Birds of The Kruger and How They Fly
As you drive through the Kruger some of the most common birds you'll see will be Hornbills and especially the Southern Yellow-billed Hornbill. The other 2 common species are the African Grey Hornbill and the Red-billed Hornbill Seeing so many on my recent trip and noting their flight patterns it got me thinking about how birds fly in general.
One of the disconcerting habits of these birds and especially the yellow is to sit on the road until the very last moment before flying off. This means you'll find yourself braking quite a lot. They are also an easy bird to photograph and make excellent subjects given their penetrating glare, multi colour and patterned plumage as well as over-large bills.
A couple of things are really interesting about these birds. The first is the way they fly. Hornbills fly in an undulating kind of way whereby they intersperse flapping of wings with gliding. This is a flight style common to many birds and is designed to save energy. At faster flying speeds the hornbill can also adopt a bounding type of flight whereby it intermittently flaps and closes its wings to "dive" as it were before flapping again to regain height.
But by far the most fascinating characteristic of all African Hornbills is their nesting behaviour and I've created a separate page about this.
Most of the action you will see in the Kruger will revolve around the bird life which is magnificently varied, colourful, and noisy. Next time you visit the Kruger take a bit of time to have a closer look at the birds and their general behaviour.
This short guide to bird flight might help you get a bit more enjoyment out of observing these masters of flight.
Basic Facts Of Flight
A bird will move upwards if the lifting force upwards is greater than the weight of the bird. The bird will move forward if the thrusting forces is larger than the drag or air resistance force. The bird will move up and forward if both these requirements are met. Birds are generally light in weight compared to volume and they have feathers which are very light skeletal structures in their simplest form. The Common Ostrich doesn't fly because its weight to volume ratio is far too high.
In an aeroplane aviation fuel burned in the presence of large amounts of air (oxygen) provide the energy behind the creation of these forces. For a bird an uncanny ability to breathe and hold large amounts of oxygen in its lungs is the basic powerhouse behind creating the necessary forces.
Flapping of a bird's wings allows a forward thrust to be maintained as well as lift. The lift is created by the aerodynamic shape of the wing itself (similar to an aeroplane) ... concave below and convex above. This aerofoil shape allows a relative difference in air speed between air moving over the wing top compared to air moving under the wing.
This difference means the air pressure below the wing is higher than that above the wing and the result is an upward pressure on the wing which at a specific speed and weight combination cause the bird to fly upwards.
The flapping of wings downwards forces air backwards and upward flapping (feathers actually open up) is to reposition the wing for another downbeat without creating too much of a drag. Birds can flap their wings backwards in some instances and this helps landing to take place smoothly for larger birds.
Wing flapping is a noisy business except for Owls...
How do these birds fly so silently? I don't profess to fully understand why but this is the generally accepted explanation ... apparently the leading edge of the many owl’s primary flight feathers are covered with soft barbs which have the effect of silencing the air flow at this point (moving air makes a noise, try whistling) thereby allowing the owl to fly silently.
Just north of Johannesburg is a bird demonstration facility and they have a few tame owls that they get to fly close to people in the audience. The flight is truly amazing to watch at close quarters and completely silent. Consider how amazing evolution is: Pel's Fishing-Owl does not fly silently and does not have these barbs on the leading edge of the wings ... quite simply because fish do not hear aerial noise so the Owl had evolved without this "improvement".
Gliding by birds is a way of covering distance while saving significant amounts of energy. To be a successful glider a bird needs specially designed wings similar to those you see on sea birds, especially Albatrosses, where wings are slender and long and pointed (think of a normal airplane glider).
Soaring as Vultures and many other larger raptors do so well is the result of having very broad wings with "fingers" at the ends (the fingers act as mini individual wings for making fine flight adjustments). Click this small image to enlarge and see what mean.
The large surface area of the wings combined with aerofoil design allows lift to take place more easily than if the wing was narrow (ie limited surface area on which the differential pressure can act ... pressure multiplied by area = force and it is force that lifts the bird).
In strong thermal conditions soaring birds can reach great heights quickly.
You may have noticed in the Kruger that you tend to see more Vultures and Marabou Storks perched on trees on cloudy days or earlier in the morning. The reason is that the birds are waiting for thermals to develop and on cloudy days or in lower morning temperatures there is less of an opportunity for a thermal to form since they depend upon high ground temperatures being created as a precursor to the thermal forming.
A thermal is effectively a warm air current. As air warms its density becomes less and it will tend to rise buoyed up by colder air surrounding the thermal. Hovering is made possible by a manipulation of the wing-beat on the upstroke. This method is very energy intensive and is only successfully applied for any length of time by those birds specifically equipped to do this ... good examples are sunbirds and hawks.
Masters of this technique are Pied Kingfishers. In the Kruger you'll have the very great pleasure of seeing these birds fish if you stay awhile close to rivers that have still pools or slow moving river edges.
That much loved bird in the USA the Hummingbird (attracted by the colour red) is able to move both backwards and forwards while hovering. All hovering birds are helped enormously by headwinds ... i.e. the bird will favour hovering against a breeze blowing directly at it. You can probably use this observation as a means of detecting wind direction although I haven't done any studies on it.
Some birds e.g. swifts fly almost full time and are well designed to conserve energy while flying with great maneuverability.
The reason swifts fly continuously is the result of under-developed feet and on those few occasions when they do land they have to cling to the landing surface.
The tails of swifts and swallows and other birds with "v" shaped tails is to create an ability to maneuver at high speed by changing the shape of the tail in flight.
The Fork-tailed Drongo is an example of a very acrobatic bird whose feats are made possible by its forked tail design. It is also a very common bird in the Kruger and easy to spot being all black virtually and its very obviously broad and forked tail. And of course we've all seen those amazing acrobatics of high speed flying done by swallows and swifts.
Talking about tail shapes my favourite eagle, the Bateleur Eagle , has a very short square-shaped tail which makes it the easiest eagle to identify while in flight. This small tail allows it to maneuver in very tight spaces e.g. in between branches of trees or tight spots. Other birds with such tails are Spine-Tails.
Many birds mix flapping with wing beating in order to cover distance using the minimum amount of energy. This is mainly practiced by small birds which seem to follow an "S" type curve in flight. If you look closely you'll see that some birds actually close their wings on the downward path of the "S". Wagtails in your garden do this. Flocking birds ... on one of my recent trips to Kruger I was able to watch a very large flock of Wattled Starlings. The flock would all fly down to the water's edge to drink and then all fly back to a nearby dead tree to perch for a while. What amazed me is that every time this was done there were no casualties from in-flight collisions or branch collisions either and that every bird managed to get its space on the dead branches. I have no idea how the birds avoid each other flying in such close proximity and in such large numbers at such high speeds but they do it and very successfully too.
Feathers are essential to a bird flying but they are also responsible for the wonderful colours you see in the Kruger's birdlife.
Information obtained from www.thekruger.com