The domesticated chicken is a descendant of the Red Junglefowl of Southeast Asia. Red junglefowl habitat stretches from north-eastern India to the Philippines. They browse on the forest floor for insects, seeds and fruit, and fly up to nest in the trees at night. They live in mixed-sex flocks and have a distinct hierarchy – a pecking order.
The basic behavioural repertoire of domestic chickens is fundamentally the same as that of their wild ancestors. They are generally crepuscular; active early in the morning, with a rest during the day, and awake again from late afternoon until dusk. At dawn, the roosters, start the day by crowing loudly, reinforcing territorial boundaries and dominance relationships. They spend a great part of their day foraging, walking, and pecking at the ground.
Hens possess complex emotional capacities and cognitive abilities, and they demonstrate sophisticated communication skills which have evolved over millions of years to help them to share information and protect each other from harm.
Hens are social creatures and they live in complex societies. They establish stable social hierarchies, with each individual hen being able to recognise every other individual hen within their flock and to understand the relative social status of each individual bird within the flock.
Hens develop individual friendships with their flock mates and show a preference to spend time foraging, sleeping and preening with these friends. They will often stay close together and synchronise their foraging and preening activities, and they maintain contact with a ‘Ku’ call and warn each other about potential dangers.
Hens are believed to have over 30 different vocal calls and use these to exchange information and to indicate their emotional state. Hens have contact calls; laying and nesting calls; mating calls; threat calls; submissive calls; distress, fear and alarm calls; contentment calls; food calls, and warning calls.
Hens have been observed responding to calls indicating the presence of novel food but not so much to food calls about known food. Thus, it appears that the cognitive processes involved in representational thinking in chickens are like those required for associative learning in humans.
Hens have distinct alarm calls for aerial or ground predators, which other hens respond to appropriately by standing up alert, crouching or taking cover, and males are more likely to give alarm calls when there are females nearby. The cockerels will also crow to advertise their territory and to assess other male within the flock.
Hens also communicate by postures and visual displays (for example to signal threat or submission). Bodily features such as comb size and colour are used as signals of sexual or social status, and for recognising each other.
Hens have a ‘frustration’ call (the gakel) when they are thwarted in getting to food, water, a dust bath or a nest box. When hens were trained to expect food in a situation and then food was withheld, the hens with the highest expectations showed most frustration.
Hens are also known to develop specific calls which identify their human carers to each other. This behaviour has previously been documented in prairie dogs and gregarious ground squirrels, using specific sounds to communicate to others that a human has been spotted and describing the human to others within their group.
If a male finds food, he will call and perform a series of movements and any other hen seeing this will say ‘Aha’, that guy has got food, and come rushing over. This shows the group that he has a competitive advantage over his potential rivals and in doing so he increases his changes of attracting a mate. Males enticing females with food is a form of courtship, but it does not necessarily lead to immediate mating. The females take their time to evaluate the males’ behavior, and so form an opinion about various males — and their reputations for providing food — and then commit these various experiences to memory. Only then does the female express a mating preference.
Submissive males within a flock will also use clever and deceptive strategies to court females while diverting attention away from the dominant male who would otherwise derail their plans. Their objective is to outsmart the dominant male by attracting a potential mate away from him without him getting wise to the submissive male’s intentions. And this strategy often succeeds.
Communication between the mother hen and her chicks is also vital, and this communication begins before the chicks even hatch out of their eggs. Chicks inside the egg emit a distress call, when cold, for example, and the hen responds to such calls by moving the egg in the nest, to a warmer position. The developing chicks also emit pleasure calls when their mother hen responds.
This sophisticated communication is not limited to the hen and her chicks, as nest mates also influence each other with their vocalizations. Clicking and bill clapping sounds made during late development are thought to help synchronize hatching, so that all the chicks in a clutch break free of their shells at approximately the same time.
The communication abilities of hens are thus highly complex and allows them to live and prosper within the world that they have evolved to live within.
It turns out that hens really are amazing animals
The welfare of hens raised for food
Approximately 58 billion chickens are slaughtered for meat annually; over 70% are raised via intensive systems . Chicken meat is one of the cheapest meats available; this is due to intensification which has allowed farmers to mass produce meat chickens by increasing the growth rate and stocking densities to produce more chickens at a faster rate. The essential step in turning the traditional farmyard chicken into a manufactured item was confining them indoors.
Intensively reared meat chickens otherwise known as broiler chickens are hatched, de-beaked to reduce injuries and death from fighting and placed in large often windowless barns. Inside these barns every aspect of the birds’ environment is controlled to make them grow faster on less feed. As a result of selective breeding most broiler chickens grow to a slaughter weight of over 2kg within 6 to 7 weeks, this is a reduction in time by 50% on traditional practices, free-range chickens are usually slaughtered at 8 weeks and organically reared chickens at 12 weeks. . In 1920, a chicken reached 1kg in 16 weeks, but broiler chicken strains may now reach 2.27kg in only 7 weeks.
As a result of selective breeding and higher stocking densities, broiler chickens suffer from a variety of welfare problems:
The poultry industry places great demands on the birds’ musculoskeletal system in terms of growth rates for broilers. Any insufficiencies in the birds’ nutrition or management will often lead to musculoskeletal diseases, which are normally characterized and diagnosed by lameness. Lameness will cause birds to suffer and limit their natural movements, likely resulting in reduced feed and water intake. Leg disorders and lameness adversely affect the performance and wellbeing of poultry while increasing morbidity and mortality.
The intense selection of broiler chickens for fast growth rate and a high meat yield puts pressure on the bird’s heart and lungs. In the UK alone, millions of chickens die in their barns from heart failure each year. The main heart problems are ascites and sudden-death-syndrome.
Broiler ascites syndrome is a metabolic syndrome resulting from an imbalance between oxygen requirement and oxygen supply. Symptoms displayed by the chickens affected with this syndrome include dullness and depression, an irregular heartbeat, open beak breathing, a distended abdomen and reluctance to move. The syndrome usually results in heart failure and death late in the rearing period or even during transport to the slaughterhouse.
Sudden death syndrome is a condition in which fast growing broiler chicks die suddenly with no apparent causes. It has developed into a major problem for the broiler industry in many parts of the world. Broiler chickens of all ages are affected starting as early as 2 days of age and continues up to marketable age. Peak mortality usually occurs between the 3rd and 4th week with more affect being observed in male birds than the females. There is usually a short wing beating, convulsions prior to death. Most affected broilers are found dead lying on their backs. Lung oedema is a prominent post-mortem lesion. The condition is undoubtedly related to fast growth rate and as such management techniques to reduce the early maximum genetic potential for growth offer the best preventive scenario.
Due to lameness and overcrowding, many broilers spend a disproportionate amount of time squatting on the litter (usually wood shavings) which covers the floor. All too often it is damp and dirty. Prolonged contact with such litter leads to many birds suffering from painful breast blisters, hock burns and ulcerated feet. As well as being painful, these injuries allow infections to enter the bird; these can spread through the bloodstream causing joint inflammations.
Poultry manure and its nitrogenous compounds cause eutrophication, nitrate or nitrite contamination of water, ammonia volatilisation and acid deposition in the air. Ammonia gas results from the chemical decomposition of uric acid in droppings by bacteria in the litter. Ammonia gas has a pungent odour. At high concentrations it is irritating to mucous membranes of the respiratory tract and the conjunctivae and corneas of the eyes. Damage to the mucous membranes of the respiratory system increases the susceptibility of birds to bacterial respiratory infection, especially E.coli infection.
The welfare of hens raised for egg production
There are an estimated 6.6 billion egg laying hens globally.
It is estimated that more than 60 percent of the world’s eggs are produced in industrial systems, mostly using barren battery cages. These cages are so small hens cannot stretch their wings and are prevented from carrying out other natural behaviours such as laying eggs in a nest, pecking and scratching the ground, dust-bathing and perching.
Hens are often crammed inside cages with 4 and sometimes 5 birds, and feather loss is high as birds redirect their natural pecking behaviour towards each other, pulling out other birds feathers and preventing natural feather re-growth. This occurs even after the chicks have been debeaked. For commercial laying hens, chicks are trimmed manually, either at day old or up to 7 days of age using a hot blade to remove and cauterise the tip of the beak. The accepted procedure is to remove not more than one third of the upper and lower beaks or not more than one third of the upper beak only.
Since the beak is a sensory organ and a primary means by which a bird interacts with its environment, beak trimming may affect its ability to express normal behaviour while the act of beak trimming itself causes pain, suffering and distress. Debeaking is thus a mutilation addressing the symptoms of overcrowding rather than the causes of feather pecking.
The exact causes of feather pecking are not known, but may include redirection of foraging behaviour, genetic predisposition, plumage colour variation in target animals, light intensity, food access and composition, perch access, drinker type, use of litter, and stocking density.
The restriction of natural behaviours is one of the greatest welfare concerns. Research has shown that hens have a strong preference for laying their eggs in a nest and are highly motivated to perform nesting behaviour. Hens also show a strong preference for a littered floor both for pecking and scratching and for dust-bathing, and a preference to perch, especially at night. Conventional ‘battery’ cages prevent the birds performing these natural behaviours.
Hens in conventional ‘battery’ cages often develop severe foot injuries due to the wire flooring. Due to the lack of a suitable substrate hen's claws often become overgrown and can become wrapped around the wire flooring preventing movement.
The laying hen industry also has no place for ‘male chicks’ and therefore they are considered as an unwanted by product of egg production and millions of male chicks are either gassed or crushed at one day old, the crushing is known as maceration. In the EU alone an estimated 330 million-day old chicks are slaughtered annually.