:00:00. > :01:20.These sooty terns are amongst the most aerial of birds.
:01:21. > :01:40.But there is one thing that compels them to come down to earth.
:01:41. > :01:57.Flying with an egg inside the body, let alone a clutch of three or four
:01:58. > :02:01.makes huge demands on the energy of a bird.
:02:02. > :02:16.In places like this island in the Seychelles,
:02:17. > :02:44.so they are equally spaced with almost mathematical precision.
:02:45. > :02:56.The fairy tern, for some reason, always puts them on a bare branch
:02:57. > :03:03.though whether that is safer or more dangerous is debatable.
:03:04. > :03:15.The dimple left when a branch breaks away is not bad either.
:03:16. > :03:19.But it seems reckless to rely on a little dead twig like this
:03:20. > :03:24.particularly with the strong trade winds of the Seychelles.
:03:25. > :03:30.The fact is that unguarded fairy terns' eggs are easily dislodged.
:03:31. > :03:52.Skinks know that and so do the fodys, the local sparrows.
:03:53. > :03:57.And that has solved the problem of how to crack it.
:03:58. > :04:16.and birds may have to go to great lengths to keep them safe.
:04:17. > :04:30.Swifts, living on the mainland, have to take greater precautions.
:04:31. > :04:56.To make sure the egg stays in this flimsy hammock of feathers,
:04:57. > :05:09.they stick THAT to the leaf as well.
:05:10. > :05:15.Changing places to take over incubation is a tricky operation
:05:16. > :05:39.when your nest is stuck to a vertical surface.
:05:40. > :06:17.Swifts, once again, exploit their mastery of flight
:06:18. > :06:25.Great dusky swifts roost for the night
:06:26. > :06:28.on the mist-drenched rocks beside the Falls.
:06:29. > :06:33.But this is not a safe enough place for their precious eggs.
:06:34. > :06:38.They will be deposited actually BEHIND the curtain of water
:06:39. > :07:06.and to do that the birds must find the thinnest part of it.
:07:07. > :07:11.Behind the curtain, they still have an awkward climb
:07:12. > :07:30.before they reach a place where it is possible to put an egg.
:07:31. > :08:29.They're parrots and they are nesting on the coast of Argentina.
:08:30. > :08:40.is also an excellent excavating tool.
:08:41. > :08:45.These cliffs' relatively soft sandstone is no problem for a parrot.
:08:46. > :08:56.and there is a great deal of competition over any vacancy.
:08:57. > :09:09.Sand martins are not so well equipped for digging.
:09:10. > :09:16.and they can only tackle sandstone if it is soft and friable.
:09:17. > :09:33.But what they lack in equipment they make up for with energy.
:09:34. > :09:39.Woodpeckers being expert carpenters chisel their nestholes in trees,
:09:40. > :09:44.but this one is digging into softer material - an ants' nest.
:09:45. > :09:52.But they quickly get used to their lodger sitting in their mansion,
:09:53. > :09:57.and then they attack any intruder that tries to steal her eggs.
:09:58. > :10:03.You might think a hornbill has THE most powerful excavation tool.
:10:04. > :10:22.So hornbills have to find natural holes or ones dug by others.
:10:23. > :10:29.A pair do their house hunting together and they are very choosy.
:10:30. > :11:16.The male regurgitates a little food for her.
:11:17. > :11:20.Now she has decided that this is for her,
:11:21. > :11:31.She seals herself in, narrowing the entrance
:11:32. > :11:37.with a plaster made of chewed wood, mashed food and her own droppings.
:11:38. > :11:58.The majority of birds, though, don't nest in holes.
:11:59. > :12:41.but these frigates on the Galapagos have an added problem.
:12:42. > :12:45.Their short feet and wide wings make it difficult to land,
:12:46. > :12:51.so they much prefer to collect their building material on the wing.
:12:52. > :12:56.Boobies can settle and break off the branches they need for their nests.
:12:57. > :14:33.is the most difficult part of the whole business.
:14:34. > :14:43.Stolen goods, it's true, but all the more precious for that.
:14:44. > :14:49.Once they start to develop they have to be kept warm
:14:50. > :14:58.Ducks and geese line their nests with feathers from their breasts.
:14:59. > :15:02.Other birds are not so self-sacrificing
:15:03. > :15:06.and use those that they find blowing about.
:15:07. > :15:24.Tree swallows compete with one another in collecting them.
:15:25. > :15:49.and a rival won't give you a second chance.
:15:50. > :16:41.is all within the rules of this particular game.
:16:42. > :16:46.The golden-headed cisticola - a kind of Australian warbler -
:16:47. > :16:51.uses fibres and spiders' webs not just for lining but for stitching.
:16:52. > :17:35.There is no more skilled tailor in the whole of the bird world.
:17:36. > :17:39.There's little problem about concealing this nest
:17:40. > :17:43.for the leaves she stitches together remain alive and green.
:17:44. > :17:55.The problem is greater when a nest sits on the bare branches of a tree.
:17:56. > :18:01.The sitella - an Australian equivalent of the nuthatch -
:18:02. > :18:05.constructs its nest from spiders' webs and insect cocoons,
:18:06. > :18:09.and then covers the outside with rather coarser material.
:18:10. > :18:20.This one is in a tree covered in lichen.
:18:21. > :18:24.And this is in one that has flaky bark.
:18:25. > :18:30.The sitellas are not rigidly-minded birds with inflexible habits,
:18:31. > :18:34.they use lichen to cover the nest in the lichen tree.
:18:35. > :18:52.And bark on the one in the flaky bark tree.
:18:53. > :18:58.As a result each is as well camouflaged as anyone could hope
:18:59. > :19:02.and though both nests are plain for all to see,
:19:03. > :19:13.they're not easily recognised for what they are.
:19:14. > :19:34.A pair with their grown-up young from previous seasons work together.
:19:35. > :19:40.It used to be believed that there was always a dozen in the team
:19:41. > :19:43.which is why they were called apostle birds.
:19:44. > :19:50.And the team works so industriously and so harmoniously
:19:51. > :19:58.that their elegant cup is usually completed in a mere 3 days.
:19:59. > :20:04.A bird's beak it seems can serve just as well as a plasterer's trowel
:20:05. > :20:28.Some birds build nests not just as cradles for their eggs and chicks
:20:29. > :20:32.but as lodging houses for the whole year.
:20:33. > :20:49.This haystack may be more than a century old.
:20:50. > :20:55.It's so heavy that part of it has broken the branch that supported it.
:20:56. > :21:08.It's been built and maintained as a communal effort by its inhabitants.
:21:09. > :21:12.Weavers are closely related to sparrows.
:21:13. > :21:37.has a considerable advantage over small isolated nests
:21:38. > :21:44.During the day it gets ferociously hot,
:21:45. > :22:15.And then the thatch is probably at its most valuable.
:22:16. > :22:28.and the birds that roost inside remain snug and warm.
:22:29. > :22:33.Not all the chambers are for nesting.
:22:34. > :22:43.in which several of the colony snuggle together for warmth.
:22:44. > :22:51.simple or complex, is prepared for the egg
:22:52. > :22:54.and it is time for the female to produce one.
:22:55. > :22:57.The male frigate welcomes his partner back.
:22:58. > :23:47.Mated female birds have been feeding intensively
:23:48. > :24:26.Here it lingers for 24 hours while the shell is added.
:24:27. > :24:30.Pigment glands squirt little spots of colour on it.
:24:31. > :24:49.And so, an avocet produces her egg.
:24:50. > :25:03.These are the eggs of a golden plover.
:25:04. > :25:08.Laid on the ground they are practically invisible,
:25:09. > :25:29.as indeed the bird that laid them will be, once she settles down.
:25:30. > :25:37.A few birds, however, have adopted a rather more risky policy.
:25:38. > :25:45.If they do that they must lay it in a really secure nest,
:25:46. > :25:49.hidden, for example, deep in a burrow as the kiwi does.
:25:50. > :25:55.Her egg is gigantic, the biggest laid by any bird
:25:56. > :25:59.and a quarter of her total body weight.
:26:00. > :26:35.Expelling such an egg is obviously a huge effort.
:26:36. > :26:47.The owner of this nest, a blue tit, adopts a very different strategy.
:26:48. > :26:52.Her egg is tiny. It weighs no more than a gram.
:26:53. > :27:14.and the survival rate in the end will be not unlike the kiwi's.
:27:15. > :27:17.Few eggs are totally safe from hungry raiders
:27:18. > :27:22.no matter how skilfully protected and artfully concealed they are.
:27:23. > :27:56.But the red-breasted toucan has a long beak.
:27:57. > :28:04.This toucan's bill is just not long enough for these particular nests.
:28:05. > :28:22.But the toco toucan has an even longer one.
:28:23. > :29:24.they will have to build even longer nests in the future.
:29:25. > :29:30.In Australia the prime egg thief is the currawong.
:29:31. > :30:03.and the Australian birds have developed many strategies
:30:04. > :30:11.This is the nest of a yellow-rumped thornbill.
:30:12. > :30:19.You might think therefore that it has been robbed of its eggs.
:30:20. > :30:24.But in fact this part of the nest has never had any eggs in it.
:30:25. > :30:30.There's another entrance. It's down here.
:30:31. > :31:02.This wren in Costa Rica has another way of protecting its eggs.
:31:03. > :31:16.and equally obvious is another one close by - a wasps' nest.
:31:17. > :31:26.It is a brave thief that risks being attacked by these.
:31:27. > :31:39.But coatimundis ARE brave, sometimes to the point of recklessness.
:31:40. > :32:53.one of the adults immediately responds.
:32:54. > :32:57.Ahead, I can just see a bird crouching on her eggs.
:32:58. > :33:11.And now she starts a most bizarre pantomime.
:33:12. > :33:15.This hardly looks like any kind of bird
:33:16. > :33:30.and whatever it is, it seems to be crippled.
:33:31. > :33:43.an injured bird or maybe a little rodent.
:33:44. > :34:19.Having deflected me, she returns to her nest.
:34:20. > :35:01.In this one unshaded patch, the sand is kept so hot by the sun
:35:02. > :35:18.The birds have to be accurate judges of temperature.
:35:19. > :35:23.If they don't dig deep enough, their eggs will bake,
:35:24. > :35:44.Now all that's needed is to fill in the hole.
:35:45. > :35:56.These eggs, in Alaska, must be tended more assiduously.
:35:57. > :36:09.There is even a glimpse of pink naked skin.
:36:10. > :36:14.Her body has to be particularly well insulated with dense plumage
:36:15. > :36:19.to prevent it losing heat in these near-freezing conditions.
:36:20. > :36:26.Yet somehow she has to transfer some of that heat to these eggs.
:36:27. > :36:37.This naked brood patch on her belly will enable her to do just that.
:36:38. > :36:57.She cannot leave her eggs for more than a minute or two
:36:58. > :37:17.and he will have to do this for almost two months.
:37:18. > :37:52.The mated female has not yet built a nest of her own
:37:53. > :38:06.so she makes her way to the one who has.
:38:07. > :38:11.The sitting female clearly doesn't like this intrusion
:38:12. > :38:32.but equally she's not going to abandon her eggs.
:38:33. > :38:36.The intruder pushes her to one side and quickly lays.
:38:37. > :38:42.Sometimes the sitting bird doesn't seem to realise what has happened
:38:43. > :38:58.The male has a redder head and neck, the redhead duck.
:38:59. > :39:03.His female also has her eye on the canvasback's nest.
:39:04. > :40:13.The female canvasback leaves her nest for a meal
:40:14. > :40:17.and reveals that this last intrusion was not the first.
:40:18. > :40:22.There are three white redhead eggs in her nest.
:40:23. > :40:44.And there are plenty of hazards against which a duck needs to insure
:40:45. > :41:54.There really is sense in not putting all your eggs in one basket.
:41:55. > :41:59.Some birds, however, don't care for any of their eggs.
:42:00. > :42:09.This is the nest of an Australian fantail.
:42:10. > :42:20.It's so different that you would think the fantails would realise.
:42:21. > :42:31.but it's the male who comes back first.
:42:32. > :42:42.He seems quite unaware that anything is wrong.
:42:43. > :42:46.The female cuckoo is also keeping an eye on things.
:42:47. > :42:51.The fantail has accepted the egg, and that will be disastrous -
:42:52. > :42:56.when the bigger cuckoo chick hatches, it will push out the baby fantails.
:42:57. > :43:09.In North America, the cowbird is also playing this game.
:43:10. > :43:13.It has put an egg in the nest of a gnatcatcher.
:43:14. > :43:18.It's slightly bigger but very similarly marked.
:43:19. > :43:38.Will the gnatcatchers notice the difference?
:43:39. > :43:48.There is no future for their own chicks in this one.
:43:49. > :43:52.But nesting material is too valuable to waste.
:43:53. > :44:09.They begin a new nest quite close by.
:44:10. > :44:26.destroying the old and building the new.
:44:27. > :44:37.The cowbird has lost this particular duel.
:44:38. > :44:41.Africa. The duels are being fought out here too.
:44:42. > :44:45.This is a colony of lesser masked weavers
:44:46. > :45:09.And the weavers seem well aware of the danger.
:45:10. > :45:27.as they must have been doing for many centuries.
:45:28. > :46:15.But the cuckoo is having a lot of trouble getting in.
:46:16. > :46:21.Cuckoo eggs have been frequently found in the nests of these weavers.
:46:22. > :46:25.but none seem to be getting into this colony.
:46:26. > :46:45.The battle seems to be swinging the weavers' way.
:46:46. > :46:51.Nearby, there's a colony of a slightly different kind of weaver,
:46:52. > :46:59.They don't put entrance tubes to their nests
:47:00. > :47:04.perhaps because they themselves are nearer the size of a cuckoo
:47:05. > :47:09.so any entrance they can get into, a cuckoo could also.
:47:10. > :47:17.The colours of their eggs are extraordinarily variable.
:47:18. > :47:21.But any one cuckoo can only lay one kind of egg.
:47:22. > :47:27.And it has no way of knowing what colour the eggs are in any one nest.
:47:28. > :47:30.So the odds are against the eggs matching.
:47:31. > :47:34.Now I happen to know that this nest contains speckled eggs.
:47:35. > :47:45.What happens if I put a pale egg in it?
:47:46. > :48:02.No doubt about who's winning here either - this time.
:48:03. > :48:09.The battle between cuckoos and other birds is a continuing one,
:48:10. > :48:17.and the victims finding new defences.
:48:18. > :48:22.Soon, in those nests behind me, eggs will start hatching.
:48:23. > :48:27.Most will produce young weaver birds, but some, equally certainly,
:48:28. > :48:38.Whichever they are, the young chicks will have a whole set of problems
:48:39. > :48:42.they have to solve before growing into adults.
:48:43. > :49:22.is what we will be looking at in the next The Life of Birds.
:49:23. > :51:52.On the open moorland there is plenty of room for a nest and not enough
:51:53. > :51:59.food for lots of birds, so there is no problem of overcrowding and the
:52:00. > :52:04.rarity of a well camouflaged nest is good protection.
:52:05. > :52:08.If you have a chisel as efficient as a kingfisher's beak you can cut a
:52:09. > :52:19.very safe home for yourself in a tree.
:52:20. > :52:23.A hole like this made by the South African woodland kingfisher is not
:52:24. > :52:29.very conspicuous and easy to defend, since the sitting bird can use its
:52:30. > :52:33.beak not only as a chisel but as a spear.
:52:34. > :52:38.But for the Australian crested bell bird it seems that the essentials
:52:39. > :52:43.are not enough. A home should not only be secure, it should be
:52:44. > :52:50.decorated. The bird goes through a lot of
:52:51. > :52:56.trouble to garland the rim of its nest can caterpillars.
:52:57. > :53:02.The caterpillars don't crawl away. This is because the bell bird has
:53:03. > :53:06.given each of them a nip behind its head that has immobilised it but
:53:07. > :53:12.they are not just decoration. They are covered with hairs that have a
:53:13. > :53:19.particularly powerful sting, painful enough to deter a small mammal from
:53:20. > :53:26.sticking its sensitive nose into to the nest.
:53:27. > :53:28.For a happy and successful home, there is nothing more important than
:53:29. > :53:43.security. Bringing up baby always causes
:53:44. > :53:48.difficulties, and birds are no exception. This young tern is an
:53:49. > :53:53.insatiable creature demanding to be fed over and over givenry day, but
:53:54. > :53:58.different birds have different requirements and some face the most
:53:59. > :54:02.extraordinary dangers, as you can discover from the problems of
:54:03. > :55:14.parenthood, the next programme in the Life of Birds.
:55:15. > :55:17.'We wanna do a science fiction series.'