1 00:00:54,988 --> 00:00:57,889 In the lands between the Arctic Circle and the tropics, 2 00:00:58,058 --> 00:01:01,357 each year brings a great change between winter and summer, 3 00:01:01,528 --> 00:01:06,295 imposing a rhythm in the lives of animals and plants. 4 00:01:06,766 --> 00:01:09,166 Up north in the great evergreen forests, 5 00:01:09,335 --> 00:01:12,395 conditions in mid-winter are cripplingly severe. 6 00:01:20,447 --> 00:01:23,109 Life, if it is to flourish, has three needs: 7 00:01:23,550 --> 00:01:26,747 Light, warmth and moisture. 8 00:01:27,120 --> 00:01:31,284 And the reason trees like these don't grow much farther north 9 00:01:31,458 --> 00:01:33,926 is not only the extreme cold, 10 00:01:34,094 --> 00:01:37,086 but with the long months of winter darkness, 11 00:01:37,263 --> 00:01:40,755 there is not enough light in the year for them to grow. 12 00:01:41,101 --> 00:01:46,539 Here in northern Norway, 300 miles, 500km north of the Arctic Circle, 13 00:01:46,706 --> 00:01:50,574 there is just enough light, but it does get extremely cold. 14 00:01:50,944 --> 00:01:55,005 70 degrees of frost have been measured here, 15 00:01:55,181 --> 00:01:58,742 and in winter there are very heavy snowfalls. 16 00:02:01,554 --> 00:02:04,955 The cold threatens to freeze the liquid within the trees, 17 00:02:05,125 --> 00:02:08,959 and denies them one of their essential supplies: Water. 18 00:02:09,362 --> 00:02:11,660 Although snow and ice lie all around, 19 00:02:11,831 --> 00:02:14,766 the trees can't tap that water while it's frozen. 20 00:02:15,068 --> 00:02:18,970 So this land is effectively as parched as a desert 21 00:02:19,139 --> 00:02:23,576 and the pine trees have as great a need to conserve water as a cactus. 22 00:02:28,014 --> 00:02:31,040 All plants lose some water through their leaves, 23 00:02:31,217 --> 00:02:36,211 but pine needles are protected by a near-impermeable rind. 24 00:02:36,689 --> 00:02:38,816 The pores through which they breathe, 25 00:02:38,992 --> 00:02:41,460 and from which water can evaporate, 26 00:02:41,628 --> 00:02:43,823 are kept out of the wind by being placed 27 00:02:43,997 --> 00:02:47,296 along the groove that runs the length of the needle, 28 00:02:47,467 --> 00:02:50,300 each in a tiny pit ringed with a ridge. 29 00:02:53,573 --> 00:02:56,804 These dry, waxy leaves are almost inedible, 30 00:02:56,976 --> 00:02:59,968 but the seeds in the cones are not, 31 00:03:00,180 --> 00:03:04,742 and are one of the few kinds of food available in the forest in winter. 32 00:03:08,421 --> 00:03:13,620 The crossbill's special beak enables it to separate the cone's segments 33 00:03:13,793 --> 00:03:16,421 and prise out the nutritious seeds. 34 00:03:22,068 --> 00:03:24,263 This winter feast is never certain. 35 00:03:25,071 --> 00:03:28,268 Some years every branch of the trees will be laden with cones, 36 00:03:28,441 --> 00:03:30,306 in others there will only be a handful. 37 00:03:30,476 --> 00:03:34,037 Then the seed-eaters must move on or die. 38 00:03:36,049 --> 00:03:40,008 The few remaining cones can then shed their seeds into the snow 39 00:03:40,186 --> 00:03:42,916 when there are few animals around. 40 00:03:47,794 --> 00:03:49,955 Even so, there are some. 41 00:03:53,566 --> 00:03:58,265 Voles make their runways through the snow and collect what they can. 42 00:04:01,908 --> 00:04:04,775 Moose get little nourishment from pine trees, 43 00:04:04,944 --> 00:04:09,574 apart from the shaggy moss that hangs from the branches. 44 00:04:21,561 --> 00:04:24,462 They chew the sappy twigs and bark of birch, 45 00:04:24,631 --> 00:04:29,227 but there's not enough to keep them going. 46 00:04:29,502 --> 00:04:34,701 If it wasn't for the fat reserves they built up in summer, few would survive. 47 00:04:38,878 --> 00:04:41,847 The winter forests can support very few plant-eaters, 48 00:04:42,015 --> 00:04:46,315 but there are just enough to feed one or two hardy hunters. 49 00:05:05,538 --> 00:05:09,634 The great grey owl's legs are ideal for grabbing prey in snow: 50 00:05:09,809 --> 00:05:12,937 Long and covered with warm feathers. 51 00:05:13,346 --> 00:05:14,973 It regularly patrols the snow, 52 00:05:15,148 --> 00:05:18,174 for it can't afford to miss a single opportunity of a meal. 53 00:05:44,444 --> 00:05:47,311 And this is an incautious move. 54 00:06:22,648 --> 00:06:25,208 Lynx seek bigger prey. 55 00:06:37,997 --> 00:06:40,557 The female has young, which, though large, 56 00:06:40,733 --> 00:06:45,466 are not yet skilled enough to hunt for themselves, so they rely on her. 57 00:06:55,381 --> 00:06:58,646 The cost-efficiency of hunting is precisely calculated. 58 00:07:01,287 --> 00:07:04,085 If the lynx doesn't catch a hare within 200 yards, 59 00:07:04,257 --> 00:07:08,694 the meat it might provide is not enough to warrant the effort, 60 00:07:08,861 --> 00:07:10,419 and the lynx gives up. 61 00:07:15,802 --> 00:07:18,202 Bigger prey are worth much longer chases, 62 00:07:18,371 --> 00:07:21,932 and the lynx pursue roe deer with great persistence. 63 00:07:34,120 --> 00:07:37,715 A single deer will provide food for the whole lynx family. 64 00:07:47,433 --> 00:07:51,369 In this bleak land, even the most ferocious and capable hunters 65 00:07:51,537 --> 00:07:53,471 do not scorn to scavenge. 66 00:07:59,145 --> 00:08:01,443 An eagle owl will take cold deer flesh 67 00:08:01,614 --> 00:08:04,378 just as eagerly as the warm bodies of voles. 68 00:08:07,954 --> 00:08:10,422 A wolverine, the biggest of the weasel family, 69 00:08:10,590 --> 00:08:12,888 and more than a match for an eagle owl. 70 00:08:51,197 --> 00:08:54,132 The coniferous forest grows right round the globe 71 00:08:54,300 --> 00:08:58,168 in a belt that, in places, is 1,200 miles across. 72 00:09:01,407 --> 00:09:04,968 From Scandinavia, it extends across northern Europe and Siberia 73 00:09:05,144 --> 00:09:06,873 to the shores of the Pacific. 74 00:09:10,016 --> 00:09:12,280 During the last ice age, when the seas were lower, 75 00:09:12,451 --> 00:09:14,544 the Bering Strait did not exist, 76 00:09:14,720 --> 00:09:18,520 so the trees continued into North America, 77 00:09:19,058 --> 00:09:22,152 across northern Canada to the Atlantic. 78 00:09:22,395 --> 00:09:27,298 Consequently, all the trees in this vast forest 79 00:09:27,466 --> 00:09:32,961 and its permanent inhabitants in America, Asia and Europe, are much the same. 80 00:09:35,942 --> 00:09:40,072 But when spring comes, visitors journey up from warmer parts 81 00:09:40,246 --> 00:09:44,546 and each forest takes on its own individual character. 82 00:09:47,987 --> 00:09:49,784 In Scandinavia, a hawk owl, 83 00:09:49,956 --> 00:09:53,756 a nomad that has spent the winter farther south, 84 00:09:53,926 --> 00:09:58,488 comes cruising up north again looking for food and a nest site. 85 00:10:03,970 --> 00:10:07,064 Unlike other owls, it's primarily a daytime hunter, 86 00:10:07,239 --> 00:10:11,403 and relies not so much on its acute hearing as its sharp eyesight 87 00:10:11,577 --> 00:10:15,069 as it waits for the melting snow to reveal rodents. 88 00:10:44,143 --> 00:10:46,839 In pine trees, from Norway to Siberia, 89 00:10:47,013 --> 00:10:50,039 the cock capercaillie claims his territory. 90 00:10:50,216 --> 00:10:54,585 This giant grouse is one of the few creatures that eats pine needles. 91 00:10:56,822 --> 00:10:58,449 His hen takes them too. 92 00:11:15,141 --> 00:11:16,768 Now is the time for nesting. 93 00:11:17,009 --> 00:11:19,443 The hawk owl is in search of a hole in a tree, 94 00:11:19,612 --> 00:11:21,842 for it's already found its partner. 95 00:11:24,784 --> 00:11:27,252 But many tree holes are occupied, 96 00:11:27,420 --> 00:11:32,619 for great numbers of owls have travelled up to feed on the voles. 97 00:11:36,562 --> 00:11:38,530 No owl can dig a hole for itself. 98 00:11:38,698 --> 00:11:43,101 They rely mainly on woodpeckers, and none is a more expert carpenter 99 00:11:43,269 --> 00:11:45,703 than the black woodpecker of northern Europe. 100 00:11:46,939 --> 00:11:51,069 Their sharp beak serves as an excellent chisel, 101 00:11:51,243 --> 00:11:56,545 but most prefer to work in dead trees where the wood is softer. 102 00:11:58,551 --> 00:12:00,018 There are ants near this tree too, 103 00:12:00,186 --> 00:12:04,122 which the woodpeckers rely on for food in winter. 104 00:12:16,869 --> 00:12:18,803 Not all owls use nest holes. 105 00:12:19,038 --> 00:12:22,201 The eagle owl nests on the ground, among rocks. 106 00:12:23,843 --> 00:12:25,606 It already has a clutch of three eggs, 107 00:12:25,778 --> 00:12:29,475 for, being a permanent resident of these forests, it paired early. 108 00:12:40,259 --> 00:12:42,557 Plants now have their chance to breed. 109 00:12:42,728 --> 00:12:46,528 The wood anemones are already in flower, as are the pines. 110 00:12:46,766 --> 00:12:49,257 Each tree produces male and female flowers, 111 00:12:49,435 --> 00:12:51,926 which mature at different times, 112 00:12:52,104 --> 00:12:56,370 so the female flowers are likely to be fertilised by pollen from other trees. 113 00:12:59,812 --> 00:13:03,373 Now it is as warm as it ever will be in the northern forests. 114 00:13:03,582 --> 00:13:07,313 Summer visitors are arriving, and the trees echo with their song. 115 00:13:13,459 --> 00:13:16,656 This willow warbler, singing so vigorously in Scandinavia, 116 00:13:16,829 --> 00:13:20,230 has come all the way from the savannah country south of the Sahara. 117 00:13:20,666 --> 00:13:21,928 So has the winchat. 118 00:13:24,770 --> 00:13:26,761 And the lure that has brought them so far 119 00:13:26,939 --> 00:13:30,238 is the sudden emergence of myriads of insects. 120 00:13:40,753 --> 00:13:45,315 This bedraggled creature is hardly recognisable, for its wings have not yet expanded. 121 00:13:45,558 --> 00:13:46,957 It's a pine beauty moth, 122 00:13:47,126 --> 00:13:51,654 and its first priority is to leave the forest floo which is full of danger. 123 00:13:52,131 --> 00:13:54,463 But not all the moths have such a clear run. 124 00:14:00,706 --> 00:14:03,038 Shrews are among the first to feed on them. 125 00:14:05,544 --> 00:14:09,036 Up among the pine needles, the pine beauty pumps fluid out of its body 126 00:14:09,215 --> 00:14:11,479 and into the veins of its wings. 127 00:14:20,793 --> 00:14:25,355 Here the moths will lay their eggs so their caterpillars can feed on the young shoots 128 00:14:26,765 --> 00:14:29,233 The wood ants have missed their chance to catch the adult moth, 129 00:14:29,401 --> 00:14:32,393 but now they're looking for the caterpillars among the branches. 130 00:14:34,974 --> 00:14:38,774 The colour and the pattern of the caterpillar conceals it from birds which hunt by sight, 131 00:14:38,944 --> 00:14:43,108 but is no protection against ants which search by smell and touch. 132 00:15:11,310 --> 00:15:15,337 Finally the body is hauled down to the nest for all to consume. 133 00:15:22,588 --> 00:15:26,251 The caterpillars of the sawfly are also swarming on the pine shoots. 134 00:15:26,458 --> 00:15:29,859 They do have a defence against ants: A chemical one. 135 00:15:30,229 --> 00:15:35,667 As they chew, they store some of the resin from the pine needles in a pouch inside their mouth. 136 00:15:36,068 --> 00:15:41,529 When a foraging ant discovers them, they dab a spot of this resin on its head, like th 137 00:15:45,878 --> 00:15:52,408 The resin damages the ant's eyes and antennae, so disorientating it that it can hardly walk. 138 00:15:53,285 --> 00:15:55,048 Even if it finds its way back to the nest, 139 00:15:55,220 --> 00:16:00,783 it smells so strongly and strangely that the other ants treat it as an intruder and kill it 140 00:16:07,032 --> 00:16:09,432 The ants themselves are food for others. 141 00:16:11,904 --> 00:16:16,204 The wryneck is a member of the woodpecker family that has specialised in eating ants, 142 00:16:16,375 --> 00:16:18,775 and particularly relishes their cocoons. 143 00:16:23,849 --> 00:16:29,549 Like its cousins, the wryneck nests in holes in trees, but it doesn't excavate them for itself. 144 00:16:29,788 --> 00:16:33,451 It is yet another tenant of vacated woodpecker holes. 145 00:16:43,569 --> 00:16:48,404 With a long tongue you can even collect insects from the bark without leaving your nest. 146 00:16:51,110 --> 00:16:53,943 Here in the far north, close to the Arctic Circle, 147 00:16:54,113 --> 00:16:58,675 the sun during the summer hardly sinks below the horizon and the nights are brief. 148 00:17:04,957 --> 00:17:09,189 The eagle owl hunts just as effectively in the twilight as in the dark. 149 00:17:09,495 --> 00:17:13,556 It has a rabbit. The season is a good one and game is abundant. 150 00:17:16,268 --> 00:17:19,965 Down in the nest on the forest floor, there is only one chick left. 151 00:17:20,172 --> 00:17:22,572 The other two may have been taken by foxes. 152 00:17:27,246 --> 00:17:32,013 Eagle owls often kill rival species, and this chick's last meal was a short-eared owl, 153 00:17:32,184 --> 00:17:33,674 which it's not yet finished. 154 00:17:35,187 --> 00:17:37,849 The single survivor has a superabundance of food. 155 00:17:38,023 --> 00:17:42,687 It has grown fast and its adult feathers are already appearing through its down. 156 00:17:44,563 --> 00:17:47,396 The tail of a red squirrel is left over from a previous meal, 157 00:17:47,566 --> 00:17:49,466 and it even takes that too. 158 00:18:03,582 --> 00:18:06,176 The voles are swarming on the forest floor. 159 00:18:06,418 --> 00:18:09,251 Last winter, the pines produced great quantities of seed, 160 00:18:09,421 --> 00:18:12,083 so many adult voles survived till spring 161 00:18:12,257 --> 00:18:15,488 and now they're all breeding at an extraordinary rate. 162 00:18:15,661 --> 00:18:18,755 This female produced her four young only three weeks ago, 163 00:18:18,931 --> 00:18:23,959 but she is already pregnant again and will soon abandon this family and start a new one. 164 00:18:50,996 --> 00:18:53,829 All the owls, some visitors, some residents, 165 00:18:53,999 --> 00:18:56,297 scour the forest for voles. 166 00:19:05,444 --> 00:19:11,974 Tengmalm's owl, up in a tree hole, has three chicks, all flourishing and all demanding voles. 167 00:19:41,980 --> 00:19:43,948 The number of voles varies considerably. 168 00:19:44,116 --> 00:19:47,574 It gradually builds up over a period of five to six years 169 00:19:47,753 --> 00:19:53,487 until finally there are so many that they eat out their food supply and the population crashes. 170 00:19:53,959 --> 00:19:56,519 These changes have their effect on the owl population. 171 00:19:56,828 --> 00:19:59,126 More voles mean better-fed owls, 172 00:19:59,298 --> 00:20:02,563 which produce bigger clutches of eggs and rear more chicks. 173 00:20:02,801 --> 00:20:06,794 And as the number of owls increases, so they spread out into new territory. 174 00:20:08,607 --> 00:20:12,202 I'm in Finland, very close to the Russian border. 175 00:20:12,444 --> 00:20:17,074 In fact, those pine forests behind me are actually in Russia. 176 00:20:17,349 --> 00:20:21,786 But the frontier is no barrier to the bird they call the phantom of the north, 177 00:20:21,954 --> 00:20:23,387 the great grey owl, 178 00:20:23,555 --> 00:20:26,547 and in years when the vole population is high, 179 00:20:26,725 --> 00:20:32,857 the owl comes across these frontiers and into the Finnish pine forests. 180 00:20:33,065 --> 00:20:36,091 And I know they are here already because I have just picked up this. 181 00:20:36,268 --> 00:20:38,532 This is an owl pellet. 182 00:20:38,837 --> 00:20:45,936 All owls, as part of their natural digestion, throw up the fur and bones of their prey. 183 00:20:46,144 --> 00:20:50,808 And this, I can see, has actually got vole skulls in it. 184 00:20:50,983 --> 00:20:56,114 But to discover exactly what the state of the vole population is at the moment, 185 00:20:56,288 --> 00:21:03,956 I'll have to look inside the nest of a great grey and to do that I'll need this. 186 00:21:04,630 --> 00:21:11,559 All owls are fairly ferocious and the great grey owl certainly can be, 187 00:21:11,737 --> 00:21:16,436 so as part of the standard equipment of looking for owl nests you need this. 188 00:21:21,179 --> 00:21:26,014 Up there is one of their nests, and the female has just flown off. 189 00:21:26,218 --> 00:21:30,052 She's perching in that tree over there, keeping a very close eye on me. 190 00:21:30,255 --> 00:21:32,450 If I go up and have a look in the nest, 191 00:21:32,624 --> 00:21:37,687 I may be able to get some idea as to how the vole cycle is going. 192 00:21:49,841 --> 00:21:54,505 And... come on... 193 00:21:54,680 --> 00:21:56,910 there is just one chick. 194 00:21:57,149 --> 00:22:01,085 If the voles had been at the height of their population, 195 00:22:01,286 --> 00:22:05,450 there would probably be four chicks in such a nest as this, 196 00:22:05,624 --> 00:22:08,650 but the fact there is only one makes it pretty clear 197 00:22:08,827 --> 00:22:12,593 that the vole population is already beginning to crash. 198 00:22:13,065 --> 00:22:21,495 So it is very likely the female and her mate will soon be on their way back to Russia. 199 00:22:25,777 --> 00:22:29,338 There's now just a month left of the short northern summer. 200 00:22:29,581 --> 00:22:32,914 Many of the birds that came up here to harvest the insects and to breed 201 00:22:33,085 --> 00:22:37,385 will soon be moving back again to avoid the severities of the coming winter. 202 00:22:38,724 --> 00:22:42,990 Some, like the redwing, will go to open pastureland down south. 203 00:22:43,562 --> 00:22:46,053 The brambling prefers beech woodland, 204 00:22:46,231 --> 00:22:49,200 and will leave almost as soon as it has finished its summer moult. 205 00:22:56,174 --> 00:22:58,699 The hawk owl is driven south by hunger, 206 00:22:58,977 --> 00:23:03,641 for as the forest gets colder, there is less food to be found. 207 00:23:04,616 --> 00:23:08,518 As it flies south, so the trees beneath change character. 208 00:23:08,820 --> 00:23:14,190 The ranks of dark conifers are replaced by the brighter green of the broadleaved trees: 209 00:23:14,393 --> 00:23:17,794 Oak and ash, birch and beech. 210 00:23:42,554 --> 00:23:48,515 Down here, the weather's warmer, the summers are longer, and the woodlands are free of frost, 211 00:23:48,693 --> 00:23:52,356 not forjust two or three months in the year, but for eight or nine, 212 00:23:52,664 --> 00:23:54,996 and the shape of the trees is very different. 213 00:23:55,200 --> 00:23:59,432 Instead of their branches drooping down, and so shedding the snow, 214 00:23:59,638 --> 00:24:02,232 these branches spread out widely, 215 00:24:02,441 --> 00:24:07,174 carrying tier upon tier of leaves with which to catch the abundant energy of the sun. 216 00:24:07,412 --> 00:24:09,175 And the leaves are very different. 217 00:24:09,347 --> 00:24:14,216 They are not covered with a thick, protective rind but are thin, delicate structures. 218 00:24:15,320 --> 00:24:17,618 During the summer water is more accessible, 219 00:24:17,789 --> 00:24:21,088 so there is less need to take rigorous measures to conserve it. 220 00:24:21,426 --> 00:24:26,056 Indeed, during hot days the trees evaporate large quantities to keep cool. 221 00:24:26,264 --> 00:24:28,459 So the pores through which they breathe are numerous, 222 00:24:28,633 --> 00:24:31,397 and not in pits as they are in the pines. 223 00:24:35,340 --> 00:24:42,075 These succulent, soft leaves, unlike pine needles, are relished as food by all kinds of creatures. 224 00:24:48,086 --> 00:24:50,452 Large animals, like deer, take many of them, 225 00:24:50,622 --> 00:24:55,321 but the greatest quantity by far is gathered by insects. 226 00:25:20,752 --> 00:25:26,019 The forest canopy in late summer has more birds in it than at any other time of the year. 227 00:25:26,258 --> 00:25:28,954 There are returning migrants newly arrived from the north, 228 00:25:29,127 --> 00:25:33,063 resident breeders gathering food to feed their second families of the season, 229 00:25:33,231 --> 00:25:36,223 and young fledglings starting to forage for themselves 230 00:25:36,401 --> 00:25:39,598 and still not sure what is edible and what isn't. 231 00:25:39,971 --> 00:25:44,874 Nearly all of them are hunting for insects, and the crop they take is huge. 232 00:25:57,656 --> 00:26:01,990 Not surprisingly, the insects have evolved many ways of protecting themselves. 233 00:26:02,193 --> 00:26:06,323 They snip off half-eaten leaves so as to give the minimum sign of their presence. 234 00:26:06,531 --> 00:26:10,194 They disguise themselves as a blob of cuckoo spit or a bird dropping, 235 00:26:10,368 --> 00:26:14,634 but if they move, as eventually they must, their concealment is lost. 236 00:26:25,684 --> 00:26:28,585 Some hang in places which are difficult to reach. 237 00:26:28,887 --> 00:26:35,156 This might baffle a fledgling, but an adult great tit is both experienced and agile. 238 00:26:44,636 --> 00:26:48,094 The tree creeper specialises in insects that live on bark. 239 00:26:52,010 --> 00:26:56,208 A poplar hawk moth tries to defend itself by pretending to be fierce. 240 00:27:10,061 --> 00:27:13,292 The nuthatch habitually works its way down the trunk, 241 00:27:13,498 --> 00:27:16,023 and that way may see insects that have been overlooked 242 00:27:16,201 --> 00:27:18,931 by tree creepers that habitually come up it. 243 00:27:37,055 --> 00:27:39,216 One of the most expert of all bark-feeders, 244 00:27:39,391 --> 00:27:44,124 and in some ways the most specialised of all the birds living in the tall trees of these forest 245 00:27:44,295 --> 00:27:45,853 are the woodpeckers. 246 00:27:46,398 --> 00:27:48,832 The greater spotted woodpecker is typical of them. 247 00:27:49,000 --> 00:27:51,833 Its hearing is excellent and it locates the grubs it seeks 248 00:27:52,003 --> 00:27:55,962 by the tiny sounds they make as they move inside the bark. 249 00:27:59,310 --> 00:28:03,804 Its tall feathers have strong quills and serve as props for its body. 250 00:28:04,783 --> 00:28:09,948 Its bill has a resilient pad at the base which cushions its brain from the shock of its drilling. 251 00:28:12,624 --> 00:28:18,529 Its feet give it a grip in all directions, with two toes pointing forwards and two backwards. 252 00:28:19,364 --> 00:28:22,060 Each continent has its own range of woodpeckers. 253 00:28:22,300 --> 00:28:23,665 Europe has ten species, 254 00:28:23,835 --> 00:28:27,430 but here in North America there are over twice as many. 255 00:28:27,806 --> 00:28:32,834 This one, a sapsucker, drills holes in trees not for insects, but for sap. 256 00:28:33,244 --> 00:28:36,577 It digs lines of these wells in many kinds of trees. 257 00:28:37,115 --> 00:28:41,176 Each little hole points slightly downwards so that the sap does not trickle out 258 00:28:41,352 --> 00:28:43,684 but collects in a small pool inside, 259 00:28:43,888 --> 00:28:46,152 and the sapsucker collects it with its tongue. 260 00:28:46,825 --> 00:28:48,087 And so do other birds. 261 00:28:52,964 --> 00:28:53,988 A hummingbird. 262 00:28:54,165 --> 00:28:57,134 Most of its family live in the tropics and feed on nectar, 263 00:28:57,368 --> 00:29:02,465 but this one comes north in the summer and finds tree sap just as acceptable. 264 00:29:04,175 --> 00:29:06,769 Flies, too, come to the sweet sap. 265 00:29:23,194 --> 00:29:27,290 In late summer, the parent sapsuckers lead their fledglings to the wells 266 00:29:27,465 --> 00:29:32,198 and leave them to feast not only on the sap but on the insects it attracts 267 00:29:34,973 --> 00:29:41,037 This American woodpecker uses its drilling skills to bore neat sockets in dead tree trunks. 268 00:29:41,713 --> 00:29:44,477 Acorns are its main food, but during the season, 269 00:29:44,649 --> 00:29:47,743 there are far more acorns than the woodpeckers can eat immediately. 270 00:29:48,219 --> 00:29:49,777 But they don't leave them for others. 271 00:29:50,088 --> 00:29:54,354 Several birds share a communal acorn treasury, like this one. 272 00:29:54,659 --> 00:29:59,221 They hammer the acorns into the holes so firmly that few other creatures can get them out, 273 00:29:59,397 --> 00:30:04,232 and the store will keep the acorn woodpeckers supplied throughout the year. 274 00:30:10,341 --> 00:30:14,641 The ripening acorns herald the end of summer and the beginning of autumn. 275 00:30:14,946 --> 00:30:18,279 Trees and bushes proffer their seeds to the forest animals. 276 00:30:18,516 --> 00:30:21,007 Some are wrapped in soft and tasty flesh 277 00:30:21,186 --> 00:30:25,213 to tempt the animals to eat them and so transport them to new sites. 278 00:30:27,091 --> 00:30:28,581 Others are packed with nourishment, 279 00:30:28,760 --> 00:30:32,321 not for animals, but to provide food for the germinating seedling, 280 00:30:32,497 --> 00:30:34,522 but the animals eat them just the same. 281 00:30:35,099 --> 00:30:41,197 Even the hard and unpromising-Iooking acorns of the American pin oak are collected by racoons. 282 00:30:50,915 --> 00:30:56,581 The squirrel's habit of burying acorns for a winte store has been the start of many an oak. 283 00:30:59,057 --> 00:31:03,892 The black bear, on occasion, will eat fish and voles and even carrion, 284 00:31:04,062 --> 00:31:06,189 but much of its diet is vegetable. 285 00:31:06,664 --> 00:31:08,825 It will dig for roots and even eat pine cones, 286 00:31:09,000 --> 00:31:13,403 but it has a very sweet tooth and just now it relishes the fruit. 287 00:31:28,119 --> 00:31:31,816 All sorts of mammals are now clambering around in the trees in search of fruit. 288 00:31:31,990 --> 00:31:34,857 The possum, a strange primitive animal of the Americas 289 00:31:35,026 --> 00:31:39,224 related more closely to kangaroos than to rats, eats almost anything. 290 00:31:43,835 --> 00:31:47,669 Few of them can get to the very tops of the trees or the thinnest twig, 291 00:31:47,839 --> 00:31:49,602 but a chipmunk can. 292 00:31:53,478 --> 00:31:56,379 The chills of autumn presage the coming of winter. 293 00:31:56,981 --> 00:32:00,439 The delicate leaves worked efficiently throughout the warm moist summer, 294 00:32:00,618 --> 00:32:02,552 but they are not suited to cold weather. 295 00:32:03,021 --> 00:32:04,420 Frost will damage them. 296 00:32:04,856 --> 00:32:07,051 Their abundant pores would lose too much water. 297 00:32:07,292 --> 00:32:11,388 So the green chlorophyll in them is broken down and withdrawn into the tree, 298 00:32:11,562 --> 00:32:14,554 revealing the red and brown waste products, 299 00:32:14,832 --> 00:32:16,697 and the leaves fall. 300 00:32:18,136 --> 00:32:21,367 And they, too, provide food for another woodland community, 301 00:32:21,539 --> 00:32:23,939 the inhabitants of the leaf litter. 302 00:32:27,345 --> 00:32:31,748 There may be 100,000 box mites in every cubic yard. 303 00:32:32,784 --> 00:32:34,376 And there are many other creatures too, 304 00:32:34,552 --> 00:32:36,611 chewing their way through the dead leaves, 305 00:32:36,788 --> 00:32:38,881 extracting what nutriment they can 306 00:32:39,057 --> 00:32:43,016 and leaving the remainder to be dealt with by fungi and bacteria. 307 00:32:50,501 --> 00:32:53,061 They themselves are hunted by monsters in miniature, 308 00:32:53,237 --> 00:32:54,727 pseudoscorpions, 309 00:32:55,006 --> 00:33:00,069 horrific in close-up, but, perhaps fortunately, the size of a pinhead. 310 00:33:36,247 --> 00:33:41,310 Snails are giants in comparison and, since they carry their shells around with them, 311 00:33:41,486 --> 00:33:46,150 they might seem to be fairly well protected against any creatures smaller than a bird. 312 00:33:46,657 --> 00:33:50,923 But one particular beetle has specialised equipment for dealing with them. 313 00:33:53,064 --> 00:33:55,965 Its head and jaws are long and thin. 314 00:34:23,594 --> 00:34:26,085 Almost hidden in the leaves of these American woods 315 00:34:26,264 --> 00:34:30,758 are some spectacularly coloured little creatures hardly bigger than worms. 316 00:34:34,772 --> 00:34:37,206 They are amphibians: Salamanders. 317 00:34:37,508 --> 00:34:42,639 Almost every mountain range in the US has its own species with its own colours, 318 00:34:42,814 --> 00:34:45,282 but, being nocturnal, they're rarely seen. 319 00:35:06,604 --> 00:35:11,268 Shrews eat most small living things they come across, and they are formidable hunters, 320 00:35:11,442 --> 00:35:14,240 for they are one of the few mammals that has a poisonous bite. 321 00:35:20,852 --> 00:35:25,721 The salamander's only defence is to produce an acrid liquid from glands on its tail 322 00:35:26,157 --> 00:35:30,787 The first time a shrew encounters this, it usually takes no notice and eats the salamander, 323 00:35:30,962 --> 00:35:33,021 but apparently the taste is not very nice, 324 00:35:33,197 --> 00:35:35,461 for on later encounters, like this one, 325 00:35:35,633 --> 00:35:38,898 one sniff reminds the shrew the meal won't be a good one 326 00:35:39,070 --> 00:35:41,561 and it leaves the salamander alone. 327 00:35:48,212 --> 00:35:50,578 The summer visitors have departed. 328 00:35:51,182 --> 00:35:52,672 The woods have fallen silent. 329 00:35:52,917 --> 00:35:56,546 The days are shortening and the temperature falling. 330 00:36:27,518 --> 00:36:31,784 Eventually the land is gripped tight by frost. 331 00:36:57,982 --> 00:36:59,040 It's late winter. 332 00:36:59,250 --> 00:37:02,310 The once-resplendent trees are now mere skeletons 333 00:37:02,486 --> 00:37:06,946 and life in these woodlands has come almost to a standstill. 334 00:37:07,158 --> 00:37:09,956 The trees, without their leaves, can't grow. 335 00:37:10,194 --> 00:37:14,824 The birds that came visiting up here during the summer have now retreated south, 336 00:37:15,066 --> 00:37:20,163 and some of these small mammals have crawled into holes and gone to sleep. 337 00:37:20,404 --> 00:37:25,501 Their heartbeat has almost stopped, their bodies have become as cold as stone. 338 00:37:25,743 --> 00:37:27,040 They're hibernating. 339 00:37:27,278 --> 00:37:31,112 But that sleep doesn't last throughout the winter. 340 00:37:31,282 --> 00:37:34,843 They wake up every four or five days and go and look for food. 341 00:37:35,086 --> 00:37:38,112 Like, for example, those small chipmunks over there. 342 00:37:39,156 --> 00:37:42,023 Not only warmth but intense cold will bring them out, 343 00:37:42,226 --> 00:37:45,195 for although their body temperature falls while they hibernate, 344 00:37:45,363 --> 00:37:48,025 if it drops to freezing point, they will die. 345 00:37:48,299 --> 00:37:52,633 So in really cold spells, they must get up and warm themselves with a little exercise, 346 00:37:52,803 --> 00:37:55,931 even though it dangerously depletes their fat reserves. 347 00:37:57,608 --> 00:38:01,100 But in these American woodlands there is one spectacular sleeper 348 00:38:01,279 --> 00:38:03,270 who dozes for months on end. 349 00:38:05,149 --> 00:38:06,275 Just look at this. 350 00:38:13,724 --> 00:38:15,214 A black bear. 351 00:38:17,628 --> 00:38:21,462 She retired to this den in early autumn, and after a month or so of drowsiness, 352 00:38:21,632 --> 00:38:22,826 produced her cubs. 353 00:38:23,067 --> 00:38:27,527 In the colder northern parts of these woods, she may spend six or seven months here, 354 00:38:27,705 --> 00:38:29,605 during which time she suckles her cubs 355 00:38:29,774 --> 00:38:33,574 but neither feeds herself nor urinates nor defecates. 356 00:38:33,844 --> 00:38:37,041 So she spends the majority of her life half-asleep. 357 00:38:40,084 --> 00:38:45,579 When spring at last comes, the brown carpet of rotting leaves is suddenly flooded with colour. 358 00:38:48,859 --> 00:38:52,727 The plants that live close to the ground now make haste to sprout and flower 359 00:38:52,897 --> 00:38:54,489 and soak up the spring sunshine 360 00:38:54,665 --> 00:38:58,726 before the trees above produce their own leaves and cut out the light. 361 00:39:03,174 --> 00:39:04,641 The bear's den is empty, 362 00:39:04,809 --> 00:39:07,403 but the owners haven't gone far. 363 00:39:17,088 --> 00:39:19,784 There's still not much to eat, only a few leaves, 364 00:39:19,957 --> 00:39:23,120 nor will there be until the first of the berries come into fruit in summer, 365 00:39:23,294 --> 00:39:26,058 but meanwhile at least the sun is warm. 366 00:39:32,870 --> 00:39:35,304 Another mother spends the spring up in a tree: 367 00:39:35,473 --> 00:39:38,374 A wood duck, only she is about to leave. 368 00:39:45,383 --> 00:39:47,351 The hole has provided a secure nest, 369 00:39:47,518 --> 00:39:51,045 but all ducklings follow their mothers as soon as they hatch. 370 00:40:23,154 --> 00:40:27,648 And now new forms appear from among the dead leaves. 371 00:41:02,993 --> 00:41:04,927 The spring showers soak the woodlands 372 00:41:05,095 --> 00:41:09,122 and create just the moist, warm conditions needed by the fungi 373 00:41:09,300 --> 00:41:11,427 to produce their fruiting bodies. 374 00:41:11,936 --> 00:41:15,428 These must be mature and ready to discharge their microscopic spores 375 00:41:15,606 --> 00:41:18,666 by the time the dry winds of summer begin to blow, 376 00:41:18,876 --> 00:41:23,108 so that their spores, like dust, will be carried all through the forest. 377 00:41:25,850 --> 00:41:29,684 Once, the woods of North America stretched over the eastern half of the continent 378 00:41:29,854 --> 00:41:33,722 in an almost continuous band hundreds of miles deep. 379 00:41:34,325 --> 00:41:38,523 Today, the majority has been felled to make space for farmland and cities, 380 00:41:38,696 --> 00:41:41,824 but enough remains to make plain their splendour. 381 00:41:45,135 --> 00:41:47,569 And now we've come farther south still. 382 00:41:47,771 --> 00:41:52,174 I'm on the borders of Florida and Georgia in the southern United States, 383 00:41:52,343 --> 00:41:56,336 and here it's very hot in the summer and the winters are very mild, 384 00:41:56,514 --> 00:41:59,278 with only a few frosts, and none of them severe. 385 00:41:59,517 --> 00:42:06,081 So some of the broadleaved trees here, like this oak, don't shed all their leaves in the autum 386 00:42:06,257 --> 00:42:10,125 but keep them throughout the year and continue growing. 387 00:42:10,661 --> 00:42:13,926 And these aren't the only evergreens that are here, either. 388 00:42:14,164 --> 00:42:15,791 There are pines. 389 00:42:16,100 --> 00:42:20,662 In some parts where the soil is very rocky or sandy and poor in nutrients, 390 00:42:20,838 --> 00:42:24,296 the pines will grow because nothing else can survive there. 391 00:42:24,575 --> 00:42:29,444 But this pine forest owes its existence to another factor altogether. 392 00:42:40,157 --> 00:42:43,558 Oak saplings are killed within minutes by fire. 393 00:42:46,063 --> 00:42:50,557 But the terminal buds of young pines are surrounded by a shock of needles. 394 00:42:50,868 --> 00:42:55,896 They burn at a relatively low temperature, and by the time the flames have consumed them, 395 00:42:56,073 --> 00:42:57,938 the main fire has swept by 396 00:42:58,108 --> 00:43:03,569 and the bud at the top of the stem, from which new growth will come, is still unharmed. 397 00:43:06,050 --> 00:43:11,454 Fires like these are notjust the work of careless people, they occur naturally. 398 00:43:11,989 --> 00:43:16,016 The spark that regularly sets fire to these forest is lightning. 399 00:43:16,226 --> 00:43:19,559 In this part of the southern States, violent thunderstorms are common 400 00:43:19,730 --> 00:43:22,198 and lightning often strikes the taller trees, 401 00:43:22,366 --> 00:43:27,099 scoring a deep groove down the length of the trunk as it flashes down to earth. 402 00:43:30,074 --> 00:43:34,534 And this at my feet is the tinder which set it aflame. 403 00:43:34,778 --> 00:43:40,148 These are pine needles, and they're so full of resin and they're so dry 404 00:43:40,317 --> 00:43:42,478 that they flame up very easily. 405 00:43:42,653 --> 00:43:46,783 But the fire they produce is not very hot, and it's also very short-lived, 406 00:43:46,957 --> 00:43:51,257 so that if any creature can survive fire forjust one or two minutes, 407 00:43:51,428 --> 00:43:54,625 then it can survive a fire like this. 408 00:43:57,468 --> 00:44:00,335 The rattlesnake, like many other ground-living animals, 409 00:44:00,504 --> 00:44:03,701 regularly takes refuge from the midday sun in holes, 410 00:44:03,907 --> 00:44:07,673 so now it knows exactly where to go to escape the fire. 411 00:44:24,595 --> 00:44:28,463 But this hole is already occupied by its digger and owner, 412 00:44:32,169 --> 00:44:33,830 a gopher tortoise. 413 00:44:48,519 --> 00:44:53,013 Rattlesnake and tortoise do not normally interfere with one another... 414 00:45:05,969 --> 00:45:09,063 ...and that seems to be the way things are going to stay. 415 00:45:11,542 --> 00:45:15,569 But in the back of the burrow lies another refugee, an indigo snake, 416 00:45:15,746 --> 00:45:18,909 and it, on occasion, eats rattlesnakes. 417 00:45:40,304 --> 00:45:44,866 But the fire is passing and the rattlesnake can return to the forest. 418 00:45:51,148 --> 00:45:54,549 Some insects don't avoid fire, they actively seek it. 419 00:45:54,752 --> 00:45:57,346 Beetles find it difficult to lay their eggs in the pines 420 00:45:57,521 --> 00:45:59,751 because the trees swamp them with resin. 421 00:45:59,957 --> 00:46:03,085 But a tree killed by fire can't resist, 422 00:46:03,293 --> 00:46:05,955 and these beetles take advantage of the situation. 423 00:46:06,263 --> 00:46:09,994 They have pits behind their legs which are sensitive to infra-red rays, 424 00:46:10,167 --> 00:46:13,000 and therefore they can detect the slightest rise in temperature, 425 00:46:13,170 --> 00:46:17,698 and with these to guide them, they travel from all over the forest to the wake of the fire 426 00:46:17,875 --> 00:46:19,740 and arrive in hundreds. 427 00:46:24,648 --> 00:46:26,172 Quickly they mate. 428 00:46:32,389 --> 00:46:34,789 The females crawl all over the scorched trunks, 429 00:46:34,958 --> 00:46:38,052 seeking crevices in the bark into which they can lay their eggs, 430 00:46:38,228 --> 00:46:42,790 so ensuring that their grubs will have some nice nutritious bark to chew. 431 00:46:45,369 --> 00:46:47,303 As insects assemble in the burnt forest, 432 00:46:47,471 --> 00:46:49,405 the insect-eaters follow. 433 00:46:49,973 --> 00:46:53,909 The oak toad almost exactly matches the colour of the charred forest floor. 434 00:46:56,647 --> 00:47:00,606 Other more conspicuous hunters wait on newly emerged shoots. 435 00:47:06,690 --> 00:47:10,148 Within a couple of months of a summer fire, the forest has more than recovered, 436 00:47:10,327 --> 00:47:12,022 it is rejuvenated. 437 00:47:12,196 --> 00:47:14,664 The fire has cleared away the old growth on the ground, 438 00:47:14,832 --> 00:47:19,701 and by reducing the pine needles to ash has released their nutrients into the soil, 439 00:47:19,937 --> 00:47:24,033 and now the ground sprouts more flowers than at any other time. 440 00:47:37,254 --> 00:47:41,748 Because of regular fires, big bushes can't establish themselves here, 441 00:47:41,992 --> 00:47:47,020 so swampy areas are not colonised and sucked dry by them as happens elsewhere, 442 00:47:47,264 --> 00:47:50,199 and open marshes remain where pitcher plants can grow 443 00:47:50,367 --> 00:47:53,063 and where frogs can swim and breed. 444 00:47:53,337 --> 00:47:59,742 Indeed, one species of frog lives nowhere else but in these pools in the American pine barrens. 445 00:48:16,159 --> 00:48:20,960 The woodpeckers here can't excavate their nest in dead trees as do woodpeckers elsewhere, 446 00:48:21,131 --> 00:48:24,828 for in this fire-ravaged forest they would risk incineration, 447 00:48:25,002 --> 00:48:29,564 so the red-cockaded woodpecker drills its holes in living pines. 448 00:48:29,973 --> 00:48:35,172 But the wood is so hard, it takes several woodpeckers about two years to dig the hole. 449 00:48:37,781 --> 00:48:42,809 Resinous sap seeps out around the hole where the outer layers of the tree have been breached. 450 00:48:43,053 --> 00:48:45,817 So the birds make their hole low down on the trunk 451 00:48:45,989 --> 00:48:50,790 where the inner sap-free heartwood is thick enough to accommodate the entire nest. 452 00:48:51,895 --> 00:48:54,159 The flow of resin is diverted to the outside 453 00:48:54,331 --> 00:48:58,290 by drilling pits like sap wells above and below the hole. 454 00:49:05,008 --> 00:49:10,640 It's in these laboriously excavated holes that the red-cockaded woodpecker raises its young. 455 00:49:18,355 --> 00:49:23,315 The holes are very conspicuous, for each is surrounded by a sheet of yellow congealed resin. 456 00:49:26,830 --> 00:49:31,426 The rat snake is a great robber of nests and stealer of chicks. 457 00:49:45,582 --> 00:49:48,415 It's an extremely skilful tree climber. 458 00:49:48,719 --> 00:49:53,019 Since the woodpecker's hole in the living tree has to be fairly low down on the trunk, 459 00:49:53,357 --> 00:49:59,023 it is within easy reach of the snake and therefore might seem to be in considerable danger. 460 00:49:59,663 --> 00:50:02,188 But now the other function of all that resin, 461 00:50:02,366 --> 00:50:05,130 deliberately produced around the nest by the woodpecker, 462 00:50:05,302 --> 00:50:07,031 is about to become clear. 463 00:50:36,400 --> 00:50:39,995 The chemicals in the resin seem to irritate the snake beyond endurance, 464 00:50:40,170 --> 00:50:42,297 and it arches its body away. 465 00:50:45,542 --> 00:50:47,476 Eventually it's too much. 466 00:50:51,314 --> 00:50:56,217 So fire, one way or another, influences the whole community of animals and plants 467 00:50:56,386 --> 00:50:58,513 in the pine forests of the south. 468 00:51:00,190 --> 00:51:06,459 This injury was also caused by fire, and this is also a coniferous tree, 469 00:51:06,696 --> 00:51:08,425 but a very different one. 470 00:51:08,732 --> 00:51:18,607 To start with, it's over 40 feet across along its base and it's 267-1/2 feet high. 471 00:51:18,975 --> 00:51:21,842 This is a giant sequoia. 472 00:51:23,413 --> 00:51:27,679 It's thought to be about 2,500 years old, 473 00:51:27,884 --> 00:51:34,289 but the largest individual tree of all is this one known as the General Sherman. 474 00:51:34,624 --> 00:51:41,154 It's just taller and it's estimated to weigh 1,385 tons, 475 00:51:41,398 --> 00:51:45,528 which makes it the most massive living organism in the world. 476 00:51:47,404 --> 00:51:51,500 Although these trees are growing almost as far south as the southern pines, 477 00:51:51,675 --> 00:51:55,634 the climate here, 2,000 metres up in the Sierra Nevada mountains, 478 00:51:55,812 --> 00:52:00,340 is much colder and snow lies on the ground for almost half the year. 479 00:52:00,717 --> 00:52:02,514 It's as though, by climbing to this height, 480 00:52:02,686 --> 00:52:06,349 we have returned climatically to the great forests of the north. 481 00:52:06,590 --> 00:52:10,617 During the Ice Age, these sequoias grew over much of North America. 482 00:52:10,861 --> 00:52:14,422 But when, some 8,000 years ago, the earth began to warm, 483 00:52:14,598 --> 00:52:19,695 they died out except for these isolated groups high up in the mountains. 484 00:52:27,644 --> 00:52:31,080 We've travelled some 2,000 miles southwards 485 00:52:31,248 --> 00:52:35,378 since we started at the tree line near the Arctic Circle, 486 00:52:35,685 --> 00:52:41,521 and in all that vast territory the majority of the forest trees have been conifers, 487 00:52:41,791 --> 00:52:48,128 so it seems only right and proper that we should end with these, the noblest of them all. 488 00:52:48,398 --> 00:52:51,526 As a group, the conifers owe much of their success 489 00:52:51,701 --> 00:52:55,865 to their ability to cope with the changeable northern climate. 490 00:52:56,106 --> 00:53:00,634 They can survive both the short, dark days of winter with their bitter cold, 491 00:53:00,810 --> 00:53:05,213 as well as the long sunny days of summer with their raging fires. 492 00:53:05,482 --> 00:53:10,317 But if we continue a further 1,000 miles southwards, we come to the tropics, 493 00:53:10,520 --> 00:53:13,648 and there the climate is radically different. 494 00:53:13,857 --> 00:53:16,724 It's no longer very variable but remarkably constant, 495 00:53:16,893 --> 00:53:22,456 with much the same amounts of light and rain and heat throughout the year. 496 00:53:22,699 --> 00:53:28,228 There the other great group of forest trees, the broadleaved trees, come into their own. 497 00:53:28,438 --> 00:53:33,000 That is the jungle, and that's where we'll be in the next programme.