We all know there are myriad reasons why the chicken crossed the road, but have you ever wondered how it got to the other side?
The answer is unlikely to be ‘by flying’.
The domestic chicken (Gallus gallus domesticus) is the most populous bird in the world. Over 34 billion chickens are kept for their eggs and meat production, and although the vast majority of those are reared indoors where they have little chance of ever flying, a good proportion are kept outdoors on free range farms, smallholdings, and in people’s gardens.
Despite this, it would be highly unusual to hear of a chicken doing a runner by flying away in the same way that we might be aware of other domesticated and pet birds escaping into the wild.
The domestic chicken is descended from the red junglefowl (Gallus gallus), a tropical bird from Southeast Asia. It belongs to the Phasianidae family which also includes pheasants, partridges, quails, and peafowls. Since the original domestication, chickens have also been partially hybridised with the other extant species of junglefowl – the grey junglefowl, the Ceylon junglefowl, and the green junglefowl – to give the wide variety of breeds we have today.
Like other members of its family, the red junglefowl is able to fly but only for short distances. It spends most of the day on the ground searching for fallen fruits and seeds, and will only take off into the air to reach its roost at sunset or to escape a predator or other immediate danger.
So why, you might ask, don’t domestic chickens use that ability to fly when, for example, a fox comes near?
Like other game birds, junglefowl and chickens have big flight muscles that are optimised for taking off vertically and short bursts of horizontal flight, but because they use them much less frequently than other flying birds, they contain less myoglobin, a protein that provides muscles with the oxygen needed for movement. Myoglobin is also responsible for giving meat its red colour which is why the breast meat on game birds and chickens is white, and preferred by meat-loving consumers, and leg and thigh meat, which game birds use to get around, is darker.
It may seem counterintuitive that large flight muscles mean less flight, but for birds to be able to fly depends on what is called ‘wing loading’ or the ratio of body mass to wing area. The larger the wings compared to the weight of the bird, the better it will be able to fly. As game birds tend to have short wings with a small surface area, the heavy flight muscles actually impede their ability to fly.
In the 6-8,000 years that chickens have been domesticated, to optimise white meat production, breeders have selected traits that have increased the size of the flight muscles even more than that of their wild ancestor. They have also increased the size of the thighs so that most domesticated chickens are simply far too heavy to get airborne.
Some of the smaller breeds such as Araucanas , Anconas, Jaerhon Leghorns, Spitzhaubens, Rhode Island Whites, and Red Rangers, as well as bantams can fly, but only for short distances, while young chickens who have not yet put on weight might have a go at flapping their wings and taking off.
According to Guinness World Records, the longest poultry flight was achieved by Sheena, a barnyard bantam kept Bill and Bob Knox in Parkesburg, Pennsylvania, who managed a flight of 192.07 m in May 1985.
Even if domesticated chickens could fly as well as the junglefowl, the manner in which they fly means that if they are close to a high enough fence, they wouldn’t be able to take off at a steep enough angle to get over it. And if they were far enough away where they could take off at a lower angle, they wouldn’t be able to fly for a long enough distance to clear it. This means that most domestic chickens can be kept quite safely in a pen with no need for a roof.
However, to be sure that chickens don’t escape or end up somewhere they shouldn’t, many owners choose to clip their chickens’ wings. This is a harmless practice where about half of the primary feathers on the wings are cut to prevent the chicken flying away.
