0:00:02 > 0:00:07*
0:00:37 > 0:00:43If you travel by air, it's very important to keep your weight down to a minimum.
0:00:47 > 0:00:51You can't afford to carry a lot of fuel around,
0:00:51 > 0:00:56and what you do carry should be energy-packed and not too bulky.
0:00:56 > 0:01:01And oak trees put just such a substance into their acorns.
0:01:01 > 0:01:08It's to fuel the growth of their seedlings, and they protect it with a hard shell.
0:01:08 > 0:01:10But jays know how to deal with that.
0:01:23 > 0:01:26A beak is a concession to weight-saving.
0:01:26 > 0:01:33It's much lighter than the jaws and teeth reptiles and mammals use to process food,
0:01:33 > 0:01:37yet it's also very efficient and versatile.
0:01:39 > 0:01:48A jay, using its beak like a pick, can cut through an acorn's armour without any difficulty.
0:01:48 > 0:01:50Beaks are closely matched to diet.
0:01:50 > 0:01:54A goldfinch uses its beak like a pair of tweezers.
0:01:54 > 0:02:00It's just the right length for extracting the seeds from between a teasel's spines.
0:02:06 > 0:02:12A blue tit has a stubbier beak. That gives it the strength to crack small seeds,
0:02:12 > 0:02:17but it also prevents its owner from getting them from a teasel.
0:02:17 > 0:02:22A greenfinch's beak is even stouter and stronger,
0:02:22 > 0:02:24but it's far from clumsy.
0:02:24 > 0:02:32Watch how, with help from its tongue, the bird delicately removes the outer shell from these rosehip seeds.
0:02:36 > 0:02:40The strongest beak in the finch family belongs to the hawfinch.
0:02:40 > 0:02:43It can even deal with a cherry stone,
0:02:43 > 0:02:47but the bird doesn't simply rely on brute force.
0:02:47 > 0:02:53First, it moves the cherry stone into just the right position for easy cracking.
0:02:53 > 0:02:56It gets rid of the broken shell...
0:02:59 > 0:03:07..and now it starts the fiddly operation of removing the papery husk that covers the kernel.
0:03:24 > 0:03:31Pine trees - these are in California - protect their seeds by enclosing them in cones.
0:03:31 > 0:03:36When they're green, the seeds within are beyond the reach of most birds.
0:03:36 > 0:03:41But the crossbill has special equipment.
0:03:43 > 0:03:51It's the only finch that can twist its upper and lower bill in opposite directions.
0:04:04 > 0:04:11Now, right at the bottom, it can feel the soft young seed with its tongue.
0:04:13 > 0:04:15Got it!
0:04:18 > 0:04:27After a meal of pine seeds, these American crossbills regularly fly off to a bank of exposed clay.
0:04:27 > 0:04:31They're in need of digestive tablets.
0:04:31 > 0:04:36Green pine cones are very resinous and may cause stomach upsets,
0:04:36 > 0:04:43but clay in the stomach will absorb the resin and so prevent any trouble.
0:04:43 > 0:04:48A crossed bill, however, is not the best implement for digging -
0:04:48 > 0:04:54you've to twist your head to one side to get your bill into the ground,
0:04:54 > 0:04:59but they get enough to allow them daily meals from pine trees.
0:05:05 > 0:05:11Seeds in the temperate parts of the world, whether pine cones, cherry stones or acorns,
0:05:11 > 0:05:16all have a major disadvantage as a food for birds -
0:05:16 > 0:05:19they're very seasonal.
0:05:19 > 0:05:24There's none in spring and summer and a glut in autumn.
0:05:24 > 0:05:30A single oak tree like this, in a season, can produce 90,000 acorns,
0:05:30 > 0:05:34but there are lots of things, apart from birds, that eat acorns.
0:05:36 > 0:05:38Squirrels do, for a start.
0:05:38 > 0:05:43If a jay is to collect acorns in autumn, it will have to be quick,
0:05:43 > 0:05:46before others grab them all.
0:05:59 > 0:06:04It's carrying one in its beak because its crop is full,
0:06:04 > 0:06:10as you can see from that bulge on its throat. There can be up to nine acorns in there.
0:06:15 > 0:06:22But what is a jay going to do with such quantities? It can't eat them all.
0:06:22 > 0:06:25They store them - by burial.
0:06:32 > 0:06:38One jay, in a month, may bury as many as 3,000 acorns.
0:06:38 > 0:06:45What is more, when winter comes and it needs food, it will remember exactly where most of them are.
0:06:51 > 0:06:55In North America, oaks still form huge forests
0:06:55 > 0:07:01and they produce acorns on an astronomical scale.
0:07:01 > 0:07:05Among those that harvest them are woodpeckers.
0:07:05 > 0:07:10A woodpecker's beak is a drill and a very efficient one, too,
0:07:10 > 0:07:14so it's not surprising that it stores acorns by drilling.
0:07:17 > 0:07:24There are as many as 60,000 acorns stored in the holes drilled in this one tree.
0:07:36 > 0:07:43All the members of this woodpecker family - eight birds in all - use this one tree.
0:07:53 > 0:08:01To start with, the birds deposit newly gathered acorns in a hole to allow them to dry off.
0:08:09 > 0:08:16Then, when they've shrunk as much as they're going to do immediately, they're given individual storage.
0:08:27 > 0:08:34This larder provides food for the family throughout the year, but the birds have to be vigilant
0:08:34 > 0:08:39and ready at all times to repel raiders.
0:08:44 > 0:08:49There's also a lot of maintenance work to be done.
0:08:49 > 0:08:55As the acorns continue to dry and to shrink, they become loose in their sockets.
0:08:55 > 0:09:02That would never do - they'd be easy for someone to steal, they might even drop out.
0:09:02 > 0:09:11But if they're hammered into a hole that is too tight, the shell could crack and then the acorn would rot.
0:09:13 > 0:09:21So maintenance is a never-ending, year-round labour, and it takes a lot of care and judgment.
0:09:34 > 0:09:37The result is a great acorn treasury
0:09:37 > 0:09:41that will last the whole family well into the next harvest.
0:09:44 > 0:09:48These neat holes are made not for storage, but for theft.
0:09:48 > 0:09:53They're made by another kind of woodpecker - a sapsucker.
0:09:56 > 0:10:02They're just deep enough to tap the vessels along which the tree transports its sap,
0:10:02 > 0:10:07and sap is largely what the sapsucker lives on.
0:10:09 > 0:10:17The bird cuts its sap wells with an accuracy and symmetry that would do credit to the finest cabinet-maker.
0:10:34 > 0:10:40Sap normally hardens quickly and seals a wound. This doesn't.
0:10:40 > 0:10:46It could be that the sapsucker produces a kind of anticoagulant in its spittle,
0:10:46 > 0:10:51but if it does, no-one yet has managed to identify it.
0:10:51 > 0:10:58Even so, each little well eventually runs dry and the bird has to cut another.
0:11:03 > 0:11:10These wells have been made in the trunk of a pine tree which produces sap throughout the year.
0:11:12 > 0:11:20Other trees, such as these aspens, only produce sap in quantity during spring and summer.
0:11:20 > 0:11:25When the sapsucker moves on to these, it cuts differently shaped wells.
0:11:35 > 0:11:41With this spring increase in the sap supply, new birds appear in the woods.
0:11:41 > 0:11:49A yellow-rumped warbler. They're quick to drink from the wells cut by the sapsuckers.
0:11:49 > 0:11:53Food is short so early in the year.
0:12:02 > 0:12:05The birches are now in leaf
0:12:05 > 0:12:12and the sapsucker moves on to them and makes wells of yet a different shape.
0:12:25 > 0:12:32A northern oriole - another hungry migrant only too willing to benefit from the labours of others.
0:12:32 > 0:12:34And a hummingbird.
0:12:34 > 0:12:43It used to be thought that hummers timed their arrival to coincide with the opening of the spring flowers.
0:12:43 > 0:12:52But they arrive well before that. Their appointment is with the rising of the sap and the sapsucker's work.
0:12:52 > 0:12:57Sap is an energy food, easily picked up with the tongue,
0:12:57 > 0:13:04but it can only be collected from many northern trees during part of the year,
0:13:04 > 0:13:12so when winter approaches, warblers and hummingbirds fly south again to where it's winter all year long.
0:13:12 > 0:13:18Here, in Mexico, the sap is taken not only by birds, but by insects.
0:13:18 > 0:13:22The trunks of many trees seem to be sprouting long hairs.
0:13:22 > 0:13:26At the end of each, there's a tiny drop of liquid.
0:13:26 > 0:13:33The hair is a tube, projecting from the rear of an insect, lying beneath the bark, drinking sap.
0:13:33 > 0:13:38But the insect gets more sugar than it needs, so it excretes the excess.
0:13:40 > 0:13:46That is what the hummingbirds, with exquisite accuracy, manage to collect.
0:14:03 > 0:14:06Many different warblers take it, too.
0:14:22 > 0:14:27The liquid, rather flatteringly called honey dew, is so sought after
0:14:27 > 0:14:35that some birds take up residence in a particular tree, and will drive away any others that try to feed.
0:14:35 > 0:14:42Their meals, however, come in such small instalments that feeding has to be almost continuous.
0:14:44 > 0:14:49It takes about an hour for a drop to accumulate at the end of a tube,
0:14:49 > 0:14:58so to get enough to sustain themselves, the hummingbirds have to travel round throughout the day.
0:15:11 > 0:15:16Plants produce other edible things as well as seeds and fruit and sap.
0:15:16 > 0:15:24They sprout leaves, but leaves are not very good food. They're bulky and need a lot of digesting.
0:15:24 > 0:15:30So animals that live on leaves, like these cows, for example,
0:15:30 > 0:15:37tend to be rather hefty creatures with massive batteries of grinding teeth and special capacious stomachs.
0:15:37 > 0:15:45Cows, having grazed, lie down and bring up each mouthful for a second grinding chew.
0:15:45 > 0:15:52No bird does that - you can't chew with a beak. Geese have to use a different technique.
0:15:52 > 0:15:57They're big birds, as they have to be to accommodate such bulky meals.
0:15:57 > 0:16:02Rather than digest grass intensively they eat a great deal of it,
0:16:02 > 0:16:05and get rid of what they can't digest almost immediately.
0:16:19 > 0:16:23The appetite of geese is apparently never-ending,
0:16:23 > 0:16:30and a flock of them, like these barnacles, will work its way across a meadow nibbling non-stop
0:16:30 > 0:16:34and pooping all the way.
0:16:34 > 0:16:40It's a terrible mess, but it means that after feeding for several hours
0:16:40 > 0:16:45the geese are not laid down by great quantities of undigested grass...
0:16:45 > 0:16:50and can get into the air without much difficulty.
0:16:59 > 0:17:05In South Africa, there's a rather smaller leaf-eater, the mousebird.
0:17:05 > 0:17:11They do make some attempt to digest their meals a little more thoroughly.
0:17:11 > 0:17:14They start feeding early in the day.
0:17:32 > 0:17:36Then, with as much nibbled leaves on board as they can manage,
0:17:36 > 0:17:44they sit for hours with their distended stomachs turned towards the sun to help with digestion.
0:17:46 > 0:17:50You can't beat a siesta after a heavy meal.
0:17:54 > 0:18:03In all the bird kingdom, there's only one species that is really specialised for leaf eating -
0:18:03 > 0:18:06the hoatzin of South America.
0:18:06 > 0:18:10Like a cow, it has two compartments to its stomach,
0:18:10 > 0:18:15the second of which is full of bacteria that help ferment its meals.
0:18:21 > 0:18:27In consequence, it's a bulky bird and positively clumsy in the air,
0:18:27 > 0:18:31more a lumbering cargo plane than a super jet.
0:18:34 > 0:18:41Birds, by stripping leaves, eating seeds and drinking sap, are exploiting plants,
0:18:41 > 0:18:44stealing from them.
0:18:44 > 0:18:49But many plants exploit birds by using them as couriers.
0:18:49 > 0:18:54The arrangement is such an ancient one
0:18:54 > 0:19:00that both have evolved special ways of transacting their business.
0:19:00 > 0:19:06The plants attract their couriers with flowers and pay with nectar,
0:19:06 > 0:19:12which is easy and cheap to produce - it's water with a dash of sugar -
0:19:12 > 0:19:14and that's what I've got in here.
0:19:14 > 0:19:18These Australian rainbow lorikeets love it.
0:19:20 > 0:19:25Here, in Australia, there are some plants that are in flower all year,
0:19:25 > 0:19:32so it's possible for birds to specialise as nectar-feeders, as these lorikeets do.
0:19:32 > 0:19:36Their tongues, instead of being hard and leathery,
0:19:36 > 0:19:40have a feathery, brushy tip so they can lap up the nectar.
0:19:40 > 0:19:46And the plants, when they have a need for a messenger, advertise the fact
0:19:46 > 0:19:51by producing flowers with particularly bright petals.
0:19:53 > 0:19:58Having collected all the nectar immediately available on one tree,
0:19:58 > 0:20:01the lorikeets move off to another,
0:20:01 > 0:20:06carrying the pollen they collected with them.
0:20:06 > 0:20:15But if, as here, the next plant they visit happens to be a different one, the pollen will be wasted.
0:20:15 > 0:20:19The plant's way of reducing that risk
0:20:19 > 0:20:27is to recruit an exclusive service with couriers who, during flowering season, will visit them alone.
0:20:27 > 0:20:35Here, in South Africa, this species of heather encloses its nectar in a kind of floral safe
0:20:35 > 0:20:41which only a particularly shaped beak can unlock.
0:20:41 > 0:20:46This orange-breasted sunbird has a beak of that shape,
0:20:46 > 0:20:50but, even so, it has to probe really deeply for the nectar,
0:20:50 > 0:20:56and every time it does, it triggers a little explosion of pollen.
0:20:59 > 0:21:05When the bird drinks at another heather plant, some of that pollen will be brushed off,
0:21:05 > 0:21:09and the heather will have achieved its end.
0:21:13 > 0:21:17But bird and flower can fit one another more closely than that.
0:21:17 > 0:21:25On Mount Kenya, there's a sunbird with an even more strongly curved bill - the golden-winged sunbird.
0:21:35 > 0:21:41And this is its employer - the lion's claw flower.
0:22:04 > 0:22:09The feathers on the sunbird's head look golden, like those on its wings,
0:22:09 > 0:22:12but not so - they're black.
0:22:12 > 0:22:19The gold colour is entirely due to pollen which is stamped on it when the bird thrusts deep in the flower.
0:22:30 > 0:22:38The devices used by plants to restrict their payments to their employees
0:22:38 > 0:22:42may, if taken to extremes, defeat the object of the exercise.
0:22:42 > 0:22:51This South American plant has gone to great depths to shield its nectar from all but its established partner,
0:22:51 > 0:22:54and that has encouraged burglary.
0:22:54 > 0:22:57This is the black flower piercer.
0:23:02 > 0:23:09It knows exactly where the nectar is stored and it knows a quick way of getting it too.
0:23:16 > 0:23:23Its tongue is flicking into the nectary at the top of the flower's trumpet,
0:23:23 > 0:23:28so that the nectar is channeled down its lower bill into its throat.
0:23:36 > 0:23:40The datura has even longer flower trumpets,
0:23:40 > 0:23:43but they are robbed just as easily.
0:23:48 > 0:23:52In S America, hummingbirds are the main collectors of nectar,
0:23:52 > 0:23:57and they will collect it any way they can -
0:23:57 > 0:24:04utilising a flower piercer's break-in is as good a way as any other, as far as they're concerned.
0:24:20 > 0:24:28The trumpet of the datura is so long you might think nothing could drink from it legally, as it were,
0:24:28 > 0:24:32and only one bird can - the sword-billed hummer,
0:24:32 > 0:24:36which has the longest beak, proportionately, of any bird.
0:24:36 > 0:24:40A plant only flowers for a short period each year,
0:24:40 > 0:24:45so a nectar drinker has to have a succession of suppliers.
0:24:45 > 0:24:50The swordbill also drinks from passionflowers.
0:24:50 > 0:24:58The S American climate is so equable and the number of plants so huge, there are always flowers to be found.
0:24:58 > 0:25:05Accordingly, hummingbirds have been able to evolve highly specialised equipment for nectar feeding.
0:25:05 > 0:25:12They developed a unique way of flying that lets them hang in the air while they drink from a blossom.
0:25:17 > 0:25:24Their tongues have become threads that flick in and out a dozen times a second,
0:25:24 > 0:25:29but they're virtually useless for collecting any other kind of food.
0:25:33 > 0:25:38Where most plants tend to bloom at the same time of the year,
0:25:38 > 0:25:46neither the suppliers nor the drinkers of nectar can afford to be so specialised.
0:25:46 > 0:25:52The coral tree, in Thailand, has no alternative but to offer its nectar in a free and open way,
0:25:52 > 0:25:59and this delectable seasonal treat attracts all kinds of birds from far and wide.
0:25:59 > 0:26:08Such a large and varied clientele is pretty well bound to do the job required of them.
0:26:41 > 0:26:50After they are pollinated, plants produce seeds and then many engage other birds to distribute them.
0:26:50 > 0:26:57That, by and large, is heavier work and the payments they offer for that are made with a different currency -
0:26:57 > 0:26:59fruit.
0:26:59 > 0:27:06Hornbills are on their way to do a job for a fig tree in the Indonesian rainforest.
0:27:31 > 0:27:37In Northern Europe and America, waxwings gorge themselves on autumn berries.
0:27:37 > 0:27:45A plant wraps its seeds in the minimum flesh needed to persuade a bird to swallow them.
0:27:45 > 0:27:51These berries have so little that it's quickly stripped off in the stomach,
0:27:51 > 0:27:57and then the waxwing can get rid of the indigestible seed.
0:27:57 > 0:27:59The story is the same the world over.
0:27:59 > 0:28:07In New Zealand, kokakos are great berry-eaters, distributing the seeds of the plants of their native forest.
0:28:07 > 0:28:16In South America, tiny wild avocados are the special favourite of one of the most dazzling birds, the quetzal.
0:28:18 > 0:28:25The avocados may be small, but they're still too big for the quetzal to swallow,
0:28:25 > 0:28:30so the stones are ejected, not from the back end, but from the front.
0:28:33 > 0:28:41The bird has had a good meal, and the avocado has had some of its seeds carried to a new site.
0:28:45 > 0:28:51There are other things to eat apart from the products of plants.
0:28:51 > 0:28:58They may be difficult to find and even more difficult to catch, but they're well worth having,
0:28:58 > 0:29:03because they're full of nutrition - things, for example, like this.
0:29:04 > 0:29:09The morpho - a big and powerful butterfly.
0:29:13 > 0:29:17The jacamar - a cousin of the kingfisher's.
0:29:27 > 0:29:31A butterfly's wings aren't very digestible
0:29:31 > 0:29:37and have to be stripped off before the bird can swallow the fat nutritious body.
0:29:45 > 0:29:52Winged termites erupting from their holes in the ground and flying away to establish new colonies -
0:29:52 > 0:29:55a whole host of birds relish these.
0:30:00 > 0:30:05Ants are trickier meals - they, after all, can sting.
0:30:08 > 0:30:12It takes a specialist to deal with them.
0:30:12 > 0:30:17This is the rufous woodpecker of Southern India.
0:30:17 > 0:30:22It's as good at drilling into an ants' nest as it is at drilling wood,
0:30:22 > 0:30:28and the bird seems totally indifferent to the ants' stings.
0:30:28 > 0:30:36The feathers of its tail, like those of all woodpeckers, are particularly stiff,
0:30:36 > 0:30:38so that they can serve as a prop.
0:30:38 > 0:30:45The most nutritious morsels are the soft, fat, stingless grubs that can be found in the centre of the nest.
0:30:51 > 0:30:55Insects are almost everywhere on every tree -
0:30:55 > 0:31:00on twigs, in buds, crawling around in crevices of the bark,
0:31:00 > 0:31:06and many birds find quite enough to sustain themselves just by looking carefully.
0:31:12 > 0:31:16But some work harder - and get greater rewards.
0:31:16 > 0:31:21The nuthatch, in European woods, is indefatigable.
0:31:21 > 0:31:28It will eat many things, including seeds in autumn and winter, which they crack with a workmanlike beak,
0:31:28 > 0:31:32but, in summer, insects are a major part of its diet.
0:31:32 > 0:31:37Its beak serves equally well for picking them out of the bark.
0:31:54 > 0:32:00The great spotted woodpecker is a little more specialised.
0:32:00 > 0:32:07It particularly likes the grubs of wood-boring beetles. First, it has to chisel away the bark.
0:32:26 > 0:32:31Its tongue extends for an inch-and-a-half beyond its beak
0:32:31 > 0:32:34and has a harpoon at its tip.
0:32:44 > 0:32:48When that hits a grub fair and square, it sticks.
0:32:53 > 0:32:59Tree-boring insects are never safe when woodpeckers are around.
0:32:59 > 0:33:06But woodpeckers never got to the Galapagos, far away from anywhere in the Pacific.
0:33:06 > 0:33:13Insects did, though, and their grubs bore into trees here just as they do everywhere else.
0:33:13 > 0:33:19But no Galapagos birds have the physical adaptations with which to reach them.
0:33:19 > 0:33:23Galapagos finches, however, are both intelligent and ingenious.
0:33:23 > 0:33:27Their beaks are perfectly adequate for stripping away bark.
0:33:41 > 0:33:46There's a grub under there somewhere. It can hear it.
0:33:46 > 0:33:50How, without the woodpecker's long tongue, can it get it out?
0:33:50 > 0:33:54It needs a tool - a spine from a cactus.
0:34:23 > 0:34:26A success, but only a partial one.
0:34:26 > 0:34:30It has only extracted little bits of the grub.
0:34:30 > 0:34:38Nearby, a bird from another clan of finches uses a slightly different technique.
0:34:39 > 0:34:48It selects a rather stouter tool that can be used not so much for stabbing as for levering.
0:34:55 > 0:35:00That has shifted the grub a little nearer the hole.
0:35:00 > 0:35:04It's not quite within reach, but it still has its lever.
0:35:04 > 0:35:07Give it another go.
0:35:30 > 0:35:33And that's got the rest of it.
0:35:33 > 0:35:40Another remote and isolated island on the other side of the Pacific - New Caledonia.
0:35:40 > 0:35:47It gets a lot of rain, so it has a much bigger and richer forest than the Galapagos.
0:35:47 > 0:35:54But even so, it's so far away from any of the major continents that woodpeckers have not got here either.
0:35:54 > 0:35:58This fallen tree trunk is studded with holes,
0:35:58 > 0:36:01the work of wood-boring beetles.
0:36:03 > 0:36:11Their size suggests that they're made by much bigger insects than their equivalent on the Galapagos.
0:36:19 > 0:36:26The New Caledonian crow - and crows are among the most intelligent of birds.
0:36:26 > 0:36:33Once again, the sound of a grub, gnawing away in its burrow, betrays its presence.
0:36:38 > 0:36:45And once again, since this grub-hunter hasn't got the woodpecker's long tongue,
0:36:45 > 0:36:48a tool is needed.
0:36:59 > 0:37:05To contact this grub, the stick will have to be thrust in really deeply.
0:37:31 > 0:37:34A spectacular catch.
0:37:43 > 0:37:51Some of these crows become so attached to one particular tool that they carry it about with them.
0:37:53 > 0:37:58This log is clearly a good source of grubs,
0:37:58 > 0:38:03and a whole group of crows have come here to feed.
0:38:08 > 0:38:12Their technique is neither to stab nor to harpoon,
0:38:12 > 0:38:16but something more subtle - to irritate.
0:38:21 > 0:38:27This grub has got big jaws and, if attacked, it can give a powerful bite.
0:38:32 > 0:38:35And that's what the crows rely on.
0:39:21 > 0:39:27A younger bird joins an experienced adult to see how things are done.
0:39:49 > 0:39:52Now the pupil has a chance.
0:39:56 > 0:40:00It hasn't got all the details exactly right.
0:40:00 > 0:40:04It will be about a year before it masters the skill.
0:40:14 > 0:40:18There are insect grubs everywhere of course.
0:40:18 > 0:40:23The only problem for insect-eating birds is getting at them.
0:40:23 > 0:40:26Sometimes, other creatures help.
0:40:46 > 0:40:51You might think that this is a recent partnership,
0:40:51 > 0:40:59but I'll bet, when our prehistoric ancestors first dug for tubers and planted seeds in Europe,
0:40:59 > 0:41:03one of these little robins appeared within a couple of days.
0:41:03 > 0:41:10Other animals must have done the same job for them before human beings did.
0:41:10 > 0:41:15Once, not so long ago, wild pig were common all over Europe,
0:41:15 > 0:41:19and they are great diggers and rootlers.
0:41:23 > 0:41:29So maybe the robin's boldness and friendliness with other kinds of animals
0:41:29 > 0:41:35started in prehistory, even before human beings arrived in Europe.
0:41:46 > 0:41:52Such partnerships exist everywhere, even in the most unlikely places.
0:41:52 > 0:41:57This little bird lives on a small island in the Seychelles,
0:41:57 > 0:42:02so small and so isolated that few mammals got here before human beings.
0:42:07 > 0:42:15It's not, in fact, closely related to the European robin, but it behaves like one.
0:42:15 > 0:42:22When Europeans first came to the Seychelles, they called it a robin because of its similar habits.
0:42:22 > 0:42:27But what partner did it have before human beings came along?
0:42:31 > 0:42:33Could it be this?
0:42:43 > 0:42:49Once, there was a large population of these giant tortoises on several of the Seychelles islands.
0:42:49 > 0:42:53They weigh several hundredweight,
0:42:53 > 0:42:58and those huge legs dig into the ground with every step.
0:43:00 > 0:43:03There we are!
0:43:03 > 0:43:09These little birds, rarer now than the tortoises, are still their regular companions.
0:43:15 > 0:43:17A swamp in South America -
0:43:17 > 0:43:25an abundance of water and a warm tropical sun make it a paradise for insects of all kinds.
0:43:25 > 0:43:29A kind of flycatcher - a cattle tyrant -
0:43:29 > 0:43:34and another obliging partner, a capybara,
0:43:34 > 0:43:37a large semiaquatic rodent.
0:43:37 > 0:43:44As the capybara moves around, it inevitably disturbs insects of one kind or another,
0:43:44 > 0:43:50and what better place for an insect-eater to spot them than sitting on the back of one?
0:44:28 > 0:44:33Would the view be any better from there?
0:44:39 > 0:44:42Perhaps it would be.
0:45:06 > 0:45:14A few of these partnerships between birds and other animals have become very intimate indeed.
0:45:14 > 0:45:19The hide of a hippo may not seem a particularly rich insect source,
0:45:19 > 0:45:24but there are little ticks to be had in the various cracks and crannies,
0:45:24 > 0:45:29and oxpeckers go there to search for them.
0:45:37 > 0:45:45They have extremely sharp claws with two toes pointing forwards and two backwards,
0:45:45 > 0:45:49so they can cling at any angle - even on a slippery hippo.
0:45:58 > 0:46:04Land animals with hair on their hide are likely to be more productive.
0:46:04 > 0:46:08Oxpeckers pay particular attention to their ears.
0:46:08 > 0:46:14That's the sort of place you might find a tick, and the oxpecker will remove it.
0:46:14 > 0:46:16It also eats earwax.
0:46:18 > 0:46:22Dandruff is another part of their diet.
0:46:31 > 0:46:39Their beaks are flattened so that, with their head held sideways, they can comb through their hosts' hair.
0:46:44 > 0:46:49Oxpeckers spend all their lives on or closely beside their animal hosts.
0:46:49 > 0:46:51They court and mate on their backs.
0:46:51 > 0:46:56When they fly off to make a nest, as they must necessarily do,
0:46:56 > 0:47:04they pluck hair from their hosts' backs with which to line it. But do they do anything in return?
0:47:04 > 0:47:11It's true that they remove irritating, even damaging insects their hosts can't dislodge,
0:47:11 > 0:47:14but the birds' main diet is blood.
0:47:14 > 0:47:19Sometimes they get it by swallowing ticks that are bloated with blood,
0:47:19 > 0:47:27but they also take it directly, pecking at an animal's wounds to keep them open.
0:47:27 > 0:47:34When their host gets irritated, they go back to their toiletry duties, before once again having a sip.
0:47:37 > 0:47:45So, in spite of having such a specialised life, living on the bodies of mammals,
0:47:45 > 0:47:48oxpeckers manage to get quite a varied diet -
0:47:48 > 0:47:54a maggot or a tick, a little sip of blood, some tasty earwax -
0:47:54 > 0:48:00but there are some birds that literally live on mammals, alive or dead.
0:48:00 > 0:48:08They eat them, and those are the birds we'll be looking at in the next programme in this series.
0:48:31 > 0:48:36Subtitles by Martin Maguire BBC Scotland 1998