming of winter. 293 00:33:19,530 --> 00:33:23,120 The delicate leaves worked efficiently throughout the warm moist summer, 294 00:33:23,280 --> 00:33:25,330 but they are not suited to cold weather. 295 00:33:25,830 --> 00:33:27,250 Frost will damage them. 296 00:33:27,700 --> 00:33:30,000 Their abundant pores would lose too much water. 297 00:33:30,250 --> 00:33:34,540 So the green chlorophyll in them is broken down and withdrawn into the tree, 298 00:33:34,710 --> 00:33:37,840 revealing the red and brown waste products, 299 00:33:38,130 --> 00:33:40,050 and the leaves fall. 300 00:33:41,550 --> 00:33:44,930 And they, too, provide food for another woodland community, 301 00:33:45,100 --> 00:33:47,600 the inhabitants of the leaf litter. 302 00:33:51,190 --> 00:33:55,770 There may be 100,000 box mites in every cubic yard. 303 00:33:56,860 --> 00:33:58,490 And there are many other creatures too, 304 00:33:58,690 --> 00:34:00,820 chewing their way through the dead leaves, 305 00:34:01,030 --> 00:34:03,200 extracting what nutriment they can 306 00:34:03,360 --> 00:34:07,490 and leaving the remainder to be dealt with by fungi and bacteria. 307 00:34:15,340 --> 00:34:18,000 They themselves are hunted by monsters in miniature, 308 00:34:18,170 --> 00:34:19,710 pseudoscorpions, 309 00:34:20,010 --> 00:34:25,300 horrific in close-up, but, perhaps fortunately, the size of a pinhead. 310 00:35:03,010 --> 00:35:08,300 Snails are giants in comparison and, since they carry their shells around with them, 311 00:35:08,470 --> 00:35:13,350 they might seem to be fairly well protected against any creatures smaller than a bird. 312 00:35:13,850 --> 00:35:18,310 But one particular beetle has specialised equipment for dealing with them. 313 00:35:20,570 --> 00:35:23,570 Its head and jaws are long and thin. 314 00:35:52,390 --> 00:35:54,980 Almost hidden in the leaves of these American woods 315 00:35:55,190 --> 00:35:59,860 are some spectacularly coloured little creatures hardly bigger than worms. 316 00:36:04,030 --> 00:36:06,570 They are amphibians: Salamanders. 317 00:36:06,910 --> 00:36:12,240 Almost every mountain range in the US has its own species with its own colours, 318 00:36:12,410 --> 00:36:15,000 but, being nocturnal, they're rarely seen. 319 00:36:37,230 --> 00:36:42,110 Shrews eat most small living things they come across, and they are formidable hunters, 320 00:36:42,270 --> 00:36:45,190 for they are one of the few mammals that has a poisonous bite. 321 00:36:52,080 --> 00:36:57,160 The salamander's only defence is to produce an acrid liquid from glands on its tail 322 00:36:57,620 --> 00:37:02,460 The first time a shrew encounters this, it usually takes no notice and eats the salamander, 323 00:37:02,630 --> 00:37:04,800 but apparently the taste is not very nice, 324 00:37:04,960 --> 00:37:07,340 for on later encounters, like this one, 325 00:37:07,510 --> 00:37:10,890 one sniff reminds the shrew the meal won't be a good one 326 00:37:11,090 --> 00:37:13,680 and it leaves the salamander alone. 327 00:37:20,600 --> 00:37:23,060 The summer visitors have departed. 328 00:37:23,730 --> 00:37:25,280 The woods have fallen silent. 329 00:37:25,530 --> 00:37:29,320 The days are shortening and the temperature falling. 330 00:38:01,600 --> 00:38:06,070 Eventually the land is gripped tight by frost. 331 00:38:33,380 --> 00:38:34,470 It's late winter. 332 00:38:34,680 --> 00:38:37,890 The once-resplendent trees are now mere skeletons 333 00:38:38,060 --> 00:38:42,730 and life in these woodlands has come almost to a standstill. 334 00:38:42,940 --> 00:38:45,860 The trees, without their leaves, can't grow. 335 00:38:46,110 --> 00:38:50,940 The birds that came visiting up here during the summer have now retreated south, 336 00:38:51,190 --> 00:38:56,490 and some of these small mammals have crawled into holes and gone to sleep. 337 00:38:56,740 --> 00:39:02,080 Their heartbeat has almost stopped, their bodies have become as cold as stone. 338 00:39:02,330 --> 00:39:03,670 They're hibernating. 339 00:39:03,920 --> 00:39:07,920 But that sleep doesn't last throughout the winter. 340 00:39:08,090 --> 00:39:11,800 They wake up every four or five days and go and look for food. 341 00:39:12,050 --> 00:39:15,220 Like, for example, those small chipmunks over there. 342 00:39:16,300 --> 00:39:19,310 Not only warmth but intense cold will bring them out, 343 00:39:19,510 --> 00:39:22,600 for although their body temperature falls while they hibernate, 344 00:39:22,770 --> 00:39:25,560 if it drops to freezing point, they will die. 345 00:39:25,810 --> 00:39:30,360 So in really cold spells, they must get up and warm themselves with a little exercise, 346 00:39:30,530 --> 00:39:33,780 even though it dangerously depletes their fat reserves. 347 00:39:35,530 --> 00:39:39,200 But in these American woodlands there is one spectacular sleeper 348 00:39:39,370 --> 00:39:41,450 who dozes for months on end. 349 00:39:43,410 --> 00:39:44,580 Just look at this. 350 00:39:52,340 --> 00:39:53,880 A black bear. 351 00:39:56,430 --> 00:40:00,430 She retired to this den in early autumn, and after a month or so of drowsiness, 352 00:40:00,600 --> 00:40:01,850 produced her cubs. 353 00:40:02,100 --> 00:40:06,730 In the colder northern parts of these woods, she may spend six or seven months here, 354 00:40:06,940 --> 00:40:08,900 during which time she suckles her cubs 355 00:40:09,060 --> 00:40:13,030 but neither feeds herself nor urinates nor defecates. 356 00:40:13,320 --> 00:40:16,650 So she spends the majority of her life half-asleep. 357 00:40:19,820 --> 00:40:25,540 When spring at last comes, the brown carpet of rotting leaves is suddenly flooded with colour. 358 00:40:28,960 --> 00:40:33,000 The plants that live close to the ground now make haste to sprout and flower 359 00:40:33,170 --> 00:40:34,840 and soak up the spring sunshine 360 00:40:35,050 --> 00:40:39,260 before the trees above produce their own leaves and cut out the light. 361 00:40:43,890 --> 00:40:45,430 The bear's den is empty, 362 00:40:45,600 --> 00:40:48,310 but the owners haven't gone far. 363 00:40:58,400 --> 00:41:01,240 There's still not much to eat, only a few leaves, 364 00:41:01,410 --> 00:41:04,700 nor will there be until the first of the berries come into fruit in summer, 365 00:41:04,870 --> 00:41:07,750 but meanwhile at least the sun is warm. 366 00:41:14,880 --> 00:41:17,420 Another mother spends the spring up in a tree: 367 00:41:17,590 --> 00:41:20,590 A wood duck, only she is about to leave. 368 00:41:27,930 --> 00:41:29,980 The hole has provided a secure nest, 369 00:41:30,150 --> 00:41:33,820 but all ducklings follow their mothers as soon as they hatch. 370 00:42:07,310 --> 00:42:11,980 And now new forms appear from among the dead leaves. 371 00:42:48,850 --> 00:42:50,850 The spring showers soak the woodlands 372 00:42:51,020 --> 00:42:55,230 and create just the moist, warm conditions needed by the fungi 373 00:42:55,400 --> 00:42:57,650 to produce their fruiting bodies. 374 00:42:58,150 --> 00:43:01,820 These must be mature and ready to discharge their microscopic spores 375 00:43:01,990 --> 00:43:05,200 by the time the dry winds of summer begin to blow, 376 00:43:05,410 --> 00:43:09,830 so that their spores, like dust, will be carried all through the forest. 377 00:43:12,660 --> 00:43:16,670 Once, the woods of North America stretched over the eastern half of the continent 378 00:43:16,840 --> 00:43:20,880 in an almost continuous band hundreds of miles deep. 379 00:43:21,510 --> 00:43:25,890 Today, the majority has been felled to make space for farmland and cities, 380 00:43:26,050 --> 00:43:29,350 but enough remains to make plain their splendour. 381 00:43:32,770 --> 00:43:35,310 And now we've come farther south still. 382 00:43:35,520 --> 00:43:40,110 I'm on the borders of Florida and Georgia in the southern United States, 383 00:43:40,320 --> 00:43:44,450 and here it's very hot in the summer and the winters are very mild, 384 00:43:44,650 --> 00:43:47,530 with only a few frosts, and none of them severe. 385 00:43:47,780 --> 00:43:54,620 So some of the broadleaved trees here, like this oak, don't shed all their leaves in the autumn 386 00:43:54,790 --> 00:43:58,840 but keep them throughout the year and continue growing. 387 00:43:59,420 --> 00:44:02,800 And these aren't the only evergreens that are here, either. 388 00:44:03,050 --> 00:44:04,760 There are pines. 389 00:44:05,090 --> 00:44:09,850 In some parts where the soil is very rocky or sandy and poor in nutrients, 390 00:44:10,010 --> 00:44:13,600 the pines will grow because nothing else can survive there. 391 00:44:13,890 --> 00:44:18,980 But this pine forest owes its existence to another factor altogether. 392 00:44:30,160 --> 00:44:33,700 Oak saplings are killed within minutes by fire. 393 00:44:36,330 --> 00:44:41,000 But the terminal buds of young pines are surrounded by a shock of needles. 394 00:44:41,340 --> 00:44:46,550 They burn at a relatively low temperature, and by the time the flames have consumed them, 395 00:44:46,760 --> 00:44:48,680 the main fire has swept by 396 00:44:48,890 --> 00:44:54,560 and the bud at the top of the stem, from which new growth will come, is still unharmed. 397 00:44:57,140 --> 00:45:02,770 Fires like these are not just the work of careless people, they occur naturally. 398 00:45:03,360 --> 00:45:07,530 The spark that regularly sets fire to these forest is lightning. 399 00:45:07,780 --> 00:45:11,240 In this part of the southern States, violent thunderstorms are common 400 00:45:11,410 --> 00:45:13,990 and lightning often strikes the taller trees, 401 00:45:14,160 --> 00:45:19,080 scoring a deep groove down the length of the trunk as it flashes down to earth. 402 00:45:22,210 --> 00:45:26,840 And this at my feet is the tinder which set it aflame. 403 00:45:27,090 --> 00:45:32,720 These are pine needles, and they're so full of resin and they're so dry 404 00:45:32,890 --> 00:45:35,140 that they flame up very easily. 405 00:45:35,310 --> 00:45:39,640 But the fire they produce is not very hot, and it's also very short-lived, 406 00:45:39,810 --> 00:45:44,270 so that if any creature can survive fire for just one or two minutes, 407 00:45:44,480 --> 00:45:47,820 then it can survive a fire like this. 408 00:45:50,780 --> 00:45:53,740 The rattlesnake, like many other ground-living animals, 409 00:45:53,950 --> 00:45:57,290 regularly takes refuge from the midday sun in holes, 410 00:45:57,500 --> 00:46:01,420 so now it knows exactly where to go to escape the fire. 411 00:46:19,060 --> 00:46:23,100 But this hole is already occupied by its digger and owner, 412 00:46:26,940 --> 00:46:28,690 a gopher tortoise. 413 00:46:44,000 --> 00:46:48,670 Rattlesnake and tortoise do not normally interfere with one another... 414 00:47:02,190 --> 00:47:05,440 ...and that seems to be the way things are going to stay. 415 00:47:08,020 --> 00:47:12,200 But in the back of the burrow lies another refugee, an indigo snake, 416 00:47:12,400 --> 00:47:15,700 and it, on occasion, eats rattlesnakes. 417 00:47:38,010 --> 00:47:42,770 But the fire is passing and the rattlesnake can return to the forest. 418 00:47:49,320 --> 00:47:52,860 Some insects don't avoid fire, they actively seek it. 419 00:47:53,070 --> 00:47:55,780 Beetles find it difficult to lay their eggs in the pines 420 00:47:55,950 --> 00:47:58,280 because the trees swamp them with resin. 421 00:47:58,490 --> 00:48:01,740 But a tree killed by fire can't resist, 422 00:48:01,950 --> 00:48:04,750 and these beetles take advantage of the situation. 423 00:48:05,080 --> 00:48:08,960 They have pits behind their legs which are sensitive to infra-red rays, 424 00:48:09,130 --> 00:48:12,090 and therefore they can detect the slightest rise in temperature, 425 00:48:12,260 --> 00:48:16,970 and with these to guide them, they travel from all over the forest to the wake of the fire 426 00:48:17,180 --> 00:48:19,140 and arrive in hundreds. 427 00:48:24,230 --> 00:48:25,810 Quickly they mate. 428 00:48:32,320 --> 00:48:34,820 The females crawl all over the scorched trunks, 429 00:48:34,990 --> 00:48:38,200 seeking crevices in the bark into which they can lay their eggs, 430 00:48:38,410 --> 00:48:43,160 so ensuring that their grubs will have some nice nutritious bark to chew. 431 00:48:45,830 --> 00:48:47,870 As insects assemble in the burnt forest, 432 00:48:48,040 --> 00:48:50,040 the insect-eaters follow. 433 00:48:50,630 --> 00:48:54,760 The oak toad almost exactly matches the colour of the charred forest floor. 434 00:48:57,590 --> 00:49:01,720 Other more conspicuous hunters wait on newly emerged shoots. 435 00:49:08,060 --> 00:49:11,690 Within a couple of months of a summer fire, the forest has more than recovered, 436 00:49:11,860 --> 00:49:13,650 it is rejuvenated. 437 00:49:13,820 --> 00:49:16,400 The fire has cleared away the old growth on the ground, 438 00:49:16,570 --> 00:49:21,660 and by reducing the pine needles to ash has released their nutrients into the soil, 439 00:49:21,870 --> 00:49:26,160 and now the ground sprouts more flowers than at any other time. 440 00:49:39,930 --> 00:49:44,640 Because of regular fires, big bushes can't establish themselves here, 441 00:49:44,890 --> 00:49:50,150 so swampy areas are not colonised and sucked dry by them as happens elsewhere, 442 00:49:50,400 --> 00:49:53,440 and open marshes remain where pitcher plants can grow 443 00:49:53,610 --> 00:49:56,440 and where frogs can swim and breed. 444 00:49:56,690 --> 00:50:03,410 Indeed, one species of frog lives nowhere else but in these pools in the American pine barrens. 445 00:50:20,510 --> 00:50:25,510 The woodpeckers here can't excavate their nest in dead trees as do woodpeckers elsewhere, 446 00:50:25,680 --> 00:50:29,560 for in this fire-ravaged forest they would risk incineration, 447 00:50:29,730 --> 00:50:34,480 so the red-cockaded woodpecker drills its holes in living pines. 448 00:50:34,900 --> 00:50:40,320 But the wood is so hard, it takes several woodpeckers about two years to dig the hole. 449 00:50:43,070 --> 00:50:48,290 Resinous sap seeps out around the hole where the outer layers of the tree have been breached. 450 00:50:48,540 --> 00:50:51,410 So the birds make their hole low down on the trunk 451 00:50:51,620 --> 00:50:56,630 where the inner sap-free heartwood is thick enough to accommodate the entire nest. 452 00:50:57,750 --> 00:51:00,130 The flow of resin is diverted to the outside 453 00:51:00,300 --> 00:51:04,430 by drilling pits like sap wells above and below the hole. 454 00:51:11,430 --> 00:51:17,320 It's in these laboriously excavated holes that the red-cockaded woodpecker raises its young. 455 00:51:25,370 --> 00:51:30,540 The holes are very conspicuous, for each is surrounded by a sheet of yellow congealed resin. 456 00:51:34,210 --> 00:51:39,000 The rat snake is a great robber of nests and stealer of chicks. 457 00:51:53,770 --> 00:51:56,690 It's an extremely skilful tree climber. 458 00:51:57,020 --> 00:52:01,480 Since the woodpecker's hole in the living tree has to be fairly low down on the trunk, 459 00:52:01,860 --> 00:52:07,780 it is within easy reach of the snake and therefore might seem to be in considerable danger. 460 00:52:08,450 --> 00:52:11,080 But now the other function of all that resin, 461 00:52:11,240 --> 00:52:14,120 deliberately produced around the nest by the woodpecker, 462 00:52:14,330 --> 00:52:16,120 is about to become clear. 463 00:52:46,740 --> 00:52:50,490 The chemicals in the resin seem to irritate the snake beyond endurance, 464 00:52:50,660 --> 00:52:52,870 and it arches its body away. 465 00:52:56,290 --> 00:52:58,290 Eventually it's too much. 466 00:53:02,300 --> 00:53:07,380 So fire, one way or another, influences the whole community of animals and plants 467 00:53:07,590 --> 00:53:09,800 in the pine forests of the south. 468 00:53:11,550 --> 00:53:18,060 This injury was also caused by fire, and this is also a coniferous tree, 469 00:53:18,310 --> 00:53:20,150 but a very different one. 470 00:53:20,440 --> 00:53:30,740 To start with, it's over 40 feet across along its base and it's 267-1/2 feet high. 471 00:53:31,120 --> 00:53:34,120 This is a giant sequoia. 472 00:53:35,750 --> 00:53:40,210 It's thought to be about 2,500 years old, 473 00:53:40,420 --> 00:53:47,090 but the largest individual tree of all is this one known as the General Sherman. 474 00:53:47,470 --> 00:53:54,260 It's just taller and it's estimated to weigh 1,385 tons, 475 00:53:54,510 --> 00:53:58,810 which makes it the most massive living organism in the world. 476 00:54:00,770 --> 00:54:05,070 Although these trees are growing almost as far south as the southern pines, 477 00:54:05,230 --> 00:54:09,360 the climate here, 2,000 metres up in the Sierra Nevada mountains, 478 00:54:09,530 --> 00:54:14,240 is much colder and snow lies on the ground for almost half the year. 479 00:54:14,660 --> 00:54:16,540 It's as though, by climbing to this height, 480 00:54:16,700 --> 00:54:20,540 we have returned climatically to the great forests of the north. 481 00:54:20,790 --> 00:54:24,960 During the Ice Age, these sequoias grew over much of North America. 482 00:54:25,250 --> 00:54:28,970 But when, some 8,000 years ago, the earth began to warm, 483 00:54:29,130 --> 00:54:34,430 they died out except for these isolated groups high up in the mountains. 484 00:54:42,730 --> 00:54:46,320 We've travelled some 2,000 miles southwards 485 00:54:46,480 --> 00:54:50,780 since we started at the tree line near the Arctic Circle, 486 00:54:51,110 --> 00:54:57,200 and in all that vast territory the majority of the forest trees have been conifers, 487 00:54:57,490 --> 00:55:04,080 so it seems only right and proper that we should end with these, the noblest of them all. 488 00:55:04,380 --> 00:55:07,630 As a group, the conifers owe much of their success 489 00:55:07,840 --> 00:55:12,180 to their ability to cope with the changeable northern climate. 490 00:55:12,430 --> 00:55:17,140 They can survive both the short, dark days of winter with their bitter cold, 491 00:55:17,310 --> 00:55:21,890 as well as the long sunny days of summer with their raging fires.