Watching Bird Behaviour
The study of bird behaviour involves the study of a bird’s reactions to objects and situations it meets in everyday life. It is easy to see what a bird is doing but you have to be very careful about interpreting what you see. Quite often bird-lovers try to interpret the behaviour into human terms. You often hear people saying that a Robin or thrush is a devoted mother or that a Robin is happy because he is singing. However, the people who make these remarks fail to realize how complicated the human mind is compared to that of the bird, and how much of their behaviour is instinctive and the result of a little learning.
Most behaviour patterns are instinctive and are performed without any preliminary experience or learning. From the moment that a bird in its egg starts to cut its way out, or to stretch up its head in the nest and open its beak, it is acting instinctively. It knows when to migrate, where to migrate to and in the following year how to build a nest and reproduce. All these instincts connected with reproduction, feeding and migration are inherited and whilst this innate behaviour usually serves the bird well, almost all these activities can be improved as the bird learns through experience. Although since the bird has a small brain its capacity to learn is limited. Instinct, therefore, is the inherited or innate tendency to act in a certain way in response to a certain situation. The behaviour pattern is almost as stereotyped and as flexible as is the innate tendency for an animal to be of a certain size, shape or colour. The basic ‘themes’ of bird song are instinctive. Most young birds act instinctively to the alarm notes of the parents, even when the parent may have different alarm notes for different dangers.
This instinct generally helps the individual to survive; innate behaviour comes from survivors and generally will be passed on further. Innate behaviour usually occurs in somewhat stereotyped patterns which are called, fixed behaviour patterns. They are very constant in form, and are triggered by stimuli around them which Konrad Lorenz called releasers. However, for various reasons, birds normally only react to any one of these stimuli at appropriate moments. Even so, releasers will not trigger off fixed behaviour patterns until the bird has been motivated; a specific motivation is often called a drive. Thus a bird which is motivated by hunger is probably highly responsive to food stimuli and so on.
I think I should try at this point to bring some of these technical terms to life. Going back to the concept of releasers, in spring it is fairly easy to see how a Robin’s red breast triggers off aggressive activities in other Robins defending their territories. Exposure of the white rump of Bullfinches or the white outer tail feathers of a Chaffinch, trigger off flight in other Bullfinches or Chaffinches feeding close by. The red patch on the Herring Gull’s bill is the releaser that will trigger off the feeding behaviour pattern of begging for food by a young bird activated by the hunger drive.
In adults, a build-up towards the activation of an innate behaviour pattern towards a specific goal involves exploratory activities which are technically known as appetitive behaviour. For instance, in the early stages of nest-building birds will often pick up pieces of nest material, play with them in their bills for a while and then drop them. As the drive develops the birds will finally select a nest site and begin to build, picking up and finally inserting a piece of material into the nest, in what is called the consummatory act.
Birds are subject to many different drives every day but normally only one or other of them can be dominant at any particular time. The intensity of a drive may depend on many factors both internally and externally.
Derived from these fixed behaviour patterns are a number of other activities: for instance, at certain times of stress a bird or animal may perform a behaviour pattern entirely out of context. This often occurs when there is a conflict between different drives. When two birds, for example, are displaying to each other in an attempt to establish a territory a conflict may occur between the drive for fighting and the drive to escape. These two drives are incompatible. As neither can be discharged through its normal consummatory act, the tension within the bird may find release in irrelevant behaviour and one or both may start preening or picking up nest material, bill-wiping, bathing, false brooding of young or pretending to sleep. These are all outlets through which the thwarted drives can express themselves in some form of motion, and are called displacement activities.
Intention movements are a second type of derived activity. They represent the initial phase of some appetitive behaviour and differ from displacement activities in that they are caused by the drive of their own behaviour patterns but are only of low intensity. One of the most obvious intention movements, which anyone can see, occurs when a bird prepares to fly or when it is disturbed by somebody or an enemy some distance away. Before the bird actually flies it may bend its legs, take the wings away from its body feathers and raise its tail.
A third type of derived activity is known as a redirected activity. This is directed towards an object or animal other than the one releasing it, although the actual releasing object or animal is available as a target at the time. For instance, in a territorial battle the owning bird stops attacking the intruder and begins pecking vigorously at the ground. Quite often Wheatears that I have studied would peck at the ground and tear up grass excitedly in a manner quite different from the way they collected nest material. On one occasion, on Skokholm, one of the bigger, so-called, Greenland Wheatears established its own small territory within the breeding territory of a pair of Wheatears close to their nest. The resident male attacked the larger intruder fairly continuously for a day or so and then gave up. From that moment onwards his own mate attacked him constantly and gave up collecting nest material and building her own nest, until after three or four days the bigger Wheatear moved on.