1 00:00:00,800 --> 00:00:02,960 Last time, we brought you winter. 2 00:00:03,040 --> 00:00:04,080 [HOWLING] 3 00:00:04,160 --> 00:00:06,800 Wildlife struggled in freezing temperatures. 4 00:00:06,880 --> 00:00:07,880 [BEAR GROWLING] 5 00:00:09,240 --> 00:00:11,840 Now, spring is here. 6 00:00:11,920 --> 00:00:14,600 Life is about to change, 7 00:00:14,680 --> 00:00:16,720 but not always for the better. 8 00:00:23,040 --> 00:00:25,680 The thaw will melt the snow in the mountains 9 00:00:25,760 --> 00:00:29,080 and cause over one million tons of melt water 10 00:00:29,160 --> 00:00:31,360 to crash through Yellowstone. 11 00:00:35,480 --> 00:00:38,520 Only the strongest animals will survive. 12 00:00:45,840 --> 00:00:49,560 Welcome to Yellowstone, The Toughest Spring. 13 00:01:05,240 --> 00:01:07,280 [BIRD CHIRPING] 14 00:01:07,360 --> 00:01:11,000 It's the end of April and seven degrees Celsius. 15 00:01:15,400 --> 00:01:17,480 The thaw is well underway. 16 00:01:24,760 --> 00:01:27,520 Spring has come to Yellowstone. 17 00:01:27,600 --> 00:01:30,440 Mammals big and small are emerging from their dens, 18 00:01:30,520 --> 00:01:32,760 birds are courting and nesting, 19 00:01:32,840 --> 00:01:35,120 the days are getting longer and warmer. 20 00:01:35,520 --> 00:01:38,480 Now, you may think that life is going to get easier. 21 00:01:39,600 --> 00:01:42,120 Yellowstone is bursting into life. 22 00:01:42,280 --> 00:01:43,920 [HUMMINGBIRD BUZZING] 23 00:01:44,280 --> 00:01:48,360 Humming birds return after spending their winter in the warm south. 24 00:01:51,160 --> 00:01:54,520 Moose feast on the first green shoots. 25 00:01:55,240 --> 00:01:56,600 [SINGING] 26 00:02:01,800 --> 00:02:04,720 Bison migrate back to their calving grounds. 27 00:02:10,560 --> 00:02:13,480 We're in the north-west of the USA, 28 00:02:13,560 --> 00:02:16,280 2,000 metres high up in the Rockies. 29 00:02:18,560 --> 00:02:21,480 Known as the Greater Yellowstone Ecosystem, 30 00:02:21,560 --> 00:02:24,120 it's an area the size of Scotland, 31 00:02:24,200 --> 00:02:26,560 includes two national parks, 32 00:02:26,640 --> 00:02:30,040 and is bounded on three sides by mountain ranges. 33 00:02:32,640 --> 00:02:34,160 Biologist Patrick Aryee 34 00:02:34,240 --> 00:02:37,280 is at the southern end of Greater Yellowstone, 35 00:02:37,360 --> 00:02:41,600 catching up with one species that faces its greatest challenge in spring. 36 00:02:43,720 --> 00:02:46,040 Behind me are the Teton mountains, 37 00:02:46,120 --> 00:02:48,760 and this is the Snake River, 38 00:02:48,880 --> 00:02:51,800 home to North America's largest rodent, the beaver. 39 00:02:53,080 --> 00:02:56,240 There are 15 of them living on this stretch of river, 40 00:02:56,320 --> 00:02:58,880 and they've built this enormous dam. 41 00:03:00,040 --> 00:03:03,440 I can't believe that this dam is not a man-made structure, 42 00:03:03,520 --> 00:03:05,120 and that it's been made by beavers. 43 00:03:05,200 --> 00:03:08,000 I mean, it's...incredible! 44 00:03:08,120 --> 00:03:11,920 Look at the size of these branches, 45 00:03:12,000 --> 00:03:15,520 and even, here we go, these huge rocks as well. 46 00:03:15,600 --> 00:03:19,400 It acts as a way to slow down the waterways, 47 00:03:19,480 --> 00:03:21,400 like speed bumps almost. 48 00:03:21,480 --> 00:03:25,720 But I gotta say that they are nature's most incredible engineers. 49 00:03:27,480 --> 00:03:30,960 But at this time of year, their dam is in real danger. 50 00:03:33,240 --> 00:03:36,560 Soon enough, all that snow is gonna melt 51 00:03:36,640 --> 00:03:39,120 and all that melt water is gonna start flowing down 52 00:03:39,200 --> 00:03:40,600 into these river systems. 53 00:03:40,720 --> 00:03:45,040 And as that water starts to flow and cascade along this river, 54 00:03:45,160 --> 00:03:48,600 it could damage and even destroy not only the dam, 55 00:03:48,680 --> 00:03:50,080 but also the lodge. 56 00:03:50,680 --> 00:03:53,440 And the lodge is where the beavers have been holed up 57 00:03:53,520 --> 00:03:55,520 for the last five months. 58 00:03:56,280 --> 00:03:58,000 Now, we've got a camera rig set up, 59 00:03:58,080 --> 00:04:01,920 so we can actually see exactly what's going on inside there 60 00:04:02,000 --> 00:04:03,160 right now. 61 00:04:03,640 --> 00:04:05,120 If I come over here... 62 00:04:08,760 --> 00:04:10,720 That is incredible. 63 00:04:12,080 --> 00:04:14,640 Oh, they're just starting to wake up. 64 00:04:14,720 --> 00:04:15,920 [GROANS] 65 00:04:19,560 --> 00:04:20,840 In this lodge we've got... 66 00:04:21,200 --> 00:04:23,000 There's two yearlings in there, 67 00:04:23,080 --> 00:04:26,160 two two-year-olds, and then, one adult. 68 00:04:26,240 --> 00:04:28,920 There should be another one, but I can't see it. 69 00:04:30,160 --> 00:04:31,920 This is our beaver family, 70 00:04:32,000 --> 00:04:34,920 and we're gonna be getting to know them very well. 71 00:04:35,520 --> 00:04:36,880 [MOANING] 72 00:04:37,400 --> 00:04:39,520 And we'll be following them over the coming months 73 00:04:39,600 --> 00:04:42,440 to see how they cope when the spring floods hit. 74 00:04:43,400 --> 00:04:45,240 Just seen one dive. 75 00:04:47,920 --> 00:04:51,200 Beavers are most comfortable in water. 76 00:04:51,280 --> 00:04:55,040 Their lumbering bodies are quite ungainly on land. 77 00:04:55,840 --> 00:04:57,920 He's huge! 78 00:04:58,600 --> 00:05:02,120 This stretch of river is home to 15 beavers. 79 00:05:02,200 --> 00:05:06,840 In April, the riverbank is usually covered in a blanket of snow, 80 00:05:06,920 --> 00:05:09,280 so the beavers stay snuggled in their den. 81 00:05:10,440 --> 00:05:13,880 But this year, the snow has already disappeared. 82 00:05:13,960 --> 00:05:17,840 According to scientists, the thaw is three weeks early. 83 00:05:18,480 --> 00:05:21,040 That means the beavers can start venturing out 84 00:05:21,120 --> 00:05:23,920 on the search for new green shoots. 85 00:05:25,080 --> 00:05:26,160 This is brilliant. 86 00:05:26,240 --> 00:05:28,880 I'm just following this beaver, and hopefully, 87 00:05:28,960 --> 00:05:31,960 I'll get to see him when he comes up onto this next dam. 88 00:05:34,640 --> 00:05:38,440 This beaver hasn't eaten fresh food for five months. 89 00:05:43,280 --> 00:05:48,000 Over winter, the beaver's food supply is locked in snow and ice. 90 00:05:50,840 --> 00:05:55,840 They feed on twigs, leaves and bark of aspen and willow trees. 91 00:05:56,400 --> 00:05:58,400 But when there's so much snow on the ground, 92 00:05:58,480 --> 00:06:00,160 they can't get to it. 93 00:06:00,240 --> 00:06:02,080 Yet beavers don't hibernate, 94 00:06:02,560 --> 00:06:05,800 so must keep eating throughout the winter to survive. 95 00:06:07,520 --> 00:06:10,200 Their solution is ingenious. 96 00:06:12,520 --> 00:06:15,320 They collect a mound of twigs and vegetation 97 00:06:15,400 --> 00:06:17,720 big enough to last for five months 98 00:06:17,840 --> 00:06:20,840 and store it by the underwater entrance to their home. 99 00:06:21,520 --> 00:06:23,720 Even when the river freezes over, 100 00:06:23,800 --> 00:06:26,640 they have a larder just a moment's swim away. 101 00:06:30,760 --> 00:06:32,440 But by the end of winter, 102 00:06:32,520 --> 00:06:34,880 the rotten twigs have lost most of their protein. 103 00:06:36,040 --> 00:06:39,560 This beaver is surviving on his own body fat. 104 00:06:41,680 --> 00:06:44,880 The early thaw, however, has given him a lifeline. 105 00:06:45,880 --> 00:06:50,680 This year, he can forage for fresh food three weeks earlier than normal. 106 00:06:55,240 --> 00:06:58,160 It's just what his hungry family needs. 107 00:07:01,200 --> 00:07:03,920 Okay, that adult is now back inside the lodge... 108 00:07:04,000 --> 00:07:05,400 [BEAVER PUPS YELPING] 109 00:07:06,200 --> 00:07:08,720 And it's got a mouthful of vegetation. 110 00:07:09,000 --> 00:07:10,800 [BEAVER PUPS YELPING] 111 00:07:12,080 --> 00:07:15,800 These beavers have lost a third of their body weight over winter. 112 00:07:15,880 --> 00:07:16,920 To gain that weight back, 113 00:07:17,320 --> 00:07:19,960 they'll need to eat a kilogram of twigs and leaves 114 00:07:20,040 --> 00:07:21,480 every single day. 115 00:07:23,680 --> 00:07:26,680 The younger beavers squeak to demand food, 116 00:07:26,760 --> 00:07:29,760 but when competition is this fierce 117 00:07:29,840 --> 00:07:31,920 it's every beaver for itself. 118 00:07:32,000 --> 00:07:33,560 [AGGRESSIVE SQUEAKING] 119 00:07:42,320 --> 00:07:46,320 In spring, twigs are rich in sugars and proteins, 120 00:07:46,400 --> 00:07:49,480 just what they need to kick start their recovery. 121 00:07:50,080 --> 00:07:51,760 But to reach the fresh food, 122 00:07:51,840 --> 00:07:54,880 the beavers must first get to work. 123 00:07:57,640 --> 00:08:01,120 Not only are beavers phenomenal engineers 124 00:08:01,200 --> 00:08:02,680 building all those dams, 125 00:08:02,760 --> 00:08:05,160 but they're also professional lumberjacks 126 00:08:05,240 --> 00:08:08,480 and they can take down whole trees, just like this one, 127 00:08:08,560 --> 00:08:11,160 and they do that using their super sharp teeth. 128 00:08:11,560 --> 00:08:14,360 These bottom teeth are just like chisels 129 00:08:14,440 --> 00:08:17,000 and what they'll do is, get their head in sideways 130 00:08:17,080 --> 00:08:19,320 and chew away at the bark. 131 00:08:19,400 --> 00:08:21,640 With smaller trees, they'll go right the way through 132 00:08:21,720 --> 00:08:23,040 and you'll often see beavers running away 133 00:08:23,120 --> 00:08:25,040 just before the trees fall down, 134 00:08:25,120 --> 00:08:26,880 but with big ones like this one, 135 00:08:26,960 --> 00:08:29,920 they'll only get so far and then they'll move away 136 00:08:30,000 --> 00:08:31,720 and let the wind do the rest of the job 137 00:08:31,800 --> 00:08:33,160 [CREAKING AND CRACKING] 138 00:08:34,680 --> 00:08:35,800 [THUDS] 139 00:08:35,880 --> 00:08:38,640 Now, this is a really big tree, 140 00:08:38,720 --> 00:08:41,320 but the part the beavers are really interested in 141 00:08:41,400 --> 00:08:43,360 is up here, the top third, 142 00:08:43,440 --> 00:08:46,720 and I see where they've gnawed away at this end 143 00:08:46,800 --> 00:08:49,360 and hauled all the branches back to the river 144 00:08:49,440 --> 00:08:51,400 to construct their lodge and the dams. 145 00:08:52,280 --> 00:08:54,480 And making sure their dams are re-enforced 146 00:08:54,560 --> 00:08:56,960 before the spring floods hit is crucial. 147 00:09:00,040 --> 00:09:02,520 There are five dams on this stretch of river. 148 00:09:03,440 --> 00:09:06,640 This entire waterway, this system, 149 00:09:06,720 --> 00:09:09,640 has been created by these beavers. 150 00:09:09,720 --> 00:09:14,280 They've made these series of dams 151 00:09:14,360 --> 00:09:16,720 which kind of create this lock system. 152 00:09:18,480 --> 00:09:21,120 The beavers have turned what was a small stream 153 00:09:21,200 --> 00:09:23,480 into a series of deep ponds. 154 00:09:25,160 --> 00:09:28,200 These pools allow them to stay in the water while foraging. 155 00:09:29,840 --> 00:09:34,360 On land, they're easy prey for predators like wolves and bears, 156 00:09:35,760 --> 00:09:39,960 but crucially, this dam system also slows down the flood water. 157 00:09:42,680 --> 00:09:48,160 At two metres wide and 40 metres long, the main dam is the strongest. 158 00:09:48,240 --> 00:09:51,680 But if this one breaches, the others will go too. 159 00:09:53,400 --> 00:09:54,960 [YELPING] 160 00:09:57,400 --> 00:10:00,440 Right now, the beavers are safe in their lodge, 161 00:10:01,440 --> 00:10:04,600 but I'll follow them closely and find out how they get on 162 00:10:04,680 --> 00:10:06,240 as spring takes hold. 163 00:10:11,240 --> 00:10:12,360 HUMBLE: For many animals, 164 00:10:12,920 --> 00:10:16,320 spring is the most important time of year. 165 00:10:17,360 --> 00:10:18,880 It's now May. 166 00:10:19,280 --> 00:10:20,720 [SINGING] 167 00:10:21,600 --> 00:10:25,400 As soon as the snow melts, fresh vegetation appears. 168 00:10:25,600 --> 00:10:27,120 [STREAM GUSHING] 169 00:10:29,120 --> 00:10:32,080 Scientists call it the "spring green-up," 170 00:10:32,160 --> 00:10:35,400 and it drives all life in Yellowstone. 171 00:10:36,360 --> 00:10:40,040 One animal relies on it more than almost any other, 172 00:10:41,280 --> 00:10:43,320 the Rocky Mountain elk. 173 00:10:44,360 --> 00:10:47,560 There are over 20,000 elk in Yellowstone. 174 00:10:49,120 --> 00:10:53,680 As the green-up moves from the lowlands to high mountain pastures, 175 00:10:53,760 --> 00:10:55,320 the elk move with it. 176 00:10:56,640 --> 00:10:59,760 This magnificent herd of elk 177 00:10:59,840 --> 00:11:02,240 that is straddling right across the sagebrush here 178 00:11:02,320 --> 00:11:03,880 and up the hill, 179 00:11:03,960 --> 00:11:07,880 are on their way to the calving grounds a little bit further north from here. 180 00:11:07,960 --> 00:11:10,360 They'll be giving birth over the next few weeks. 181 00:11:11,000 --> 00:11:14,120 They'll hide their youngsters in the undergrowth, 182 00:11:14,200 --> 00:11:15,800 while they go off to feed. 183 00:11:17,400 --> 00:11:19,160 This is a crucial move 184 00:11:19,240 --> 00:11:23,680 in order to protect them from predation by the largest carnivore here, 185 00:11:24,280 --> 00:11:25,720 the grizzly bear. 186 00:11:26,440 --> 00:11:27,960 Now, there are some grizzlies 187 00:11:28,040 --> 00:11:33,280 that have become particularly adept at finding those youngsters, 188 00:11:33,360 --> 00:11:35,920 and that source of protein 189 00:11:36,000 --> 00:11:39,280 is really great for adult bears and their cubs 190 00:11:39,360 --> 00:11:43,440 needing desperately to put on weight after a long winter hibernation. 191 00:11:46,840 --> 00:11:50,400 It's as the snowline retreats from the valleys to the foothills, 192 00:11:50,480 --> 00:11:54,280 that the female grizzlies and their cubs start emerging. 193 00:12:00,040 --> 00:12:03,920 They usually stay close to their dens until the end of May, 194 00:12:04,000 --> 00:12:07,760 but this year, the warm weather has enticed the bears away 195 00:12:07,840 --> 00:12:09,280 earlier than usual. 196 00:12:12,480 --> 00:12:15,920 But the elk calves won't be born for another month. 197 00:12:17,080 --> 00:12:20,800 So life for these cubs will now be harder. 198 00:12:20,880 --> 00:12:25,160 They will have to scratch a living digging up roots and grasses. 199 00:12:30,560 --> 00:12:32,800 Grizzly expert Casey Anderson, 200 00:12:32,880 --> 00:12:36,880 is already seeing signs that there are plenty of bears around. 201 00:12:38,400 --> 00:12:41,640 They've been using trees as scratching posts. 202 00:12:42,760 --> 00:12:44,600 ANDERSON: Yeah, this thing's been getting hammered. 203 00:12:44,720 --> 00:12:47,000 Look at all this. They're leaving their scent behind, 204 00:12:47,880 --> 00:12:51,080 'cause there's just all kinds of mud and hair stuck on here, so... 205 00:12:51,680 --> 00:12:54,840 Yeah, it's going to be cool to see who is back in town. 206 00:12:56,280 --> 00:12:59,880 HUMBLE: Patrick is joining Casey in the Gallatin Mountains 207 00:12:59,960 --> 00:13:03,800 to find out whether the early bears are getting enough to eat. 208 00:13:06,480 --> 00:13:09,360 ARYEE: Casey's tracked a mother and her two-year-old cubs 209 00:13:09,480 --> 00:13:12,160 to a wooded area halfway down the mountain. 210 00:13:12,840 --> 00:13:17,640 They've been feeding all morning and are likely to be somewhere close by. 211 00:13:18,400 --> 00:13:22,040 [SOFTLY] From here on, we gotta go slow, even lower our voice. 212 00:13:23,040 --> 00:13:24,480 The wind's really goin' in the wrong direction. 213 00:13:25,440 --> 00:13:29,200 Wind's carryin' our scent right towards where the grizzly bears are 214 00:13:29,280 --> 00:13:31,360 and they have a sense of smell that's about seven times stronger 215 00:13:31,440 --> 00:13:33,160 -than a bloodhound. -All right. 216 00:13:33,240 --> 00:13:36,160 ARYEE: Casey thinks the bears will stay in this area for a while 217 00:13:36,240 --> 00:13:39,040 to make the most of the early green shoots. 218 00:13:39,120 --> 00:13:41,760 So for us, it's a waiting game. 219 00:13:43,760 --> 00:13:45,640 ANDERSON: It's amazing 'cause they just come out of nowhere. 220 00:13:45,720 --> 00:13:47,960 In that deep sagebrush, they love to just get down 221 00:13:48,040 --> 00:13:49,440 out of this wind 222 00:13:49,520 --> 00:13:51,440 and lay there flat to the ground, 223 00:13:51,520 --> 00:13:52,800 cuddle up, keep each other warm. 224 00:13:53,440 --> 00:13:55,560 So we just gotta keep scanning. 225 00:13:55,640 --> 00:14:00,080 You'll see, like, a little ear, or they'll stretch their little paw up. 226 00:14:00,200 --> 00:14:02,440 You gotta look for those little subtle things popping out. 227 00:14:04,360 --> 00:14:07,360 ARYEE: What makes you think that this is a good spot for bears? 228 00:14:07,720 --> 00:14:11,400 You look right down here in this green patch, 229 00:14:11,560 --> 00:14:15,800 you'll see where the bears have been excavating there, 230 00:14:15,880 --> 00:14:17,600 and that's just classic in the spring time. 231 00:14:17,680 --> 00:14:20,880 They'll find these, first, really green spots, 232 00:14:20,960 --> 00:14:23,040 that get a lot of moisture, get a lot of sun. 233 00:14:23,120 --> 00:14:27,280 So there's been a lot of activity down in that meadow there, so, 234 00:14:27,360 --> 00:14:29,120 it's a really good chance 235 00:14:29,200 --> 00:14:31,200 that whoever did that, whatever bears did that, 236 00:14:31,280 --> 00:14:33,640 are gonna come back to that spot and do it again. 237 00:14:36,040 --> 00:14:39,240 ARYEE: But plants contain less than half the protein of meat, 238 00:14:41,080 --> 00:14:44,680 so they'll have to eat huge amounts to keep up their calorie count. 239 00:14:53,320 --> 00:14:54,640 [WHISTLES AND WHISPERS] Right there! Right there! 240 00:14:54,880 --> 00:14:55,880 Where? 241 00:14:59,840 --> 00:15:00,960 Right here, right here. 242 00:15:01,040 --> 00:15:02,320 Right down in the trees. 243 00:15:04,160 --> 00:15:05,920 ARYEE: Oh, yeah, yeah, yeah, yeah, yeah, yeah. 244 00:15:06,360 --> 00:15:07,600 Three bears! 245 00:15:07,720 --> 00:15:09,200 [EXCITED LAUGH] 246 00:15:10,160 --> 00:15:11,240 ARYEE: One, 247 00:15:11,720 --> 00:15:13,000 two, 248 00:15:14,040 --> 00:15:15,640 three, looks like... 249 00:15:15,720 --> 00:15:20,200 Looks like a big female, one light cub, one dark cub. 250 00:15:21,520 --> 00:15:23,600 -It's pretty awesome! -Yeah. 251 00:15:26,240 --> 00:15:28,680 ANDERSON: Those look like two-year-old cubs. 252 00:15:29,360 --> 00:15:31,960 You know, this area is... Just draws in females with cubs. 253 00:15:32,640 --> 00:15:36,360 At a spot like that, well, you know, you get dandelions, grasses and sedge, 254 00:15:36,440 --> 00:15:38,760 even biscuit root will grow in that area, 255 00:15:38,840 --> 00:15:43,040 and that's all on the menu for a grizzly bear this time of year, so, 256 00:15:43,120 --> 00:15:44,880 they come right to that spot and they'll keep coming back 257 00:15:44,960 --> 00:15:47,240 over and over and over again, till everything is gone. 258 00:15:47,320 --> 00:15:51,960 So basically, this area here is kind of like an all-you-can-eat veggie buffet. 259 00:15:52,040 --> 00:15:53,520 Yeah, it's a salad bar. 260 00:15:55,040 --> 00:15:58,840 ARYEE: A dandelion plant contains only about three calories, 261 00:15:58,920 --> 00:16:00,960 and grass, even less. 262 00:16:02,080 --> 00:16:05,000 The early thaw is at least helping. 263 00:16:05,080 --> 00:16:10,080 But they must find two fields every day with rich sources of food like this one 264 00:16:10,160 --> 00:16:12,360 if they're going to survive. 265 00:16:20,360 --> 00:16:22,000 HUMBLE: It's not just grizzly bears 266 00:16:22,080 --> 00:16:24,840 that must exploit the best pockets of food. 267 00:16:27,560 --> 00:16:30,440 The Rocky Mountain elk are still moving north, 268 00:16:30,520 --> 00:16:32,040 following the green-up. 269 00:16:36,480 --> 00:16:39,680 And another of Yellowstone's residents is ahead of them, 270 00:16:40,360 --> 00:16:41,600 the bison. 271 00:16:42,480 --> 00:16:45,920 This year, the bison and elk are lucky. 272 00:16:46,000 --> 00:16:48,680 Not only have they had a milder winter, 273 00:16:48,760 --> 00:16:52,400 but the early thaw means there's plenty of grass around, 274 00:16:54,920 --> 00:16:58,120 and now in spring, it's full of protein. 275 00:17:02,040 --> 00:17:05,040 I've come to the northern range of Yellowstone. 276 00:17:06,120 --> 00:17:09,840 Park biologists have reported that a large herd of bison 277 00:17:09,920 --> 00:17:11,480 has come here to feast, 278 00:17:11,560 --> 00:17:14,640 because this year, the snow has already melted. 279 00:17:15,920 --> 00:17:18,760 The park is home to about 5,000 bison. 280 00:17:19,880 --> 00:17:20,920 [GRUNTING] 281 00:17:21,000 --> 00:17:24,840 This herd has made it through to spring fit and strong, 282 00:17:24,920 --> 00:17:28,840 which is crucial for the survival of their new-born calves. 283 00:17:30,240 --> 00:17:35,440 Calving season is just beginning here in Yellowstone National Park. 284 00:17:35,520 --> 00:17:39,200 This is the very first one I've seen. It's suckling I think. 285 00:17:41,400 --> 00:17:44,400 A quarter of the baby bison in Yellowstone 286 00:17:44,480 --> 00:17:47,280 die in their first two months, 287 00:17:47,360 --> 00:17:51,720 but this mild weather will give them a much greater chance of survival. 288 00:17:52,560 --> 00:17:54,040 There's a tiny one, 289 00:17:54,640 --> 00:17:57,320 looks like it's probably only a day or two old. 290 00:17:58,680 --> 00:18:02,160 Beautiful, you can see that lovely chestnutty colour. 291 00:18:02,680 --> 00:18:04,440 They're extraordinary, bison calves. 292 00:18:04,520 --> 00:18:07,600 Within half an hour of being born, they're up on their feet 293 00:18:07,680 --> 00:18:09,280 and within an hour or two, 294 00:18:09,360 --> 00:18:11,680 they can run to keep up with their mothers. 295 00:18:16,640 --> 00:18:19,520 Sticking close to their mothers is vital, 296 00:18:24,680 --> 00:18:25,880 because this spring, 297 00:18:25,960 --> 00:18:29,600 Yellowstone's top predator is particularly hungry. 298 00:18:29,680 --> 00:18:30,840 [WOLF HOWLING] 299 00:18:31,480 --> 00:18:35,000 There are 100 wolves in Yellowstone National Park. 300 00:18:36,680 --> 00:18:40,560 They rely on bison and elk to survive the winter. 301 00:18:42,840 --> 00:18:45,880 But whilst the mild winter has been good for the bison, 302 00:18:45,960 --> 00:18:47,880 it's been bad for the wolves. 303 00:18:48,280 --> 00:18:50,040 They've struggled to hunt. 304 00:18:52,280 --> 00:18:57,600 Back in the winter, biologist Doug Smith observed the problem first-hand. 305 00:18:58,400 --> 00:19:02,440 Doug and his team monitor these wolves every single day. 306 00:19:03,480 --> 00:19:07,200 They've noted that whilst mild winters help the prey, 307 00:19:07,280 --> 00:19:10,080 they put predators at a disadvantage. 308 00:19:11,600 --> 00:19:15,560 When you're in ankle-deep snow or just elbow-deep snow, 309 00:19:15,640 --> 00:19:20,560 a healthy elk, bison, deer will always outrun a healthy wolf. 310 00:19:21,360 --> 00:19:24,400 HUMBLE: Wolves and elk run at the same speed, 311 00:19:24,880 --> 00:19:27,160 but elk are built for endurance. 312 00:19:27,240 --> 00:19:30,720 With sure footing, they can keep going for longer. 313 00:19:31,160 --> 00:19:34,880 So this winter, the wolves have been going hungry. 314 00:19:37,560 --> 00:19:41,440 They're having a particularly tough time here in the northern range, 315 00:19:41,520 --> 00:19:45,360 where five packs compete for food and territory. 316 00:19:48,200 --> 00:19:51,440 Doug has studied these wolves for over 20 years 317 00:19:51,680 --> 00:19:55,640 and in the last decade, their numbers have fallen dramatically. 318 00:19:58,600 --> 00:20:03,400 One pack known by park biologists as the Lamar Canyon Pack 319 00:20:03,480 --> 00:20:05,320 is extremely weak. 320 00:20:06,120 --> 00:20:08,200 If they don't gain strength quickly, 321 00:20:08,320 --> 00:20:11,640 they risk losing their territory to other wolves. 322 00:20:13,920 --> 00:20:18,160 Our wildlife camera team is down in the Lamar valley, following them. 323 00:20:21,920 --> 00:20:25,440 From a mile off, they spot some unusual behaviour. 324 00:20:28,720 --> 00:20:32,320 The wolves are taking on a whole herd of bison. 325 00:20:34,920 --> 00:20:37,720 They're hoping to snatch a new-born calf. 326 00:20:38,720 --> 00:20:41,640 This is a sign that the pack is desperate. 327 00:20:44,160 --> 00:20:47,320 Doug is helping us to analyse what's going on. 328 00:20:49,880 --> 00:20:53,760 SMITH: These bison are doing classic defence. 329 00:20:54,920 --> 00:20:56,120 They group together, they're big. 330 00:20:56,200 --> 00:20:59,320 They're not moving other than to attack the wolves. 331 00:21:01,680 --> 00:21:06,400 HUMBLE: This is an age-old dance between power and agility. 332 00:21:07,640 --> 00:21:11,520 Wolves may be quick, but bison are strong. 333 00:21:13,080 --> 00:21:16,920 Getting this close risks a kick to the skull. 334 00:21:20,320 --> 00:21:24,520 SMITH: Wolves would like to spread this group apart, break it up 335 00:21:24,600 --> 00:21:26,440 and then that would free up one of these calves 336 00:21:26,520 --> 00:21:27,960 who they can grab. 337 00:21:32,920 --> 00:21:34,760 HUMBLE: A female charges, 338 00:21:34,840 --> 00:21:37,520 threatening to lash them with her hooves. 339 00:21:37,600 --> 00:21:40,800 SMITH: You get caught by a foot, you get caught by a horn, 340 00:21:40,880 --> 00:21:42,480 injury, death. 341 00:21:48,240 --> 00:21:50,600 It's fascinating footage to watch. 342 00:21:50,720 --> 00:21:53,640 They're being aggressive, yet very careful. 343 00:21:54,400 --> 00:21:59,520 Wolves definitely feel safer pursuing a fleeing prey, 344 00:21:59,600 --> 00:22:04,080 'cause they can kinda come in from behind, grab and pull down. 345 00:22:04,160 --> 00:22:08,120 HUMBLE: To attack a standing herd means these wolves are desperate. 346 00:22:09,920 --> 00:22:12,920 SMITH: As they get hungry and it goes more days without food, 347 00:22:13,000 --> 00:22:14,720 they're gonna take more risks. 348 00:22:15,520 --> 00:22:17,400 HUMBLE: They finally close in. 349 00:22:17,480 --> 00:22:20,720 This is the break in the herd they've been hoping for. 350 00:22:28,360 --> 00:22:29,920 [BISON GRUNTING] 351 00:22:30,000 --> 00:22:31,320 [WOLVES YELPING] 352 00:22:33,840 --> 00:22:36,080 SMITH: The mother can't do all this by herself, 353 00:22:36,160 --> 00:22:37,560 the wolves outnumber her. 354 00:22:39,200 --> 00:22:40,240 They may get this calf. 355 00:22:40,320 --> 00:22:42,960 I can't believe this, you rarely see this. 356 00:22:43,040 --> 00:22:44,240 [BISON GRUNTING] 357 00:22:52,800 --> 00:22:55,960 HUMBLE: But the calf makes it back to the safety of the herd, 358 00:22:57,720 --> 00:23:00,440 leaving nine very hungry wolves. 359 00:23:02,800 --> 00:23:05,640 The Lamar Canyon pack has failed. 360 00:23:11,800 --> 00:23:15,880 Doug is concerned that these warmer winters and early springs, 361 00:23:15,960 --> 00:23:19,080 are part of a worrying trend. 362 00:23:19,160 --> 00:23:22,680 We can see climate change affecting the park now. 363 00:23:22,760 --> 00:23:26,520 Our wolf research has only been going a little over 20 years, 364 00:23:26,600 --> 00:23:31,000 but you talk to people who were in Yellowstone 40 or 50 years ago 365 00:23:31,080 --> 00:23:34,800 and winter severity is, is just not like it used to be, 366 00:23:34,880 --> 00:23:38,280 and this is a big factor in how this system works. 367 00:23:39,960 --> 00:23:41,720 This winter and last winter 368 00:23:41,800 --> 00:23:44,440 were two of our shortest winters we've had. 369 00:23:44,520 --> 00:23:47,840 This, in a way, in a big-picture way, favours the bison. 370 00:23:47,920 --> 00:23:51,480 So we lost our snow at low elevation very early this year, 371 00:23:51,600 --> 00:23:55,080 and so any time the snow goes away, it gives the bison better footing. 372 00:23:55,160 --> 00:23:57,480 They can deal with the wolves, and secondly, 373 00:23:57,560 --> 00:24:00,120 it exposes the vegetation to sunlight, 374 00:24:00,200 --> 00:24:02,760 the condition of bison will start to improve earlier, 375 00:24:02,880 --> 00:24:04,960 uh, and so that hurts the wolves a little bit. 376 00:24:07,840 --> 00:24:09,760 And so, sitting aside and watching life evolve 377 00:24:09,840 --> 00:24:11,560 with that going on 378 00:24:11,640 --> 00:24:13,440 uh, has got me scared stiff. 379 00:24:15,960 --> 00:24:17,920 HUMBLE: It's the rate of climate change 380 00:24:18,000 --> 00:24:21,120 that Doug and his fellow scientists find so shocking. 381 00:24:22,280 --> 00:24:24,680 Temperatures here have been rising fast, 382 00:24:26,440 --> 00:24:30,520 and the last decade has been the warmest since records began. 383 00:24:34,480 --> 00:24:37,080 With Yellowstone's winters becoming shorter, 384 00:24:37,160 --> 00:24:39,600 and the spring starting earlier, 385 00:24:39,680 --> 00:24:43,160 one animal in particular is extremely vulnerable, 386 00:24:49,880 --> 00:24:51,560 the great grey owl. 387 00:24:55,720 --> 00:25:00,040 These owls live in some of the coldest forests on Earth, 388 00:25:00,120 --> 00:25:02,560 from Siberia to Scandinavia. 389 00:25:02,640 --> 00:25:07,120 Yellowstone is just about cold enough for the owls to survive. 390 00:25:07,200 --> 00:25:09,000 But if it gets any warmer, 391 00:25:09,080 --> 00:25:12,440 scientists believe they won't be able to hold on. 392 00:25:13,840 --> 00:25:18,320 Back in winter, cameraman Jeff Hogan followed a pair of great grey owls 393 00:25:18,400 --> 00:25:20,160 in the Teton Mountains. 394 00:25:26,880 --> 00:25:31,160 Great grey owls rely on small rodents like voles and gophers 395 00:25:31,240 --> 00:25:33,680 which live beneath the snow. 396 00:25:33,760 --> 00:25:37,080 But our biologists believe that the changing climate 397 00:25:37,160 --> 00:25:38,840 is affecting their hunting. 398 00:25:39,280 --> 00:25:42,800 These owls have to bust through this crust 399 00:25:42,880 --> 00:25:46,000 and then maybe another foot of snow to get at their prey. 400 00:25:47,840 --> 00:25:51,120 HUMBLE: But erratic winter weather caused the crust to melt, 401 00:25:51,200 --> 00:25:52,440 and then refreeze, 402 00:25:52,520 --> 00:25:55,520 making it impenetrable for the owls. 403 00:26:00,280 --> 00:26:05,480 And if they can't hunt, great grey owls won't nest or lay eggs. 404 00:26:10,680 --> 00:26:11,960 ARYEE: Now it's spring, 405 00:26:12,040 --> 00:26:15,960 Jeff has been searching for owl chicks in the Beartooth Mountains. 406 00:26:16,040 --> 00:26:19,320 The forest here is 300 years old, 407 00:26:19,400 --> 00:26:22,520 an ideal habitat for great grey owls. 408 00:26:27,200 --> 00:26:28,720 -There they are, three of 'em. -Oh, wow! 409 00:26:30,080 --> 00:26:31,440 [OWL SHRIEKS] 410 00:26:34,960 --> 00:26:36,160 Oh, my goodness. 411 00:26:40,160 --> 00:26:42,200 The smaller one, she's been a runt. 412 00:26:42,440 --> 00:26:44,360 ARYEE: Despite the difficulties of winter, 413 00:26:44,440 --> 00:26:46,920 we found a nest with three chicks. 414 00:26:47,000 --> 00:26:48,920 This is extremely unusual. 415 00:26:50,160 --> 00:26:53,800 When food is scarce, the smallest chick can be eaten by its siblings, 416 00:26:53,880 --> 00:26:56,040 but this runt is still alive. 417 00:26:57,720 --> 00:26:59,560 How much of a success is it 418 00:26:59,640 --> 00:27:02,360 that we've got three great grey owl chicks here? 419 00:27:03,000 --> 00:27:05,680 In these parts here, this neck of the woods, 420 00:27:05,880 --> 00:27:09,960 it's about a 20% success rate for the third chick. 421 00:27:10,040 --> 00:27:11,840 So most, you know, 422 00:27:11,920 --> 00:27:15,800 four out of five, perish by this... By this time. 423 00:27:17,440 --> 00:27:19,280 So we've got some great parents here. 424 00:27:19,360 --> 00:27:22,520 Yeah. The reason is, our winters have been quite mild, 425 00:27:22,600 --> 00:27:25,520 so the rodents, the prey, has really benefited 426 00:27:25,600 --> 00:27:27,600 and their populations have really grown, 427 00:27:27,680 --> 00:27:29,560 which of course, then, benefits the owls. 428 00:27:29,960 --> 00:27:31,720 And that could be making the difference 429 00:27:31,800 --> 00:27:33,960 on whether or not the chick survives or not. 430 00:27:35,440 --> 00:27:39,520 ARYEE: The early thaw this year has turned the owls' fortunes around. 431 00:27:39,600 --> 00:27:42,840 The milder weather has led to a boom in rodent numbers. 432 00:27:46,360 --> 00:27:49,200 To reveal how this has been helping the owls, 433 00:27:49,280 --> 00:27:52,880 Jeff has been searching for their pellets. 434 00:27:54,840 --> 00:27:57,520 Yeah, I've got a pellet here I collected this morning 435 00:27:57,600 --> 00:27:59,280 and look, you'll see the size of this. 436 00:27:59,360 --> 00:28:01,760 -[ARYEE LAUGHING] -HOGAN: It's kinda disgusting. 437 00:28:02,280 --> 00:28:05,160 Okay, well, if I just break this apart 438 00:28:05,240 --> 00:28:07,600 why, you can see it is literally just... 439 00:28:09,640 --> 00:28:11,880 ...hair and bone. 440 00:28:12,240 --> 00:28:13,240 HOGAN: Yeah. 441 00:28:14,240 --> 00:28:17,280 [GASPS] Look at that! 442 00:28:18,000 --> 00:28:20,760 That is an entire skull. 443 00:28:21,240 --> 00:28:22,320 Look at that, you can even see the teeth. 444 00:28:22,400 --> 00:28:23,960 -HOGAN: Mmm-hmm. -[GASPS] Here we go! 445 00:28:24,040 --> 00:28:25,040 Look, look, look, look! 446 00:28:25,160 --> 00:28:27,160 -HOGAN: There you go. -Oh, that is brilliant. 447 00:28:27,240 --> 00:28:28,240 Yeah. 448 00:28:28,840 --> 00:28:30,680 ARYEE: A second skull, 449 00:28:30,760 --> 00:28:33,560 which means they would have had two meals in quick succession. 450 00:28:34,720 --> 00:28:37,560 So far, the owls are doing well, 451 00:28:37,640 --> 00:28:40,760 but spring in Yellowstone is unpredictable. 452 00:28:42,960 --> 00:28:46,680 After I leave, the weather takes a turn for the worse. 453 00:28:46,760 --> 00:28:48,560 A storm blows in. 454 00:28:48,640 --> 00:28:50,920 It could mean death for the chicks. 455 00:28:51,560 --> 00:28:54,840 This rain makes... Makes it a little more difficult for me 456 00:28:55,640 --> 00:28:57,120 to work in, 457 00:28:58,000 --> 00:29:01,640 but it makes it even more difficult for the adult owls to hunt, 458 00:29:02,240 --> 00:29:05,960 being that it's just so noisy and it masks any sounds 459 00:29:06,040 --> 00:29:07,440 that the rodents may be making. 460 00:29:07,960 --> 00:29:10,800 ARYEE: The runt is at the bottom of the pecking order. 461 00:29:11,040 --> 00:29:14,960 As soon as food becomes scarce, she'll be the first to lose out. 462 00:29:15,400 --> 00:29:19,080 If the weather doesn't change, the runt may starve. 463 00:29:19,760 --> 00:29:21,200 [THUNDER CRASHING] 464 00:29:30,280 --> 00:29:34,240 HUMBLE: May is always the wettest month of the year in Yellowstone, 465 00:29:34,320 --> 00:29:37,840 but this year, it's far wetter than average. 466 00:29:40,800 --> 00:29:43,800 The reason can be found in the Pacific. 467 00:29:43,880 --> 00:29:48,080 The warming ocean creates much more moisture in the air. 468 00:29:48,960 --> 00:29:52,560 This is channelled directly up to Yellowstone, 469 00:29:52,640 --> 00:29:54,400 and when it hits the wall of mountains, 470 00:29:54,480 --> 00:29:57,760 the fury of the monsoon is unleashed. 471 00:29:58,080 --> 00:29:59,560 [THUNDER CRASHING] 472 00:30:04,240 --> 00:30:09,520 We experienced the most violent storm that's been seen here for many years. 473 00:30:10,560 --> 00:30:13,360 Rain falling over three mountain ranges 474 00:30:13,480 --> 00:30:16,320 drains straight into the Yellowstone basin. 475 00:30:16,680 --> 00:30:20,360 Overnight, water levels rise by a foot. 476 00:30:23,040 --> 00:30:25,720 For two weeks, rain pours down 477 00:30:25,800 --> 00:30:29,280 and thunderstorms reverberate around the mountains. 478 00:30:30,560 --> 00:30:33,160 Then, at last, in early June, 479 00:30:35,520 --> 00:30:36,800 the weather breaks. 480 00:30:38,760 --> 00:30:41,720 But there's water everywhere. 481 00:30:42,640 --> 00:30:44,960 Melting snow, as well as rainwater, 482 00:30:45,400 --> 00:30:47,960 is now flowing into the river systems. 483 00:30:52,520 --> 00:30:55,560 Scientists have told me to come to Yellowstone Falls 484 00:30:55,680 --> 00:30:57,600 to see the full effect. 485 00:31:19,000 --> 00:31:20,280 Back in March, 486 00:31:20,360 --> 00:31:22,360 Yellowstone Falls was just a mere trickle 487 00:31:22,440 --> 00:31:26,640 and now, it's a dramatic torrent of tumbling water. 488 00:31:31,040 --> 00:31:33,320 Every year, the thaw is different, 489 00:31:33,440 --> 00:31:35,680 and it's the rivers that hold the clues 490 00:31:35,760 --> 00:31:39,120 to tell us how this year's thaw is progressing. 491 00:31:52,840 --> 00:31:56,160 Thousands of animals rely on this river to survive. 492 00:31:57,880 --> 00:32:01,360 Greater Yellowstone sits on the continental divide. 493 00:32:02,120 --> 00:32:05,080 This water flows west to the Pacific ocean 494 00:32:05,160 --> 00:32:07,520 and east to the Atlantic. 495 00:32:08,400 --> 00:32:10,960 Without this huge reservoir of water, 496 00:32:11,040 --> 00:32:12,920 agriculture and industry, 497 00:32:13,000 --> 00:32:16,920 as well as wildlife in the American west would die. 498 00:32:17,960 --> 00:32:22,320 So, understanding how much water is draining into the river systems 499 00:32:22,400 --> 00:32:23,600 is vital. 500 00:32:24,360 --> 00:32:28,400 Teams of scientists have monitored the stream flow in Yellowstone's rivers 501 00:32:28,480 --> 00:32:31,000 for the last 86 years. 502 00:32:31,080 --> 00:32:34,680 They've noticed that recently, the pattern of the spring run-off 503 00:32:34,760 --> 00:32:36,160 has been changing. 504 00:32:37,520 --> 00:32:40,000 CHERYL MILLER: This piece of equipment measures stream flow. 505 00:32:42,920 --> 00:32:44,480 HUMBLE: Hydrologist Cheryl Miller 506 00:32:44,560 --> 00:32:47,080 is keeping a close eye on the rising water 507 00:32:47,160 --> 00:32:48,880 in the Yellowstone River. 508 00:32:49,280 --> 00:32:54,400 The data she gathers will reveal how big the spring run-off will be. 509 00:32:55,760 --> 00:32:58,400 It's all done with this little orange boat 510 00:32:58,480 --> 00:33:02,640 that uses sonar to measure the depth and speed of the water. 511 00:33:02,720 --> 00:33:07,440 Combine those and you get the flow, and that's the key figure. 512 00:33:08,680 --> 00:33:11,480 The rain has already raised the water levels, 513 00:33:11,560 --> 00:33:15,760 but it's the thousands of tons of snow still in the mountains 514 00:33:15,880 --> 00:33:18,400 that will make the real difference. 515 00:33:19,080 --> 00:33:21,120 -Okay, I've got her. -MILLER: All right. 516 00:33:21,920 --> 00:33:25,720 So if you get a very sharp rise in temperature, 517 00:33:25,800 --> 00:33:29,320 if that snow pack melts very quickly and, you know, I've been in those... 518 00:33:29,400 --> 00:33:31,520 I've been in that snow pack, the snow was above my head. 519 00:33:32,000 --> 00:33:35,560 Presumably, if that does melt very quickly, 520 00:33:35,640 --> 00:33:40,040 the results downstream must be, potentially, quite dramatic, 521 00:33:40,120 --> 00:33:41,680 quite destructive. 522 00:33:41,880 --> 00:33:46,160 Indeed. High-energy floods can make great changes along a river. 523 00:33:46,240 --> 00:33:48,400 What's happening now is, that the days are warm, 524 00:33:48,480 --> 00:33:50,720 but then, more importantly, the nights are warmer 525 00:33:50,800 --> 00:33:53,480 and so, that snow pack never refreezes at night. 526 00:33:53,600 --> 00:33:55,640 It continues to slowly melt during the night 527 00:33:55,720 --> 00:33:58,240 and so that's what allows the snow melt and the run-off 528 00:33:58,320 --> 00:34:00,120 -to accelerate during this time of year. -Yeah. 529 00:34:01,680 --> 00:34:03,360 HUMBLE: Just looking at the river, 530 00:34:03,480 --> 00:34:05,880 does it appear that the flow is faster now 531 00:34:05,960 --> 00:34:08,320 than it was when you last collected data? 532 00:34:08,400 --> 00:34:11,400 It is. It's come up in the last three or four days that it's... 533 00:34:11,480 --> 00:34:14,400 It may not be a lot faster, but the volume is definitely bigger. 534 00:34:14,480 --> 00:34:16,880 There's more stream flow than there was just a few days ago. 535 00:34:20,160 --> 00:34:22,280 HUMBLE: Cheryl's data reveals, this year, 536 00:34:22,360 --> 00:34:24,760 the melting snow is coming off the mountains 537 00:34:24,840 --> 00:34:26,800 more quickly than usual. 538 00:34:29,560 --> 00:34:34,080 The faster it runs off, the less water is absorbed into the ground. 539 00:34:35,760 --> 00:34:40,320 These rapid spring melts are more likely to cause flash floods. 540 00:34:41,200 --> 00:34:44,960 Patrick's finding out how that's affecting the beavers. 541 00:34:51,680 --> 00:34:55,280 Here in the Snake River valley, all the melt water from the Tetons 542 00:34:55,360 --> 00:34:57,280 is running down the mountains 543 00:34:57,360 --> 00:35:00,440 and it's headed directly for our beaver dam. 544 00:35:02,000 --> 00:35:05,040 I'm meeting up with cameraman Charlie Hamilton James. 545 00:35:05,920 --> 00:35:07,200 -Hey, Charlie. -Hey, Patrick. 546 00:35:07,280 --> 00:35:08,400 ARYEE: How's it going, man? 547 00:35:08,480 --> 00:35:10,160 JAMES: Yeah, it's good. Lovely weather, isn't it? 548 00:35:10,440 --> 00:35:12,720 ARYEE: He's spent the last week watching the beavers 549 00:35:12,800 --> 00:35:14,800 struggle with the rising river. 550 00:35:18,960 --> 00:35:22,840 The water level is so much higher 551 00:35:22,920 --> 00:35:24,920 compared to last time I was here. 552 00:35:25,000 --> 00:35:27,360 Yeah, actually, really only in the last few days, 553 00:35:27,440 --> 00:35:28,640 there was a lot of rain. 554 00:35:28,720 --> 00:35:30,520 All that water has resulted in this. 555 00:35:30,960 --> 00:35:32,040 JAMES: Yeah, I mean, and what it's done 556 00:35:32,160 --> 00:35:34,520 -is actually starting to flood the dam. -Mmm. 557 00:35:35,280 --> 00:35:38,680 ARYEE: In some places, the dam has already breached. 558 00:35:39,960 --> 00:35:43,880 The beavers are working nonstop to make sure all the leaks are plugged. 559 00:35:47,360 --> 00:35:49,840 They built this dam five years ago 560 00:35:49,920 --> 00:35:51,960 and every year, they fortify it. 561 00:35:53,640 --> 00:35:54,680 This one's been strengthened 562 00:35:54,760 --> 00:35:57,600 with a particularly high number of stones. 563 00:35:59,960 --> 00:36:02,360 So what makes this spot prime habitat? 564 00:36:02,440 --> 00:36:05,400 Well, actually, weirdly, beavers have made this spot. 565 00:36:05,480 --> 00:36:07,440 This actually started life as a stream 566 00:36:07,600 --> 00:36:10,880 and it's the beavers that came along and stuck these dams in it 567 00:36:10,960 --> 00:36:15,400 and blocked its path and created these long, slow ponds, 568 00:36:15,480 --> 00:36:16,920 and when you create a pond, 569 00:36:17,040 --> 00:36:18,960 you create another pond, you create another... 570 00:36:19,040 --> 00:36:21,160 You create a wetland ecosystem. 571 00:36:21,240 --> 00:36:23,920 They're basically engineers, but they're also gardeners. 572 00:36:24,320 --> 00:36:25,440 -I like that. "Gardeners." -So they're creating 573 00:36:25,520 --> 00:36:28,000 this whole environment that suits them. 574 00:36:28,080 --> 00:36:30,440 But it's not just them that benefit from this, right? 575 00:36:30,520 --> 00:36:32,320 -You've got amphibians, other mammals. -Oh, absolutely. 576 00:36:32,400 --> 00:36:34,120 -Birds, that rely on this. -Yeah, I mean, 577 00:36:34,200 --> 00:36:37,200 just sitting here now, there's birds everywhere, 578 00:36:37,280 --> 00:36:38,360 there's swallows flying around, 579 00:36:38,480 --> 00:36:40,400 drinking and catching flies off the surface. 580 00:36:40,840 --> 00:36:43,320 There's kingfishers eating fish. There's lots of minnows here, 581 00:36:43,400 --> 00:36:45,240 lots of small fish, perfect for kingfishers. 582 00:36:45,640 --> 00:36:48,560 Otters come through here, ospreys, eagles. 583 00:36:48,720 --> 00:36:51,920 So, you know, they're ecosystem builders is what they are, beavers, 584 00:36:52,000 --> 00:36:54,240 and more so, really than any other animal. 585 00:36:57,280 --> 00:36:59,120 ARYEE: If the main dam is knocked out, 586 00:36:59,200 --> 00:37:01,800 it's not just the beavers that will lose their home. 587 00:37:04,880 --> 00:37:07,320 The top is just about holding, 588 00:37:07,400 --> 00:37:12,080 but Charlie and I are heading underwater to find out how solid the base is. 589 00:37:17,720 --> 00:37:19,320 [INDISTINCT CONVERSATION] 590 00:37:20,720 --> 00:37:24,040 JAMES: Just where my feet are now, it actually starts here. 591 00:37:24,120 --> 00:37:26,160 The foundations are being laid here. 592 00:37:26,240 --> 00:37:28,240 And so, you know, it's like ten-foot wide. 593 00:37:28,320 --> 00:37:31,080 You can't see it all, 'cause most of it is underwater. 594 00:37:31,760 --> 00:37:33,240 We got these dry suits on. 595 00:37:33,320 --> 00:37:36,640 Yeah, and really, in perfect, in the spirit of full immersion, 596 00:37:37,560 --> 00:37:39,760 we should go in and actually have a look. 597 00:37:39,840 --> 00:37:41,760 Is this where I find out I've got the dud suit? 598 00:37:41,840 --> 00:37:43,200 JAMES: Yeah. 599 00:37:44,880 --> 00:37:46,120 [ARYEE CHUCKLES] 600 00:37:46,200 --> 00:37:48,760 JAMES: Actually, this is so much better than I thought it would be. 601 00:37:48,840 --> 00:37:49,840 This is awesome. 602 00:37:50,160 --> 00:37:52,520 It's much clearer than I thought. You can really see it. 603 00:37:54,640 --> 00:37:56,720 ARYEE: It's only when you get underwater 604 00:37:56,800 --> 00:38:00,000 that you see the skill that's gone into building this dam. 605 00:38:03,240 --> 00:38:06,200 The beavers choose logs up to two metres long 606 00:38:07,800 --> 00:38:12,080 and place them at an angle of 30 degrees to hold back the water. 607 00:38:12,160 --> 00:38:14,760 This is precision engineering. 608 00:38:19,720 --> 00:38:20,920 JAMES: It's amazing, isn't it? 609 00:38:21,000 --> 00:38:22,960 It's so impressive. This is... 610 00:38:23,040 --> 00:38:25,120 You know, it's kind of a work of art. 611 00:38:27,880 --> 00:38:31,440 But the beaver's hard work may not be enough. 612 00:38:31,520 --> 00:38:36,200 If the river rises any further, the water could break through, 613 00:38:36,280 --> 00:38:39,560 and this watery world might just disappear. 614 00:38:41,560 --> 00:38:42,760 [JAMES GRUNTING] 615 00:38:42,840 --> 00:38:44,160 JAMES: It's getting cold, though, isn't it? 616 00:38:45,400 --> 00:38:46,720 [INDISTINCT CONVERSATION] 617 00:38:49,800 --> 00:38:54,680 HUMBLE: It's now mid-June, and temperatures reach 28 degrees, 618 00:38:57,880 --> 00:39:01,520 seven degrees above average for this time of year. 619 00:39:08,920 --> 00:39:12,480 The snow recedes halfway up the mountains, 620 00:39:12,560 --> 00:39:16,880 revealing the highest feeding grounds in Greater Yellowstone, 621 00:39:16,960 --> 00:39:19,520 and close behind are all the animals 622 00:39:19,600 --> 00:39:24,320 taking advantage of the final stage of this year's spring green-up. 623 00:39:31,800 --> 00:39:34,120 At two and half thousand metres, 624 00:39:34,240 --> 00:39:38,760 this vast wilderness provides food for thousands of animals. 625 00:39:40,960 --> 00:39:43,440 Elk that over-wintered down in the valleys, 626 00:39:43,520 --> 00:39:46,720 finally arrive back in these high pastures, 627 00:39:46,800 --> 00:39:48,600 where they'll raise their calves. 628 00:39:52,960 --> 00:39:55,200 These meadows are a feasting ground, 629 00:39:55,720 --> 00:39:58,040 full to the brim with wildlife... 630 00:39:58,520 --> 00:40:01,320 The hunters, as well as the hunted. 631 00:40:01,640 --> 00:40:03,000 [WOLF GROWLING] 632 00:40:09,840 --> 00:40:14,440 Opportunistic black bears take advantage of a low bird's nest 633 00:40:14,520 --> 00:40:16,680 and defenceless chicks. 634 00:40:16,760 --> 00:40:20,640 At this time of year, any food is fair game. 635 00:40:23,040 --> 00:40:26,720 ARYEE: The grizzly bears are also joining the feeding frenzy. 636 00:40:27,440 --> 00:40:29,320 I'm catching up with Casey, 637 00:40:29,400 --> 00:40:33,200 who's following the fortunes of one young bear family. 638 00:40:33,960 --> 00:40:37,280 These new-born cubs are only four months old. 639 00:40:38,600 --> 00:40:40,320 With nowhere to hide from predators, 640 00:40:40,400 --> 00:40:44,160 this meadow is a dangerous place for baby bears, 641 00:40:44,240 --> 00:40:46,360 but their mother has no choice. 642 00:40:48,680 --> 00:40:50,560 She's following the melting snow 643 00:40:50,640 --> 00:40:53,400 to make sure that she and her cubs 644 00:40:53,480 --> 00:40:56,240 get enough protein from the new growth. 645 00:40:58,880 --> 00:41:01,000 -[LAUGHS] -Aw, they're so cute. 646 00:41:01,560 --> 00:41:03,800 -[LAUGHS] -ARYEE: So small. 647 00:41:07,000 --> 00:41:08,200 So you know this bear? 648 00:41:08,280 --> 00:41:09,920 Yeah, you can count on her like clockwork. 649 00:41:10,760 --> 00:41:15,840 Everything that a little cub needs to learn to survive its lifetime, 650 00:41:15,920 --> 00:41:18,160 they're learning in these first few years with its mother. 651 00:41:18,280 --> 00:41:20,000 Like, where to go, what time of the year, 652 00:41:20,080 --> 00:41:22,640 how to dig the roots. They're learning all that right now. 653 00:41:22,800 --> 00:41:23,920 This one here, you know, 654 00:41:24,000 --> 00:41:26,040 the year after year that I've watched her, 655 00:41:26,120 --> 00:41:28,880 she usually keeps almost all of her cubs. She's a great mother. 656 00:41:29,480 --> 00:41:32,520 ARYEE: In the ten years that Casey's been following this female, 657 00:41:32,600 --> 00:41:36,840 he's also seen her teach her offspring a more gruesome skill. 658 00:41:38,040 --> 00:41:40,040 She's a known predator. 659 00:41:40,120 --> 00:41:43,080 During this time of year, she will actually go around 660 00:41:43,160 --> 00:41:45,200 looking for elk calves that were just born 661 00:41:45,280 --> 00:41:46,840 that are stashed out here in the sage brush, 662 00:41:46,920 --> 00:41:49,720 and these little cubs will be in tow, and they'll be watching, so, 663 00:41:49,800 --> 00:41:51,040 it's a very learned behaviour. 664 00:41:51,120 --> 00:41:54,720 And some bears right in the same area don't hunt elk calves at all 665 00:41:54,800 --> 00:41:55,880 'cause their mother didn't teach 'em. 666 00:41:55,960 --> 00:41:57,920 They didn't get the chance to learn this. 667 00:41:58,000 --> 00:42:01,280 These little guys are gonna learn that and I'll tell you, this time of year, 668 00:42:01,360 --> 00:42:04,160 that protein for these little bear cubs is essential, 669 00:42:04,240 --> 00:42:06,880 and that may just be the thing that gives them the advantage 670 00:42:06,960 --> 00:42:08,920 to be strong bears. 671 00:42:09,360 --> 00:42:12,120 ARYEE: But of all the survival skills they'll need to learn, 672 00:42:12,200 --> 00:42:15,360 the most important is how to spot danger. 673 00:42:17,480 --> 00:42:20,960 There we've got Mum in the middle of this sagebrush, 674 00:42:21,040 --> 00:42:23,720 and these little cubs bobbing their head up and down. 675 00:42:24,720 --> 00:42:28,600 Surely this is a dangerous time for them as well? 676 00:42:28,680 --> 00:42:33,520 How difficult is it, you know, to be a new-born grizzly bear cub? 677 00:42:34,120 --> 00:42:35,320 ANDERSON: Very difficult. 678 00:42:36,000 --> 00:42:39,040 Stats say about 50% of bear cubs in their first year, 679 00:42:39,120 --> 00:42:40,120 they don't make it. 680 00:42:41,040 --> 00:42:44,080 And there are so many things out there that are trying to kill them. 681 00:42:45,120 --> 00:42:46,520 A male grizzly's one of them. 682 00:42:46,600 --> 00:42:47,760 You know, a male grizzly 683 00:42:47,840 --> 00:42:50,520 knows that she won't mate as long as she has cubs. 684 00:42:50,600 --> 00:42:52,280 He comes in there and he can eliminate those cubs, 685 00:42:52,360 --> 00:42:54,560 then she will come into oestrous and she will mate. 686 00:42:54,800 --> 00:42:59,040 So, big male bears, big danger for these guys. 687 00:43:01,280 --> 00:43:04,600 ARYEE: Male grizzlies are known to roam this area, 688 00:43:04,680 --> 00:43:07,240 so their mother must stay on high alert. 689 00:43:09,760 --> 00:43:12,160 And what's that scar on her head? 690 00:43:12,240 --> 00:43:14,000 It looks like she got some sort of scar. 691 00:43:14,120 --> 00:43:15,560 ANDERSON: Yeah, it's new for her, 692 00:43:15,640 --> 00:43:18,960 so I'm assuming, now that she's got these little cubs, 693 00:43:19,040 --> 00:43:21,000 that scar's probably from protecting them 694 00:43:21,080 --> 00:43:22,840 against a big male. 695 00:43:22,920 --> 00:43:27,160 And when it comes to their defence, these females, they don't care. 696 00:43:27,240 --> 00:43:29,160 They're gonna go against the biggest male grizzly, 697 00:43:29,240 --> 00:43:32,000 and it looks like she probably protected her cubs, 698 00:43:32,080 --> 00:43:33,400 but came away with a pretty big scar. 699 00:43:36,240 --> 00:43:37,600 Oh, she's nursing right now. 700 00:43:38,240 --> 00:43:40,560 -She's laying all the way on her back. -Oh, yeah. 701 00:43:40,760 --> 00:43:41,920 ANDERSON: Yeah, they're gonna get in there, 702 00:43:42,000 --> 00:43:43,360 they're gonna relax. 703 00:43:43,440 --> 00:43:45,400 Nothing better for a little cub than that right there, 704 00:43:45,480 --> 00:43:48,000 but Mom, she still has to pay attention, 705 00:43:48,080 --> 00:43:49,760 and you can see, she'll just keep picking her head up 706 00:43:49,840 --> 00:43:51,680 and watching, looking for danger. 707 00:43:52,000 --> 00:43:53,320 There's a good chance that these two little dudes 708 00:43:53,400 --> 00:43:54,840 will grow up to be adult bears, 709 00:43:55,800 --> 00:43:59,000 and she's a rock star mom for sure. 710 00:44:00,120 --> 00:44:04,560 ARYEE: Bears spend the heat of the day bedded down in the shade of the forest. 711 00:44:04,640 --> 00:44:07,640 But before this mother takes her cubs back to the woods, 712 00:44:07,720 --> 00:44:10,160 she has one more trick to teach them. 713 00:44:10,240 --> 00:44:12,520 How to keep cool in the hot sun. 714 00:44:13,480 --> 00:44:14,840 ANDERSON: These little patches of snow 715 00:44:14,920 --> 00:44:17,320 that are left from the snow drifts from the winter 716 00:44:17,800 --> 00:44:20,840 are everything for these bears, 'cause really, they're AC units, 717 00:44:20,920 --> 00:44:22,200 'cause the hotter it gets, 718 00:44:22,280 --> 00:44:24,440 they really could seek out these snow fields 719 00:44:24,520 --> 00:44:26,680 just to go and lay their bellies on and cool down. 720 00:44:35,160 --> 00:44:36,160 [ANDERSON LAUGHS] 721 00:44:36,680 --> 00:44:38,520 That's the best thing, they're so playful, 722 00:44:38,600 --> 00:44:40,320 so full of energy and just... 723 00:44:41,080 --> 00:44:42,520 They'll roll around like that for hours. 724 00:44:46,280 --> 00:44:49,680 You know, they're using that snow like a Slip'N Slide, 725 00:44:49,760 --> 00:44:53,120 just like kids playing on toboggans and sleds. 726 00:44:53,960 --> 00:44:55,680 ANDERSON: They're startin' to learn how to use their claws 727 00:44:55,760 --> 00:44:57,640 and their paws and get their balance, 728 00:44:57,720 --> 00:45:00,200 and if you look around out here, I mean, this is pretty rugged terrain, 729 00:45:00,280 --> 00:45:03,120 so they better get their feet underneath them pretty quick. 730 00:45:03,920 --> 00:45:06,560 I really believe that they like to have fun, 731 00:45:06,760 --> 00:45:08,160 just like any kid. 732 00:45:09,880 --> 00:45:13,880 ARYEE: But these snowy playgrounds will soon disappear 733 00:45:13,960 --> 00:45:16,800 as temperatures are now climbing every day. 734 00:45:20,320 --> 00:45:23,880 HUMBLE: In late June, we hit 30 degrees. 735 00:45:24,880 --> 00:45:27,200 The snow pack is collapsing. 736 00:45:33,160 --> 00:45:36,800 The great Yellowstone thaw reaches its peak. 737 00:45:50,240 --> 00:45:54,240 Thousands of tons of melt water cascade through the canyons, 738 00:45:56,080 --> 00:45:58,960 bulldozing everything in their path 739 00:45:59,040 --> 00:46:01,440 and crashes on into the valleys. 740 00:46:07,080 --> 00:46:13,120 Over 250 cubic metres of water is passing through the river per second. 741 00:46:20,440 --> 00:46:24,720 This melt water is vital for the regeneration of the land. 742 00:46:30,120 --> 00:46:31,840 But it comes at a cost. 743 00:46:34,600 --> 00:46:36,160 Despite the floodwater, 744 00:46:36,240 --> 00:46:40,960 Yellowstone's residents have to continue their daily quest to find food. 745 00:46:41,680 --> 00:46:44,840 Biologists have just told us that a herd of bison 746 00:46:44,920 --> 00:46:49,400 is attempting a river crossing not far from Yellowstone Falls. 747 00:46:50,480 --> 00:46:51,640 [LOW BELLOW] 748 00:46:52,480 --> 00:46:56,760 Our camera team arrives to find a two-month-old bison calf 749 00:46:56,840 --> 00:46:58,360 already struggling. 750 00:47:09,240 --> 00:47:11,840 It's been swept away from its mother. 751 00:47:13,800 --> 00:47:15,120 [LOUD BELLOW] 752 00:47:17,080 --> 00:47:19,320 Without her body to shield it, 753 00:47:19,440 --> 00:47:23,160 the calf is pounded by the full force of the current. 754 00:47:23,360 --> 00:47:24,560 [LOUD BELLOW] 755 00:47:30,400 --> 00:47:33,440 The other females have their own young to protect. 756 00:47:33,520 --> 00:47:35,960 This one is on its own, 757 00:47:37,720 --> 00:47:39,680 and it's losing energy fast. 758 00:47:59,160 --> 00:48:04,440 But the exhausted calf makes it safely to the new pastures on the other side. 759 00:48:07,360 --> 00:48:09,080 This one is lucky. 760 00:48:13,840 --> 00:48:18,120 And further south, the Snake River is also running high. 761 00:48:18,200 --> 00:48:20,200 There's so much floodwater, 762 00:48:20,280 --> 00:48:23,360 that one of the beaver's dams has burst. 763 00:48:24,520 --> 00:48:26,000 JAMES: Yeah, this is off, isn't it? 764 00:48:26,080 --> 00:48:28,920 Look at that. I mean, it's just blown out, isn't it? 765 00:48:29,000 --> 00:48:30,280 ARYEE: Wow. 766 00:48:30,360 --> 00:48:32,160 Yeah, that is completely busted. 767 00:48:32,240 --> 00:48:33,720 -JAMES: Yeah. -No, that water is flow... 768 00:48:33,800 --> 00:48:35,440 And it's a lot faster as well. 769 00:48:35,520 --> 00:48:37,160 JAMES: But do you know what? You're not gonna stop this. 770 00:48:37,240 --> 00:48:39,160 You know, the river has got to come down here, hasn't it? 771 00:48:39,240 --> 00:48:40,760 So it's either going to bust through the dam, 772 00:48:40,840 --> 00:48:42,000 or it's going to go over the top of the dam, 773 00:48:42,080 --> 00:48:43,440 -or it's going to go 'round the dam. -Yeah. 774 00:48:43,520 --> 00:48:45,360 And this dam just obviously wasn't quite strong enough. 775 00:48:45,480 --> 00:48:46,520 It's just bust through it. 776 00:48:46,920 --> 00:48:50,200 And you know, when this dam busts, it's gonna take out the next dam. 777 00:48:50,320 --> 00:48:52,080 You know, it's kind of a domino effect. 778 00:48:52,880 --> 00:48:55,080 JAMES: Oh, yeah! I mean, that is strong. 779 00:48:55,160 --> 00:48:57,280 So there's no way this can, 780 00:48:57,400 --> 00:48:59,280 you know, a pile of sticks is gonna stop this. 781 00:49:00,120 --> 00:49:02,600 ARYEE: Are they even gonna bother to fix that bit? 782 00:49:02,680 --> 00:49:04,440 JAMES: No, I don't think they will, because... 783 00:49:04,520 --> 00:49:07,000 Well, actually, you know, it'd be impossible to fix it. 784 00:49:07,080 --> 00:49:08,240 -ARYEE: Yeah. -They're not gonna do it. 785 00:49:08,320 --> 00:49:11,800 I reckon they'll wait, you know, a month, maybe, or more 786 00:49:11,880 --> 00:49:15,440 till the water goes right back down to pre-flood level, 787 00:49:15,520 --> 00:49:17,240 then they'll build it back up. 788 00:49:17,320 --> 00:49:20,000 ARYEE: You know, it doesn't look like much when you look upstream, 789 00:49:20,320 --> 00:49:24,440 but right here, all this water is pushing up against my body 790 00:49:24,520 --> 00:49:25,800 and there's so much force, 791 00:49:25,880 --> 00:49:28,000 and that's what the dam is having to contend with, 792 00:49:28,080 --> 00:49:30,000 that's what it's trying to hold back. 793 00:49:31,120 --> 00:49:32,880 If this dam has bust, 794 00:49:34,480 --> 00:49:36,560 what's happened to the beavers? 795 00:49:53,280 --> 00:49:55,720 The beavers are busier than ever. 796 00:49:55,800 --> 00:49:58,560 The water is flowing right over the top of their dam, 797 00:49:59,320 --> 00:50:01,600 but at the moment, it's still holding. 798 00:50:02,920 --> 00:50:05,600 They won't be able to fix it until the water levels fall. 799 00:50:17,560 --> 00:50:19,080 Inside the lodge, 800 00:50:19,160 --> 00:50:21,840 all the old bedding is pushed into the water. 801 00:50:23,800 --> 00:50:25,480 They leave it to soak for a while, 802 00:50:26,400 --> 00:50:29,880 and when it's clean, they drag it back in, 803 00:50:29,960 --> 00:50:32,520 giving them fresh new bedding for the summer. 804 00:50:39,080 --> 00:50:41,920 With temperatures now reaching 30 degrees, 805 00:50:42,000 --> 00:50:44,280 the owl chicks are struggling. 806 00:50:45,200 --> 00:50:47,400 One has already left the nest. 807 00:50:48,560 --> 00:50:51,080 These are birds that thrive in colder temperatures, 808 00:50:52,160 --> 00:50:56,040 but their nest is now exposed to the full force of the sun. 809 00:50:59,080 --> 00:51:01,640 Great grey owls struggle to lose heat, 810 00:51:01,720 --> 00:51:04,680 so the remaining two chicks must leave the nest 811 00:51:04,760 --> 00:51:06,200 as quickly as they can. 812 00:51:06,480 --> 00:51:08,000 [PANTING] 813 00:51:09,920 --> 00:51:12,720 HOGAN: [WHISPERING] The second chick is getting up on the lip, 814 00:51:12,800 --> 00:51:14,640 on the highest point of the nest, 815 00:51:14,840 --> 00:51:17,160 and just flaps like crazy. 816 00:51:17,240 --> 00:51:18,720 He's looking over the edge, 817 00:51:18,840 --> 00:51:21,200 and this is what they do before they jump. 818 00:51:22,880 --> 00:51:25,280 ARYEE: But the chicks are vulnerable. 819 00:51:25,360 --> 00:51:27,760 Their wings aren't strong enough to fly. 820 00:51:28,440 --> 00:51:33,240 When they jump, they'll plummet ten metres to the forest floor. 821 00:51:34,480 --> 00:51:36,560 [WHISPERS] Oh, he's gonna go, he's gonna go! 822 00:51:36,640 --> 00:51:37,960 Jump, jump! 823 00:51:40,520 --> 00:51:42,120 Go, go, go, go. Oh! 824 00:51:42,760 --> 00:51:45,280 He's leaning way over the other edge! 825 00:51:45,680 --> 00:51:47,000 Could go any second! 826 00:51:50,440 --> 00:51:53,800 ARYEE: It's the riskiest moment of this owl's life. 827 00:52:00,520 --> 00:52:01,680 [RUSTLING] 828 00:52:02,160 --> 00:52:05,040 It's not the most graceful maiden flight, 829 00:52:05,120 --> 00:52:07,640 but it's success nonetheless. 830 00:52:07,720 --> 00:52:09,920 HOGAN: [WHISPERING] He's hanging upside down! 831 00:52:10,440 --> 00:52:11,760 Got it all messed up. 832 00:52:12,360 --> 00:52:14,040 Oh, he is struggling. 833 00:52:15,160 --> 00:52:17,640 It's hanging by one talon. 834 00:52:19,320 --> 00:52:20,920 There he goes! 835 00:52:25,040 --> 00:52:28,160 It's one thing to launch, it's another thing to land. 836 00:52:30,880 --> 00:52:32,440 ARYEE: The chick lands safely, 837 00:52:33,440 --> 00:52:35,720 but it must head straight back up into the tree tops, 838 00:52:36,440 --> 00:52:38,640 away from predators on the forest floor. 839 00:52:42,120 --> 00:52:44,960 With Yellowstone's climate getting warmer each year, 840 00:52:45,040 --> 00:52:48,680 these owls may not be able to live here for much longer. 841 00:52:54,000 --> 00:52:57,200 Summer temperatures are becoming too hot. 842 00:53:02,840 --> 00:53:04,760 She's doesn't know what to do, where to go. 843 00:53:06,440 --> 00:53:08,480 ARYEE: The runt is now in danger. 844 00:53:10,400 --> 00:53:13,920 She's being struck directly by the intense heat of the sun. 845 00:53:16,160 --> 00:53:17,440 In these conditions, 846 00:53:17,520 --> 00:53:20,560 great grey owls struggle to regulate their body temperature. 847 00:53:20,720 --> 00:53:22,720 [PANTING] 848 00:53:29,920 --> 00:53:32,480 Panting helps her to cool down, 849 00:53:33,400 --> 00:53:37,000 but her downy feathers, which are so efficient in cold weather, 850 00:53:37,360 --> 00:53:38,760 may prove fatal. 851 00:53:39,320 --> 00:53:40,720 [PANTING FASTER] 852 00:53:43,880 --> 00:53:44,880 [CHIRPS] 853 00:53:45,880 --> 00:53:48,160 [SIGHS] That little girl's up again... 854 00:53:48,720 --> 00:53:50,400 Finally, but, 855 00:53:51,440 --> 00:53:55,600 she's hot too. She wants out of that heat, I can tell. 856 00:53:55,960 --> 00:53:59,960 ARYEE: This is a leap of faith she has got to make. 857 00:54:04,840 --> 00:54:08,200 She's back on the launch pad. This is where I think she's gonna go. 858 00:54:12,040 --> 00:54:13,160 She's... 859 00:54:25,560 --> 00:54:26,880 She launched! 860 00:54:26,960 --> 00:54:28,200 She launched! 861 00:54:30,040 --> 00:54:31,040 [CHIRPS] 862 00:54:34,800 --> 00:54:40,560 HOGAN: So this forest is now home to three more great grey owls. 863 00:54:41,040 --> 00:54:42,400 I'm impressed. 864 00:54:42,600 --> 00:54:44,200 I'm proud of this little girl. 865 00:54:45,240 --> 00:54:48,200 You know, maybe one day she's gonna just come back here 866 00:54:48,280 --> 00:54:51,840 and raise a great grey owl family of her own. 867 00:55:06,320 --> 00:55:09,200 HUMBLE: As the longest day of the year approaches, 868 00:55:09,280 --> 00:55:11,320 spring becomes summer. 869 00:55:12,360 --> 00:55:13,640 The animals we've followed 870 00:55:13,720 --> 00:55:17,200 have made it through Yellowstone's most challenging season. 871 00:55:18,720 --> 00:55:23,040 This year, the thaw started three weeks earlier than usual... 872 00:55:26,160 --> 00:55:30,680 An area of 30,000 square miles has been transformed... 873 00:55:34,560 --> 00:55:38,280 And the mountains have released over a millions tons of water. 874 00:55:40,440 --> 00:55:43,720 And finally, from top to bottom, 875 00:55:43,800 --> 00:55:46,360 Yellowstone is free of snow. 876 00:55:47,160 --> 00:55:50,560 Now our animal families face the new challenge of summer, 877 00:55:50,640 --> 00:55:53,520 when temperature can soar and vegetation wither. 878 00:55:54,840 --> 00:55:57,160 And that leads to a new threat, 879 00:55:57,920 --> 00:55:59,400 wildfires.