1 Preliminary examples
The best way to start is by thinking about the following two case studies.
Case Study 1: Flocking and migrating birds
At one time or another, you will have witnessed the sight of a flock of birds, maybe hundreds strong, wheeling in the sky. Perhaps you didn’t give it a second thought, but bird flocking does seem quite a mysterious phenomenon. The birds all keep formation, change course together, steer on the same heading. They seem to be moving as a single group, but there is no leader, no observable external guidance and no obvious way in which the birds might be communicating across the flock.
Even more striking is the phenomenon of migration. Most bird species migrate northwards in the spring to breed, and south in the winter to warmer climates where food will be plentiful.
Some species travel by day, others by night; some fly in immense flocks, others alone. Many cover enormous distances: the arctic tern (Sterna paradisaea) migrates from Maine in the USA to the coast of Africa and then down to the Antarctic Circle, travelling as much as 35,000 kilometres a year. Most breeding and wintering grounds cover relatively small geographical areas, yet the birds find their way to them unerringly, year after year. For example, the greater snow goose (Chen caerulescens atlantica) breeds in a very specific region of the Canadian High Arctic, from the Foxe Basin to Alert on northern Ellesmere Island. They winter along the United States Atlantic coast, migrating more than 4000 kilometres, in flocks of between 35 and 1000 birds, depending on the season.
How birds are able to navigate with such accuracy is not fully understood, but most species are thought to use a number of range- and direction-finding strategies, including:
- steering by visual landmarks such as coastlines, rivers or mountains;
- setting flying courses by the sun (especially at sunset) and stars (especially the Pole Star and the constellations around it);
- following the Earth’s magnetic field: iron-based minerals in birds’ skulls enable them to fly north along magnetic field lines.
Some birds, such as petrels, also use their sense of smell to navigate, but only as a supplement to the mechanisms described above.
Case Study 2: Raiding army ants
The many species of carnivorous army ants (Eciton) live in colonies, maybe up to a million ants strong. Army ant nests are often referred to as ‘bivouacs’, because they are not earth constructions like those of other ant species – they are formed by the ants themselves, clustering together to form walls, fastening onto each other using their mandibles and claws on their legs. Despite being more or less blind, army ants search for prey in immense, highly organised groups – either swarms or columns, depending on the species. In a column raid, the ants spread out from the colony along a single trail from which foraging worker ants branch off along smaller columns. A swarm raid also starts along a trunk trail, which divides into numerous columns that then recombine into a single advancing swarm front.
For regularity, organisation and sheer savagery, nothing quite matches the swarm raider (E burchelli): a single colony may consume 100,000 prey items a day and bring back as many as 30,000 from a single raid. At dawn, pioneer ants set out, first along a base column connected to the bivouac and then fanning out in a complex network of columns along a swarm front up to 15 metres long and 2 metres deep. Individual ants move forward from the front and then retreat; and as each ant turns, another passes it, extending the front further.
Smaller insects – and even relatively huge creatures such as cockroaches, scorpions, grasshoppers and earthworms – are flushed out, overwhelmed and stung to death by the advancing mass. Their corpses are sawn up and the pieces transported back to the colony by streams of workers along a labyrinth of trails behind the main front. Unbelievably, army ants have been observed to kill and dismember chickens, goats and even pigs, if the animals have previously been injured and are already helpless.
From your own general knowledge, try to think of one or two other examples of similar behaviour to that described in the above case studies.
One doesn’t have to be a zoologist to know that examples abound. Birds and termites build complicated nests. Whales and bees carry out remarkable feats of navigation and communication. Fish and mammals such as wildebeest travel and defend each other in apparently organised schools or herds.
What seems significant about behaviours like these, as compared to some other natural process, such as an avalanche, the flow of a river, the piling up of rocks by a glacier, etc? Note down some general characteristics that both the above case studies seem to have in common.
Obviously there are key differences between the behaviour of an ant swarm, say, and an avalanche or any other purely physical phenomenon. First, the swarm seems to be purposeful: all that activity is unmistakably directed towards a clear end – the feeding of the colony. The same is true of the movement of birds. This certainly can’t be said of avalanches, rivers, and so on: their actions seem to be governed by chance and the results are haphazard. Second, the behaviour of the animals in the case studies looks systematic. At first glance, an ant raid might look like a boiling confusion but, as we have seen, it follows a very regular pattern; so too do the flight patterns of the birds. Such activity can lead to complex and structured results, such as the elaborate nests of termites or birds.
There can be no argument that the natural world is full of such purpose and order. But purpose and order are surely two characteristics we might associate with intelligent behaviour.