Traffic cones near the Homer Tunnel kept moving. The tunnel is bored through the mountains on the only road into Milford Sound, at the bottom of New Zealand's South Island, and for weeks in 2016 the road crew kept finding its cones where they had not left them. Somebody eventually pulled the tunnel footage. Kea, pronounced KAY-uh, the world's only alpine parrot, had been dragging cones into the live lane, backing off as the cars came, then coming out to move them again.

Kea don't grow out of play. They are still at it as adults, long after their closest relatives have stopped. But cones on the road put the birds on the road, and a highway running through a national park cannot be fenced. Kea are endangered, so a plan was set in place to protect these mischievous feathered roadworkers.

The response was an enrichment gym. The Department of Conservation, a road contractor, the University of Canterbury and the Kea Conservation Trust built the birds a roadside playground: ladders, swings, spinning floats, climbing frames, rearranged every so often. A person is employed to stop the parrots from getting bored. Three more gyms sit at key kea hotspots on the South Island, one at the Manapouri power station, where the birds had been taking cars apart in the parking lot. Kea steal items indiscriminately and rip holes in tents. A kea peeling the rubber trim off a car door gets long satisfying strips and nothing to eat.

Play looks like surplus energy, something young animals do because they have it to burn. Karl Groos, a German philosopher who published The Play of Animals in 1896, read it the other way round: an animal isn't playing because it's young, it's young so that it can play. Childhood is when the kea finds out which things come apart, and which of those are food.

Even a kea slows down. Immature birds approach and handle novel objects far more readily than adults do, and new behaviors enter the flock through the young, adults picking them up by watching juveniles. The flock's supply of new food comes from the members with the least judgment. The food moves every season, mountain daisy roots in spring, rātā and mountain flax nectar in summer, beech buds in autumn. In winter the snow closes the tops and the birds drop below the treeline for carrion and grubs. A bird that only returns to what worked last season eats well until the season stops cooperating.

A kea only slows down. Developmental psychology has long had us done pretending at about six, when school starts. Children's free play has been contracting across the developed world for fifty years, and the hours it lost went to activities with an adult present and a measurable result at the end.

Eighteen years later that child is at a desk when a co-worker picks an outcome, builds an activity backward to reach it, and calls the result play. An offsite with a post-mortem is a meeting held outdoors. A hackathon judged by leadership is a sprint with better snacks. A blue-sky session with a scribe is minutes. Attach a reviewer, make sure the lesson is learned and the value extracted, and none of it was ever play.

Lev Vygotsky, the Soviet psychologist, gave a lecture in Leningrad in 1933 that survives only because a stenographer was in the room. In play, he said, a child is a head taller than himself, above his own daily level. His example was a candy the children weren't allowed to eat under the rules of their game. It went uneaten. No adult could have gotten them to do that. Play keeps asking a child to act against immediate impulse, and a child's self-control is never greater than in play. Nobody set that rule but them.

The objection is budgetary. Nobody has spare hours, and next quarter is already spoken for. Unassigned play hours do come out of the work. They're also the only hours that go looking for what will work next. Delete time for play and nothing shows up in the numbers as bad. Velocity holds and the roadmap ships on time. Both measure how well you're repeating what worked last season. Neither can tell you the food has moved, and nobody is out looking.

Somebody has always paid for the kea's curiosity. The birds do go after sheep, perching on the rump and digging through to the fat around the kidneys, and 150,000 kea were shot between 1860 and 1970, for a government bounty to protect the shepherds' flocks. Bounty hunting was outlawed in 1971 and full protection took until 1986. Somewhere between one and five thousand birds are left.

One behavior, two responses. A price on the bird's head, and a set of swings by the side of a road.

Most companies have a version of the cones, the thing people keep doing that no ticket covers and nobody asked for. Every company has already chosen a bounty or a gym. You can tell which by what happened to the last person who played on company time.