Abnormal behavior of birds in captivity has been found to occur among both domesticated and wild birds. Abnormal behavior can be defined in several ways. Statistically, 'abnormal' is when the occurrence, frequency or intensity of a behaviour varies significantly, either more or less, from the normal value. This means that theoretically, almost any behaviour could become 'abnormal' in an individual. Less formally, 'abnormal' includes any activity judged to be outside the normal behaviour pattern for captive birds of that particular class or age. For example, running rather than flying may be a normal behaviour and regularly observed in one species, however, in another species it might be normal but may become 'abnormal' if it occurs frequently, or in another species it is rarely observed and any incidence is considered 'abnormal'. This article does not include 'one-off' behaviours performed by individual birds that might be considered abnormal for that individual, unless these are performed repeatedly by other individuals in the species and are recognised as part of the ethogram of that species.
Most abnormal behaviours can be categorised collectively (e.g., eliminative, ingestive, stereotypies), however, many abnormal behaviours fall debatably into several of these categories and categorisation is therefore not attempted in this article. Abnormal behaviours here are considered to be related to captive housing but may also be due to medical conditions. The article does not include behaviours in birds that are genetically modified to express abnormal behaviour.
Behaviors When housed under captive or commercial conditions, birds often show a range of abnormal behaviours. These are often self-injurious or harmful to other individuals, and can include feather and toe pecking, cannibalism, stereotypy, vent pecking, as well as abnormal sexual behaviours such as chronic egg laying.
Feather and toe pecking
Feather pecking is an abnormal behaviour observed in birds in captivity (primarily in laying hens) whereby one bird repeatedly pecks the feathers of another. Toe pecking is a similar occurrence in commercialized hens which includes repeatedly pecking the toes of another. Each of these behaviours have been tied to physiological stress (i.e., extremely enlarged adrenal glands) likely caused by housing conditions in captivity.Huber-Eicher, B. and Sebo, F., (2001). The prevalence of feather pecking and development in commercial flocks of laying hens. Applied Animal Behaviour Science, 74: 223–231Sherwin, C.M., Richards, G.J and Nicol, C.J., (2010). A comparison of the welfare of layer hens in four housing systems in the UK. British Poultry Science, 51(4): 488-499
Cannibalism
Cannibalism in birds of captivity is a behaviour often linked to feather pecking. With increasing frequency and intensity of feather pecking, the risk and prevalence of cannibalism increases. Since feather pecking leads to increased food consumption due to heat loss through the skin of the bird, and feather pecking is an already aggressive behaviour that consists of cannibalistic qualities, cannibalism is a common consequential effect. Cannibalism is defined as the act of consuming all or part of another individual of the same species as food.Savory, J., (2010). Nutrition, feeding and drinking behaviour, and welfare. In The Welfare of Domestic Fowl and Other Captive Birds, I.J.H. Duncan and P. Hawkins (Eds). Springer. pp. 165-188Savory, C.J., (1995). Feather pecking and cannibalism. World's Poultry Science Journal, 51: 215–219Rodenburg, T.B., Komen, H., Ellen, E.D., Uitdehaag, K.A., and van Arendonk, J.A.M., (2008). Selection method and early-life history affect behavioural development, feather pecking and cannibalism in laying hens: A review. Applied Animal Behaviour Science, 110: 217-228
Stereotypy
Stereotypies are invariant, repetitive behaviour patterns with no blatant function or objective, and seem to be restricted to captive and/or mentally-impaired animals. Stereotypies are the result of inability of an animal to perform a normal behaviour due to external environmental conditions or circumstance. A common stereotypy in laying hens is pacing which involves the animal constantly walking back and forth in a seemingly ritualistic manner due to no access to a suitable nest site. The pacing stereotypy is also hypothesized to arise from intentional movements of escape, specifically in captive animals such as birds. The overabundance as well as lack of stimulation associated with the sub-optimal environment of captivity are the common factors amongst development of stereotypy behaviours in birds.
Vent pecking
Vent pecking is an abnormal behaviour observed in birds in captivity that involves pecking and causing damage to the cloaca, its surrounding skin, and underlying tissue of another bird. Occurrence of vent pecking is primarily immediately after a bird has oviposited when the cloaca is red and enlarged. Vent pecking, like feather pecking, is a gateway behaviour to cannibalism due to its cannibalistic features of hostility towards another individual that involves the aggressive tearing and damaging of the skin and tissue. Vent cannibalism was found to be the most common type of cannibalism causing death in necropsy results of laying hens.Sherwin, C.M., (2010). The welfare and ethical assessment of housing for egg production. In The Welfare of Domestic Fowl and Other Captive Birds, I.J.H. Duncan and P. Hawkins (eds), Springer, pp. 237-258Potzsch, C.J., Lewis, K., Nicol, C.J. and Green, L.E., (2001). A cross-sectional study of the prevalence of vent pecking in laying hens in alternative systems and its associations with feather pecking, management and disease. Applied Animal Behaviour Science, 74: 259-272
Additional behaviors Toe peckingLeonard, M.L., Horn, A.G. and Fairful, R.W., (1995). Correlates and consequences of allopecking in White Leghorn chickens. Applied Animal Behaviour Science, 43: 17-26Buitenhuis, A.J., Rodenburg, T.B., Siwek, M., Cornelissen, S.J.B., Nieuwland, M.G.B., Crooijmans, R.P.M.A., Groenen, M.A.M., Koene, P., Bovenhuis, H., and van der Poel, J.J., (2003). Identification of quantitative trait loci for receiving pecks in young and adult laying hens. Poultry Science, 82: 1661-1667 Feather plucking StereotypiesSargent, T.D. and Keiper, R.R., (1967). Stereotypies in caged canaries. Animal Behaviour, 15: 62-66 PolydipsiaHardy, W.T. and Westbrook R.F., (1981). Lithium-induced polydipsia in birds: A comparative study and analysis of electrolyte excretion. Physiology and Behavior, 27: 575-583 Sham or "vacuum" dustbathingOlsson, I.A.S., Keeling L.J. and Duncan, I.J.H., (2002). Why do hens sham dustbathe when they have litter? Applied Animal Behaviour Science, 76: 53–64Merrill, R.J.N., Cooper, J.J., Albentosa M.J. and Nicol, C.J., (2006). The preferences of laying hens for perforated Astroturf over conventional wire as a dustbathing substrate in furnished cages. Animal Welfare, 15:173–178van Liere, D.W., (1992). The significance of fowls' bathing in dust. Animal Welfare, 1: 187–202 Jealous, over-possessive parrot Chronic egg laying Infertility Abnormal biting
Causes When analyzing the behaviour of birds in captivity, what is considered normal or abnormal behaviour is dependent on the form and frequency that the particular behaviour is expressed in the natural environment.Wiepkema, P.R. (1985). Abnormal behavior in farm animals: ethological implications. Netherlands Journal of Zoology, 35, 279-299. Birds raised in pet stores tend to be raised with other birds, however, after being sold and taken to the owner's home, birds in captivity are often housed in isolation and in environments lacking abundant resources or complex stimuli. In the United States, it is estimated that forty million birds are kept caged and improperly cared for. Because of these inappropriate housing conditions, abnormal behaviour patterns may appear in caged birds kept as pets. Once established, these abnormal behaviours in birds are often not alterable.Ten Cate, C. (1995). Behavioral development in birds and the implications of imprinting and song learning for captive propagation. Research and Captive Propagation, 187-197.
When social interactions amongst birds are absent or inadequate, abnormal social behaviour may develop. For example, a study regarding parrots that had been isolated in cages demonstrated that most birds showing this social deprivation had significant behavioural disturbances, such as aggressive behaviour, feather picking, self-mutilation, restlessness, screaming, apathetic behavior, and stereotypies.Lantermann, W. (1993). Social deprivation in Amazon parrots. Animal Behaviour, 38, 511-520. Several parrots living in captivity monitored during a study have displayed behaviors consisting of screaming excessively and biting. This specific noise made by these birds is encouraged in captivity. Biting however is not a typical defense mechanism used by wild parrots. Cannibalism often occurs in large animal husbandry systems, which are usually impoverished environments with a lack of opportunities.Hughes, B.O. & Duncan, I.J.H. (1998). The notion of ethological "need," models of motivation and animal welfare. Animal Behaviour, 36, 1696-1707. In addition, studies of caged canaries have revealed two common stereotypies. These include spot picking, where birds repeatedly touch a particular spot in the environment with the tip of their beak, and route tracing, a pacing behaviour associated with physical restrictions in movement imposed by the cage. The absence of song learning in zebra finches has also been implicated as a behavioural abnormality.Slater, P.J, B., Jones, A. & Ten Cate, C. (1993). Can lack of experience delay the end of the sensitive phase for song learning? Netherlands Journal of Zoology, 43, 80-90. In these birds, the social interaction of a young male with his song tutor is important for normal song development. Without the stimulus, the song, which is necessary for mating behavior, will not be learned.
Researchers have analyzed ways to alleviate some abnormal behaviours in caged birds. Presenting these birds with novel stimuli e.g. a mirror or plastic birds, and social stimuli, such as a brief view of a bird in another cage, significantly reduced stereotypies.Keiper, R.R. (1970). Studies of stereotypy function in the canary (Serinus canarius). Animal Behaviour, 18, 353-357. In addition, it has been suggested that keeping caged birds in pairs or small groups may reduce the development of abnormal behaviours, however, little quantitative evidence has thus far been collected to support this claim.
Statistically, 1/10 of endangered birds tend to have egg infertility, but this number increases for breeders of endangered species working with captive birds.