Is there anything as awe-inspiring as a bird in flight? Whether it’s watching the speed and accuracy of a Little Bee-eater hunting on the wing at Umusambi Village or the sight of African Fish Eagles soaring above the lakes of Akagera National Park. I can’t be the only one to wonder what it would be like to fly like a bird? ALSO READ: The birds that call Rwanda home Unfortunately, even if we had extremely large wings we wouldn’t be able to – we are simply too heavy and too clumsy! From studying fossilised remains – some dating back millions of years - we know that much of the evolution of birds has been shaped by the requirements of flight. Heavy jaws and teeth are gone, in their place are lightweight bills. Hollow bones, supported by internal struts make them lighter for flight. Internal organs and muscles are concentrated in a compact central mass. ALSO READ: Birds of Rwanda: Dressed to impress! Moreover, the internal organs used for breeding only grow for their breeding season, afterwards they decrease in size again. Laying an egg is another advantage for flight. Unlike mammals, such as us humans, who spend months carrying their young inside their bodies as they grow, a female bird is able to fly while her offspring develops in the nest. How birds breathe has also evolved. Like us humans, birds breathe in and use oxygen and then breathe out carbon dioxide. However, birds have air sacs as well as lungs. ALSO READ: Saving Rwanda’s grey-crowned cranes Their one-way system means that incoming oxygen is not contaminated by outgoing carbon dioxide. This in turn means one bird breath goes further and does more work than one human breath. It also means that birds have a constant supply of fresh air in their lungs – which they need to fly, especially if migrating long distances or flying at high altitudes. Another and probably the most obvious way birds have evolved for flight is the feather. Made of keratin - just like our fingernails - they cover the bird’s body. The different types of feather enable them to fly, help reduce turbulence when flying, keep them warm and insulated when they fly at high altitudes, as well as shielding them from wind and rain. Taking off requires maximum energy and an explosion of effort, just watch a Spur-winged Goose try and take off from one of the ponds at Nyandungu Eco-Park and you’ll see what I mean! You will see the goose frantically flapping its wings to generate lift whilst at the same time trying to run across the water to build speed – water will be spraying everywhere too! It will eventually leave the water and rapidly gain height; its webbed feet will then be tucked beneath its tail as it flies away. Even the smaller water birds expend lots of energy taking off, have a look at the accompanying image of a Little Grebe! Obviously, not all birds take off from the water, large birds on land are just as elegant as the goose I described - but with a lot less water involved! In contrast, taking off from branches or other perches takes less effort. Birds let gravity pull them downwards so enough speed can be generated and their wings are able to work as aerofoils. It’s the shape of a bird’s wing - when viewed from the front of the bird - that keeps them in the air. This aerofoil shape also helps keep aeroplanes in the sky too! In section, the front edge is thick and rounded which curves slightly downwards and gets thinner towards the back – a feather thick! (think of a comma on its side). As a bird glides forwards with its wings outstretched, air flowing over the top of the wing’s surface is deflected upwards which reduces the air pressure just above. Air flowing under the wing is disturbed by the downward curve of the wing and therefore increases the air pressure below the wing. With less air pressure above and more below, the wing will tend to rise upwards. The width, length and overall design of a bird’s wing is heavily influenced by the feeding behaviours of the different species and also whether they migrate or not. One wing design is short and narrow, which enables these birds to take off rapidly and at a steep angle – two examples seen here in Rwanda include the Yellow-billed Duck and Spur-winged Goose. The next is short and broad, these wings are superbly designed for fast and low flight with explosive take-offs. Most of Rwanda’s smaller resident birds have this shape of wing, including the White-collared Oliveback and the Swamp Flycatcher. Another is long and narrow, this is a high-speed wing design. Great examples which are commonly seen here in Rwanda include the Lesser-striped Swallow and African Palm Swift. The final category of wing design is long and broad, the majority of birds with these wings have ‘fingertips’ at the end of the wing to help reduce turbulence. These birds are great gliders as the wing design generates lots of lift and thrust. The Palm Nut Vulture, Yellow-billed Stork and Grey Crowned Crane are all great examples with this wing type. Whilst the wings are all about generating thrust and lift, the tail is vital for steering and enabling manoeuvrability. In general, the longer and larger the tail, the more stable a bird’s flight will be. Flapping wings uses a lot of energy, so birds have found ways to conserve their energy whilst in flight. One such way used by many species is intermittent flight. This is when phases of flapping are interrupted with fixed-wing pauses. Lots of small to medium birds here in Rwanda utilise this energy-saving form of flight, including the Black-headed Gonolek, Red-eyed Dove and African Grey Woodpecker. Those birds with long and broad wings will use rising air currents for soaring. On warm sunny afternoons in Kigali, large groups of Yellow-billed Kites can be seen riding the warm rising air thermals. Large birds like the Yellow-billed stork will also make use of rising thermals to save energy when migrating or covering long distances in search of food. Just as you will see the cyclists in formation during the ‘Tour du Rwanda’ behind the lead cyclist trying to to make use of the leader’s ‘slipstream’. Pelicans, ducks and geese also do this when flying as a flock. On lakes across Rwanda you will often see groups of birds, like the African Darter, Reed Cormorant and White-faced Whistling Ducks flying low across water and in formation. This is because there is less wind resistance closer to the surface and therefore the birds will use less energy than when they are flying at a higher altitude. -- I find watching Rwanda’s birds in action a great way to relax, next time you have a moment to look and enjoy the spectacle. Even better if you manage to get a photo; tag me @2wsphotography.
