A Glimpse of Bird Behaviour - Locomotion of birds

Understanding ‘Behaviour’ and how it applies to birds. The behaviour that will be discussed in this article is locomotion.

Understanding ‘Behaviour’ and how it applies to birds

         Behaviour means: Anything that a person says or does

If we apply this definition to birds, everything they do - flying, feeding, vocalisations, defences, preening, etc. - is behaviour.
The important thing we need to know about behaviour is that every behaviour has a purpose. The purpose might be visible to us, or invisible, but it is always there. No behaviour is without purpose. (This applies for everything and everyone.)
So, naturally, the behaviours of birds are also governed by the purposes they serve: to get to a new location, get food, communicate, avoid danger, take care of itself, etc.
 
This series of articles will be exploring a few key areas of bird behaviour.
 
The behaviour that will be discussed in this article is locomotion of birds/ birds locomotion, organs for locomotion and mechanism of flight.
Locomotion is the movement from one place to another. If we consider birds, locomotion can be achieved by flying, hopping, walking, running and even swimming. Of these, the one that we often associate with birds is flying, even though not all birds are able to fly (consider the kiwi, penguin, emu, etc.). 

•    Flight

‘Flying’ is defined as moving through the air with wings. But it is not simply flapping the wings up and down. There is a whole lot of physics involved, and it is those mechanisms that decide the flight-related behaviours of a bird. (Refer Fascinating flight of the birds for more details on the mechanism of flight)

©Suyothami

For a bird to fly, there should be two main entities - lift & thrust. Lift is the upward force that counteracts gravity, keeping the bird in the air without falling down, and thrust is what propels the bird forwards.

To generate the ‘lift’, there should be enough airflow under the wings. Generating this airflow is the challenge, because merely flapping the wings isn’t enough. For smaller birds, this airflow can be generated with a small hop or jump. But larger birds need something more, and this ‘something’ depends on each group of birds.

For example:

-   Large birds like eagles and hawks, which often perch high up in trees, simply just drop down with wings extended. As they fall, the relative motion of air is enough to generate the lift for these birds.

-   Some birds (like egrets) flap their wings and jump upwards. But to do this, their legs should be strong enough.

-  Some birds don’t have such strong legs. So how do they manage? We can look at ducks to find the answer. Ducks flap their wings and run over the water (or land). When they achieve enough speed, lift is generated and they can take to the air. This sounds similar to planes in runways, right?

-  Very small and light birds, like the humming bird, need only to flap their wings very fast.

This process of initiating flight is called takeoff, the first stage of flight. More often than not, birds face the wind when they takeoff. In other words, the direction of takeoff is opposite to the direction of the wind. This is because facing the wind helps the birds to get a good airflow under their wings in the right direction, thereby making it easier to generate lift.

An egret jumping up, wings flapping©Bhavana Sivayokan

An Indian spot-billed duck taking to the air after a short run in the water 
©Bhavana Sivayokan 

After takeoff comes the ‘manoeuvring and stabilization’ stage of the flight. During this stage, there are several types of flight patterns followed by the birds.

These include:

-   Flapping flight: This is the usual flight pattern common to all birds, in which the birds flap their wings up and down, generating lift and thrust.

-  Gliding: Here, the wings are extended, not flapping, the bird moves in circles, gradually losing height. During gliding, the outstretched wings provide lift, while thrust is due to gravity. Bird of prey (such as the eagle), and seabirds (such as the tern) can be seen gliding.

-   Soaring: This is similar to gliding in that the wings are extended, not flapping, and the bird moves in circles. But, instead of losing height, as in gliding, the bird gains height while soaring. This height gain is due to the rising air currents, which the birds use to their advantage. As with gliding, birds of prey and seabirds can commonly be seen soaring.

-   Hovering: This is a special type of flight pattern, in which the birds flap their wings very fast, but stay one place. Here, although the wings are flapping, only lift is generated, not thrust. Hummingbirds are known for hovering, but sunbirds can hover for a short time as well.

-   The ability to hover depends on many factors, including size and wing mobility. That’s why only smaller birds can hover. Larger birds can sometimes appear to be hovering, but this is false hovering, because they fly slowly into a strong wind and hence appear to remain in one place. This is called ‘wind hovering’. 

The gliding flight of a Lesser black-backed gull ©Bhavana Sivayokan

The flapping flight of Greater flamingos ©Bhavana Sivayokan  

The final stage of flight is landing. Just like how takeoff is difficult for larger birds, landing is also difficult for them. To manage this, different birds have different strategies.

-   Smaller birds just decide on their landing spot, and then, while they come near it, they reduce their speed to near zero. It is then only a matter of putting the legs down on the landing surface.

-    Other birds, especially birds of prey, use their legs as a brake, to grab on to the desired perch.

-  Ducks and other water birds with weaker legs, however, usually prefer landing in water. A swan is unique in that it can land only in water. These birds circle the wind and gradually slow down to make the landing. Like with takeoff, landing is also made against the wind, in order to maintain the lift.

-   For some birds, landing is so difficult, that often their landing is not as graceful as other birds. The albatross is a great example for this. Its wings are extremely well suited for prolonged flight, and often at great speeds. Therefore, it is easier for the albatross to land in water, where high speed landings are possible. But, when they try to land on the ground, they often stumble forwards and land clumsily on their chests.

An Indian roller, using its legs as a brake 
©Bhavana Sivayokan 

A cormorant landing in the water ©Bhavana Sivayokan 

•   Other modes of locomotion

Almost all birds appear to have at least two mode of locomotion. Most birds can fly. In addition to that, they also have a terrestrial locomotion mode (walking, running, hopping). Many birds can also swim. These other modes of locomotion used by birds depend on the individual characteristics of the species, including their size, leg strength, anatomy of their legs and wings, habitat, diet, etc.

-   Most birds walk, putting one foot in front of the other.

-  Smaller birds hop. Maybe because they can move greater distance with a hop than by walking. This is what is referred to as ‘economy of effort’.

-  Some larger, stronger birds (such as the ostrich and emu) can run with astounding speed.  (The ostrich can run at a speed of 70 km/h)

A walking mynah ©Bhavana Sivayokan 

This covers the basic aspects of the locomotion of birds (birds flying) and some aspects of mechanisms of flight of birds.

The next article will describe the feeding behaviour of birds. 

Click here to read about Fascinating flight of birds

Click here to read about vocalisations of birds

Click here to read about the breeding of birds