BATTERY hens are on their way out in Europe. The European Union has decreed that overcrowded wire cages in which the birds are kept are inhumane, and must go by 2012. But now it seems that the large, open pens which will replace the cages may create problems of their own.
Ralph Freire of Purdue University in West Lafayette, Indiana, says chicks raised in open pens can鈥檛 break away from their mothers, and so fail to learn how to space themselves out. As a result they crowd together, which can lead to aggressive behaviour, malnutrition and sometimes suffocation.
Chicks first leave their mother鈥檚 side when they are 11 days old, says Freire. A chick might only venture as far as to stand behind a rock or clump of grass, but Freire says that being out of sight of the mother seems to play a critical role in developing a sense of space. Birds older than 11 days are much more adept at spatial tasks, he says.
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Under the new EU directive, a maximum of nine birds can be raised per square metre. But if the chicks aren鈥檛 given the opportunity to hide from their mothers or each other when very young, they may never learn to make full use of the pen.
To demonstrate this, Freire raised a number of newborn chicks to treat a tennis ball as a surrogate mother. He then placed some of these 鈥渋mprinted鈥� chicks in pens where they could move away from their 鈥渕other鈥� and go behind a barrier, while others were confined to a bare cage with their ball.
At 13 days old, he tested each chick鈥檚 spatial sense by placing its ball behind one of two screens and letting the chick look for it. All the birds raised in cages with barriers looked behind at least one of the screens. But birds that were raised in bare cages didn鈥檛 even attempt to find the ball. Freire says this could explain the crowding behaviour seen in such birds.
Freire鈥檚 other experiments support the theory. He placed the ball between two obstacles behind a clear screen, which the imprinted chicks had to navigate around to reach their surrogate mother. Though all the chicks eventually made it to the ball, those reared in bare cages made many more errors on the way, he told the annual meeting of the Animal Behavior Society in Bloomington, Indiana last month.
Ethologist Linda Keeling of the Swedish University of Agricultural Sciences in Skara has also shown that chickens find it difficult to perch if they don鈥檛 learn the skill when young. 鈥淚f they don鈥檛 get experience moving in three dimensions early on, they are always worse at it later,鈥� she says.
Freire and Keeling say their findings could improve the future welfare of farmed chickens. 鈥淭he answer might be to rear them in more complex environments rather than open pens,鈥� says Freire. 鈥淲hen they move to open pens as adults they may be able to cope better with the new situation.鈥�