The egg-laying urge and the egg shortage.

One factor precipitating the egg shortage – and there are several – was the activation of legislation at the end of last year to end the use of battery cages in New Zealand. Colony cages were allowed instead because these provide a few basic hen resources that battery cages did not, including a screened area to lay eggs. In coming to this decision, the National Animal Welfare Advisory Committee reviewed scientific research into what hens “need”. Assessing what a need is involves measures of physiology and behaviour.

Two well-known behaviour experiments assessed how important a private nesting spot is to hens by measuring what ordeals they will put themselves through to access such a place when the laying urge strikes. One experiment showed that to get to a nest box, hungry and thirsty hens will push as hard against a heavy door as they can to get food and water. They’ll also push through very narrow gaps – something they generally avoid doing – to get to a nest box, even if they’ve never had the chance to use one before. This extreme motivation to get to something suggests that without it, a need isn’t being met and the animal suffers. In this case it’s only important when the urge to lay is present, of course.

Some chicken keepers might wonder why it’s not blatantly obvious that a hen needing to lay an egg needs a private spot. But regulators need objective evidence to back up their decisions, especially when altered regulations increase costs and involve major change from the status quo.

Similarly, convincing evidence exists for hens’ need to perch and to have something to scratch at. Colony cages therefore contain perches and a knobbled mat over part of the wire-mesh floor – an incredibly poor substitute for what they’d get in an average backyard coop.