Animal Behaviour - Feathered Einsteins, Mischievious Meerkats and Monkey Vision

Have you ever wondered why humans walk on two legs, while pretty much all other animals prefer four?  Most human evolution researchers think we started to walk upright through a process beginning with "knuckle walking" on land - the way that chimps and gorillas (and maybe some of the Naked Scientists team!) walk today.

This change was thought to have happened when our ancestors left the forests of East Africa and moved onto the grasslands. But researchers from the University of Liverpool have come up with some evidence to suggest that we actually learned to walk upright by foraging in treetops for food, in a paper published in the journal Science.

Their studies of Sumatran orang-utans have led them to the conclusion that knuckle walking is quite a recent development for chimps, and that the ancient great apes actually spent more time on two legs in trees, holding onto branches for support.  So us humans may never have gone through a knuckle dragging stage at all, and skipped straight from tree living to two feet on the ground.

One of the researchers, Professor Robin Crompton explains that "Walking upright on two legs, gripping branches with the feet and balancing themselves by holding or touching higher branches with their hands is actually a very effective way of moving on smaller branches. It helps to explain how early human ancestors learnt to walk upright whilst living in the trees and how they would have used this way of movement when they left the trees for a life on the ground."

US researchers have found that canny moths impersonate the sounds made by their bad-tasting relatives to ward of bat-attacks.

Writing in this week's PNAS, Jessie Barber, from Wake Forest University, trained two species of bats to hunt for moths within sight of two infra-red enabled video cameras. At the same time he recorded the sounds produced by moth prey and the hunting bats. In response to hearing the sonar emitted by bats to locate their meals, some unpalatable tiger moths use a pair of structures called tymbals to broadcast ultrasonic clicks of their own, which are designed to warn the hunter that they taste bad. The bats then duly avoid them. But other tastier moths appear to have muscled in on the trick to avoid being eaten and mimic the bat-repelling sounds with good effect: "we found that bats do not eat the good-tasting moths that make the similar sounds," said Barber. Moths that exercised the right to remain silent, on the other hand, fared less well and were instantly gobbled up.

The Blue Whale is the loudest animal in the world and it makes a sound up to about 188dB. For comparison, a jet engine at take off is about 140 dB, and the human pain threshold is about 120dB. Humpback Whales are not as loud, but they're more like the Mariah Carey of the whale world as they have really complex whale songs with a really wide frequency range.

The amplitude of whale song is measured underwater, so although it would be painful to humans, it doesn't hurt other animals in the sea because they have different ears and can tolerate such high amplitudes.

Now to the Kalahari Desert and the study of the most co-operative mammals of all, the Meerkats.But what's the basis of their society and how is it organised? We spoke to Professor Tim Clutton-Brock from Cambridge University about his work with the Kalahari Meerkat Project.Tim - I've worked on Meerkats now for 13 years and we've managed to tame up, habituate, 14 different groups of Meerkats so we have about 300 animals in the Kalahari which is where we work, and each of those groups, the groups of somewhere between 10 and 40 animals in each group, each has a separate territory of about somewhere between five and ten square kilometres. And we can recognise all those individuals and we have got them so tame that they'll actually climb onto electronic balances at request, so we've trained the Meerkats for crumbs of hardboiled egg to get onto the balances.Chris - What are you ultimately hoping to find out by doing this?Tim - I think the single focus of the study is why they're so co-operative, so the Meerkats are arguably the most co-operative mammal, perhaps it's a near-run thing between them and naked mole rats but Meerkats are very, very co-operative. One female in each group breeds and everyone else in the group helps to rear her pups, males and female group members, fully mature individuals, fully mature males, baby-sit the pups. They help to get food for the pups, they guard the pups, they go on guard in turn so the group is breeding as a unit not unlike an insect society.Chris - How do they decide who is the dominant female?Tim - When you remove a dominant female, all the potential other females compete like fury, they fight commonly, and then one finally emerges and she suppresses the others, she commonly evicts the main challengers over the next few months, and then she turns in and produces children over, oh, it can be five to ten years, so the group gradually becomes a dominant female and the male she's mated to and her children.Chris - So how do they persuade all of their other members of their colony to rear their own, well, the children of the animal that's breeding at the expense of breeding themselves?Tim - Well, that's a very good question. They stop the other females breeding so the presence of the dominant female actually suppresses their fertility so the others can't breed. If they do breed, and they do occasionally, the dominant female commonly kills and sometimes eats their pups.Chris - So that's a pheromonal suppression, is it?Tim - It's probably a pheromonal suppression. It may also be partly through direct interaction because the dominant females are aggressive towards the other females. The other way they help to suppress is that when at particular stages of the breeding cycle, they throw the oldest female subordinates out of the group so one way of getting your daughter to help in Meerkats society is to sling her out into the outside world so she sees just how tough that is and then when she comes back in she's prepared to do the washing up.Chris - I know a few humans who can benefit from that strategy, but quite complicated behaviour. Where do they get it from?Tim - I think the co-operation is associated with desert living and with diurnality, with the fact that they're active during the daytime and if you live in an open desert and you're active during the day, you're very, very susceptible to predators and you've got to come up with some way of combating predators and groups defend each other against predators, they put on guards to keep an eye out, they keep a huge network of burrows as escape systems from predators, so the group is very, very important in keeping predators out.

Dr Andrew Smith works with Tamarin monkeys in South America and the endangered Buton macaque with Operation Wallacea in Indonesia.

Chris - Tell us about this work on how monkeys use colour, and why this is relevant to us.

Andrew - Certainly, I've been researching on primate colour vision. It's an interesting topic because primates unlike the majority of animals have got three cone colour vision, which means they can see the same range of colours, more or less, as we can. Non-primate mammals such as dogs and cats see the world in a reduced set of colours, and we weren't entirely sure why this was the case.

Chris - People often say that dogs see the world in black and white, but that's not true. A dog sees the world in colour, but probably akin to how a colour blind human would see.

Andrew - Exactly, if you imagine a dulux colour chart, it's just a reduced set of those colours, not being able to distinguish certain combinations of those, rather than simply seeing the world in black and white or 'an other colour' and white.

Chris - So how was it first discovered that monkeys and other primates did have this ability, it wasn't just us?

Andrew - What they were doing was looking at colour vision capabilities by giving them more or less the same tests that they were giving humans; basically asking them to discriminate between different coloured shapes. If they could tell the difference between the colours then obviously they can tell that those are separate and distinct colours.

Chris - So it's set up so that there's no way they could do that by having two colour- they had to have three colour vision to do that.

Andrew - Yes.

Chris - So what's your view on the reason why they have got that ability?

Andrew - I think the main reason is probably due to foraging ability, so being able to detect fruit against a background of leaves. Leaves are invariably green, but many fruits when they're ripe - which is when plants want animals to eat them and also when they will contain the most amounts of sugars and nutrients, are often orange, yellow or reddish. The ability to distinguish ripe fruits from a background of leaves, which obviously if you are human and colour blind its likely that you have distinct problems telling the difference between red and green, if you cant do this it will be difficult for you to pick out red fruits against a green background. Evolving good three cone or trichromatic colour vision is going to enable primates to choose the ripe fruits against a green background of leaves.

Chris - Is that what we have to thank for the fact that we have such good colour vision?

Andrew - We think so. That's probably the leading theory although there are alternatives that maybe it has evolved to enable you to pick out very young leaves. Young leaves are much more nutritious, they've got less noxious secondary compounds in them than old leaves. For folivorous, leaf eating, monkeys such as howler monkeys or gorillas, and maybe our human ancestors, the ability to pick out the newest, youngest, tenderest leaves may have been a selective advantage for the evolution of three cone colour vision.

Chris - We're not herbivorous, we're omnivorous so we eat some meat but you would have thought that other animals, that actually spend their entire life eating leaves, are dependant on eating plants all the time just to survive. It would be even more important to them, wouldn't it? So why don't cows and sheep and goats have that ability?

Andrew - It's possible that cows and sheep simply haven't had the chance mutation to develop three cone colour vision, and also, being much larger animals they have to graze and consume much larger quantities. Also it really depends on the type of leaf you're talking about. The leaves in terms of primate colour vision are from tropical forests where predation pressure on the leaves is quite high, and interestingly they do flush through a kind of pinkish-red when they're new leaves. However in grasses, the new leaves are basically the same as, or very similar to the adult leaves.

Chris - Is it just fruit that they use this enhanced colour appreciation for or could there be other spin-offs?

Andrew - There could be other spin-offs; it may help to detect predators. If you think about the coats of many cats in rainforests, such as ocelots, margays, jaguars, or indeed leopards, the yellowish hues in their coats may be more easily distinguished if you've got good three cone colour vision.

Kat - Another thing that's important as well as being able to spot predators is to actually find somewhere safe top sleep when you're trying to avoid predators. How do monkeys cope with that when they're living in the wild?

Andrew - It certainly seems for the small monkeys, the tamarins from the Amazon that I've been looking at that, predation is probably one of the most important aspects of their ecology. What they do is try to find the most secure sites, usually high up in trees, often hidden by dense tangles of vegetation and lianas. Also the monkeys really use the sites very infrequently; they change their sleeping site almost every night. The longest I've ever known them to sleep in the same site for is three consecutive nights. This is probably to stop any predators in the area building up a search image and maybe smelling a distinct monkey scent from a particular tree that they've been sleeping in a lot. By changing their sleeping sites very frequently they're hoping to avoid predators.