How Birds evolved the ability to fly
By zteve t evans
The question of how birds evolved the ability to fly has been an ongoing debate for centuries. To try and answer this question we will first discuss reasons why birds fly. Then we will look at four different theories that have emerged to attempt to explain how birds took to the skies. Finally, we will briefly discuss what, if any, expert consensus there is about how birds evolved the ability to fly
Why Fly?
Powered flight takes up a lot of energy and many large species use air currents and updrafts to glide and soar so they do not have to flap their wings. This is a good way for them to save energy. But if flying takes up so much energy why use it at all?
There are a number of important activities that birds use flight for. Some species of bird use flight to make it easier to find and hunt their prey, or to avoid predators. Others use it for foraging for berries, nuts and other food as they move through the trees. Flight is also useful to travel quickly and safely from one feeding ground to another and to migrate to other locations with the seasons. Some species enact spectacular aerial displays to attract a mate during the breeding season. Flight is also useful when they want to build a nest in a safe place that is as inaccessible as possible to predators. So while flight takes up a lot of energy it gives birds many important advantages, so how did they evolve this amazing ability?
Powered flight takes up a lot of energy and many large species use air currents and updrafts to glide and soar so they do not have to flap their wings. This is a good way for them to save energy. But if flying takes up so much energy why use it at all?
There are a number of important activities that birds use flight for. Some species of bird use flight to make it easier to find and hunt their prey, or to avoid predators. Others use it for foraging for berries, nuts and other food as they move through the trees. Flight is also useful to travel quickly and safely from one feeding ground to another and to migrate to other locations with the seasons. Some species enact spectacular aerial displays to attract a mate during the breeding season. Flight is also useful when they want to build a nest in a safe place that is as inaccessible as possible to predators. So while flight takes up a lot of energy it gives birds many important advantages, so how did they evolve this amazing ability?
From the trees down theory
The arboreal or "from the trees down" theory was one of the first attempts to explain how birds took to the skies. This says that birds leaping from branch to branch and from tree to tree were aided by having feathers on their limbs which aided gliding. Eventually they learnt to glide to a greater distances and to steer themselves achieving more aerial manoeuvrability. Eventually as they evolved the ability to flap their limbs became wings capable of giving them the ability of powered flight.
The cursorial theory
Also known as the "from the ground up", the cursorial theory is the idea that birds learnt to fly by running along the ground with feathered forelimbs outstretched to aid balance and stability. This could have been while chasing prey, trying to escape predators, or it could have been part of a display ritual. The idea is that by running in such a way, possibly aided by a leap, they could have been caught up by wind or air currents and achieved flight for short periods
Wing-assisted incline running
Similar to the cursorial model, this theory says that birds achieved flight by flapping their wings when running up a steep incline such as a slope in the ground, a boulder or cliff, or a tree to escape from predator.
The pouncing proavis theory
The pouncing proavis theory is a more modern idea which proposes that birds evolved the ability of flight from raptorial predecessors. These ancestors were predators who had evolved strong talons or claws and specialised in using ambush attacks from high stations such as cliffs or trees to drop on prey that passed beneath. By stretching out feathered fore limbs they may have learnt how to glide or swoop and to adjust their flight path or to gain greater distance. Unlike the arboreal theory which emphasises flitting or short leaps from branch to branch this places the emphasis on gaining greater swooping distance to catch prey.
No expert consensus
There does not seem to be any clear expert consensus on the theories that have been outlined.
Perhaps different species of birds evolved flight differently depending on their circumstances. Modern research and new fossil finds continue to push back the barriers and give new insights into the question of how birds evolved the ability to fly.
© 05/08/2014 zteve t evans
The arboreal or "from the trees down" theory was one of the first attempts to explain how birds took to the skies. This says that birds leaping from branch to branch and from tree to tree were aided by having feathers on their limbs which aided gliding. Eventually they learnt to glide to a greater distances and to steer themselves achieving more aerial manoeuvrability. Eventually as they evolved the ability to flap their limbs became wings capable of giving them the ability of powered flight.
The cursorial theory
Also known as the "from the ground up", the cursorial theory is the idea that birds learnt to fly by running along the ground with feathered forelimbs outstretched to aid balance and stability. This could have been while chasing prey, trying to escape predators, or it could have been part of a display ritual. The idea is that by running in such a way, possibly aided by a leap, they could have been caught up by wind or air currents and achieved flight for short periods
Wing-assisted incline running
Similar to the cursorial model, this theory says that birds achieved flight by flapping their wings when running up a steep incline such as a slope in the ground, a boulder or cliff, or a tree to escape from predator.
The pouncing proavis theory
The pouncing proavis theory is a more modern idea which proposes that birds evolved the ability of flight from raptorial predecessors. These ancestors were predators who had evolved strong talons or claws and specialised in using ambush attacks from high stations such as cliffs or trees to drop on prey that passed beneath. By stretching out feathered fore limbs they may have learnt how to glide or swoop and to adjust their flight path or to gain greater distance. Unlike the arboreal theory which emphasises flitting or short leaps from branch to branch this places the emphasis on gaining greater swooping distance to catch prey.
No expert consensus
There does not seem to be any clear expert consensus on the theories that have been outlined.
Perhaps different species of birds evolved flight differently depending on their circumstances. Modern research and new fossil finds continue to push back the barriers and give new insights into the question of how birds evolved the ability to fly.
© 05/08/2014 zteve t evans
References and Attributions
Copyright August 8th, 2014 zteve t evans
Copyright August 8th, 2014 zteve t evans