The behaviour of laying hens in aviary systems (a literature review)

Aviaries for laying hens have been developed as alternative systems to conventional battery cages. Aviaries provide certain environmental structures and conditions, such as nest boxes, litter, perches and free space, which are considered desirable with regard to the bird's welfare. The technical development of aviaries has been accompanied by extensive behavioural studies, which showed that the space which is available on several tiers or platforms was widely used for locomotor activity. This results in higher strength of the leg and wing bones. But the risk of bone breakage is also increased by the more intensive movements in avaries. Special care has to be taken to keep optimal distances between perches in both, horizontal and vertical direction. The degree of utilization of the different tiers varies largely during daytime, while a high preference for the upper tiers is observed during night. Foot lesions and keel bone deformation may be caused by the use of perches. Therefore perches must be designed in such as way that they remain dean and dry. Habituation to perches of the young birds enhances the access to feeding and resting areas and nest boxes in the upper tiers. The number of dirty eggs is correlated with the time the hens spend inside the nest boxes. Therefore the access to the nests should only be allowed during the time of day when egg deposition occurs. The type of floor is an important factor for the choice and acceptance of the nest boxes. Floors with mouldable materials or preformed in the shape of the hens body are highly attractive. If litter is provided it is used extensively for pecking, scratching and dust-bathing. There is a high individual variation in the utilization of the litter area among hens. The time spent in the litter also differs in response to the type of aviary system. Restricted access to the litter area reduces the number of floor eggs and dirty eggs. The risk of cannibalism is generally higher in aviaries as compared to conventional battery cages.