Articles

Title: An Insight Into Bird Behaviour
Author: Duncan Butchart
Date: 2009/12/01

Upon seeing a bird, the first thing that a birdwatcher usually asks is: "What species is it?" But how many ask the next question:"What is the bird doing?" In some cases, the answer to the second question may actually provide a clue to the bird's identity. But at any rate, interpreting what a bird is doing and how it is interacting with its environment, is invariably much more interesting than simply naming it.

In simple terms, behaviour is the way in which an animal acts in order to ensure its survival. For example, the way in which birds respond to a predator has an immediate bearing on their existence. Individuals which react quickly stand a chance of escaping and going on to breed. This is all part of the 'weeding-out' process of natural selection, as behaviour which enhances the survival and success of the species is preferentially handed on to subsequent generations. Naturally, the way in which a particular species behaves is the result of a long history of evolutionary development.

Innate or learned?

Although most of what a bird does is genetically determined, most species show considerable learning ability. Nest building, flight, mate recognition and other behaviours are innate and consequently inflexible but, throughout their lives, birds pick up information about the environment and modify aspects of their behaviour accordingly. Young eagles often tackle prey which is too large for them and learn to avoid such dangerous quarry in later years (if they survive!), while mature eagles get to know their home range intimately and this can improve their hunting success. There can be no doubt that aspects of migratory routes are learned by young cranes, storks and other birds which follow adults on established flight routes.

The term 'behaviour' covers a wide variety of activities, and so it is useful to divide it into two categories. First, there is self-maintenance behaviour such as feather care and feeding which keeps the individual in good shape while having relatively little influence on other birds. Secondly, there is social behaviour which strongly influences the activities of other birds of
the same species.

Feather care

Feather care is of crucial importance to birds. Although all birds moult once a year, individual feathers are frail and a considerable amount of time is spent caring for them. Preening is the process where a bird straightens and smoothes its feathers by nibbling and stroking. A bird uses its bill to effectively 'zip up' feathers by straightening out the barbules. Bathing is another effective means of maintaining condition. Different birds bathe in different ways. Sparrows go about the task rather gingerly, while robin-chats and thrushes splash themselves vigorously. Even waterbirds bathe and flamingos can be seen to gather at freshwater inlets in their otherwise saline lake habitats. Where water is scarce, birds simply make use of dust, and some birds such as mousebirds and bee-eaters actually prefer dust to water. Although it may seem strange, dust particles serve to absorb sticky plant resins or juices.

External parasites

Another means of feather care is the removal of external parasites and this may be accomplished by basking in the sun, with feathers raised to expose bare skin. Another possible means of controlling mites, lice and other parasites is called 'anting', a behaviour whereby a bird picks up ants and places them in its foliage or simply lies down among ants near an active mound. The theory is that the ants spray formic acid which repels the parasites, but this requires further research.

Feeding

What a bird feeds upon is a direct result of its body form, in particular its bill shape, whereas feeding behaviour is how a bird locates it food and how it deals with it. The great diversity of bird species displays a similar great diversity of feeding techniques. Some birds, most notably the oxpeckers, have a symbiotic relationship with large herbivores which offer them a steady supply of ticks. Anyone walking through the African bush who hears the distinctive rasping call of an oxpecker can be quite sure that a giraffe, buffalo or other large mammal is nearby. Gregarious griffon vultures soar to great heights not only to obtain the widest range of visibility, but also to watch for the tell-tale movements of other scavenging birds below them. As one vulture drops down to investigate a possible meal, so it is rapidly joined by many others. Feeding in groups increases competition over the actual food, but enables its discovery in the first place. Furthermore, the larger number of vultures on the ground feeding, the greater the chance of detecting a predator which might take advantage of the heavy-bodied birds.

Mixed flocks

One fascinating feeding strategy among smaller insectivorous birds of forests and woodland is the formation of 'mixed flocks'. Pairs, individuals or parties of one species join others to move through the foliage and branches on a broad front. As the group of birds progresses, so insects and other invertebrates are disturbed and made available to the most agile or bestequipped. The more birds in the flock, the greater the chance of discovery. Competition is reduced to some extent by the
physical structure of different species. Flycatchers will hawk moths disturbed by ground-foraging thrushes, while thrushes snap up beetles which dive into leaf litter after being flushed by a flycatcher. This behaviour is especially advanced in South American birds with some species of 'antbird' foraging ONLY in mixed flocks ...locating one of these birds is sure to produce a host of species.

The breeding cycle

Other than the benefits of gregarious feeding, most social behaviour is aimed at breeding successfully. Almost all birds have an annual breeding season (for smaller birds, this typically coincides with the warmer months when insects, seeds and berries are most abundant) and male birds must then compete for (or maintain) territories. A mate must be attracted, a nest built,
eggs laid and incubated and enough food collected for the developing young. The young must also be safeguarded from predators, and this involves behaviour such as distraction displays to lure predators from the nest, or direct 'mobbing' of snakes or owls to drive them from the area. These activities invariably require close co-operation between the pair. Observation of the breeding cycle is undoubtedly one of the most interesting and rewarding aspects of birdwatching, but care
must always be taken not to disturb nesting birds (by making observations from within a hide or blind).

Role of bird song

For many woodland and forest birds, the standard method of maintaining a territory is through the declaration of 'ownership' via song. This serves to alert other birds of the same species that an individual is present in an area and that it should keep out. When you listen to a dawn chorus, what you are actually hearing is this vocal behaviour of the various territory holders. Birds of prey often declare their ownership of a territory by soaring high above and, in the case of the African Fish-Eagle and African Goshawk, they call while doing so.

Courtship

The business of attracting a mate leads to some of the most interesting and dramatic bird behaviour. Cranes engage in elegant courtship dances, while the rollers get their name from their aerial kamikaze tumbling display. With their jet black plumage and trailing tail feathers, male Jackson's Widowbirds gather in groups to display to females. The males first create a little cropped lawn in tall grassland, and then leap up and down around a central cone of taller grass. Females gather around to watch the performers and the most impressive dancer probably gets the girl!

Pair bonds and nest building

Maintaining a pair bond throughout the breeding season, and sometimes over the whole year, is done in various ways. Some birds habitually call in duet with the notes of each bird alternating to create an 'antiphonal' song. To the uninformed ear, the duet sounds like the call of a single bird. African bushshrikes have taken duetting to its highest development. Interestingly, these birds tend to live in dense habitats where such calling not only keeps the pair in contact, but also ensures that an outsider does not intrude. The actual building of nests involves time and industry. Although this is innate behaviour, there is evidence with weavers and other birds that experience is a factor. Collecting nesting material puts a bird at risk to predators, so secretive behaviour must be employed. Intriguingly, some birds turn aggressive paper wasps into 'security guards' by building their own nests in close proximity to those of the insects. In Africa, small seedeaters such as waxbills and mannikins are often seen doing this.

Co-operative breeding

One particularly fascinating kind of breeding behaviour is co-operative breeding. This is when a number of adults, in addition to the genetic parents, aid in the rearing of the young. First described by Alexander Skutch for the Brown Jay, in 1935, cooperative breeding has since been described in over 250 species. The phenomenon raises interesting questions: Who are these extra adults? Why are they not breeding on their own? And why are they raising another's young? With African helmetshrikes, a family comprising one breeding pair and 'helpers' which are offspring from previous seasons occupy a defined territory. The whole family assists with various duties, including territory defence, building the nest, and feeding the nestlings and fledglings. Studies have shown that young (inexperienced) birds fare better by staying at home, rather than moving to find a new territory. By helping to raise their brothers and sisters, these birds are effectively propagating their own genes.

Behaviour aids indentification

Observing the way in which a particular bird is behaving can provide a clue to its identity and all good field guides include details on each species' characteristic behaviour. It is often difficult to separate the many physically similar cisticolas from one another on sight alone, for example, the way in which the birds behave during display flights quickly reveals their identity. Immature Bateleur eagles (all brown in plumage) frequently scavenge from carcasses and feed alongside vultures, while the similar Brown Snake-Eagle never does so.

So many questions

The study of bird behaviour poses many interesting questions. There are numerous behaviours for which no clear explanation can be given, and others for which the meaning is disputed. For instance, who knows why the Black-shouldered Kite wags its tail so repeatedly when it sits on a hunting perch?