A study in California found that duck hunters using spinners killed six times as many birds in the early season, four times as many birds in the middle of the season and twice as many birds in the late season as hunters without spinners. A check-station survey found that hunters using motorized decoys killed 56 percent more birds than hunters who didn't use them. Crippling rates there did not go down when spinners were being used.

The effectiveness of the spinning-wing decoy has waterfowl biologists wondering about several management issues.

First, is this new technology reducing duck numbers on any flyways? We have a better picture of North American duck populations and their trends than we do for any other group of widely distributed wildlife. Still, the forces that affect duck numbers are complicated and difficult to track. It's nearly impossible to figure out how a change in hunting technology affects duck numbers continent wide. So far, there is no evidence that spinners are reducing duck numbers on a wide scale.

Second, is this technology a special threat to particular species or local populations of ducks? For California biologists, the high rate of mallard harvest over spinners early in the season was a danger signal. They were afraid that local mallard populations might suffer unless early-season use of spinners was restricted. This may be an important consideration in any area that combines heavy hunting pressure with important local birds. So far, there is no research on the effect spinning-wing decoys might have on species like black duck and pintail.

Third, is this technology changing the distribution of duck harvests? Harvest statistics haven't shown a sudden spike since the advent of spinning-wing decoys, so they may have no effect on overall harvest. Several studies show that spinners are effective on adult ducks and continue to be effective down the flyway, suggesting that they aren't likely to give northern hunters a new advantage. However, it's clear that hunters with spinners take more ducks than hunters without.

Four states -- Pennsylvania, Oregon, Washington and Arkansas -- have already banned motorized decoys, or some form of decoy that spins or flaps their wings or vibrate in the water. California and Minnesota have banned motorized decoys in the early part of the season, and the U.S. Fish and Wildlife Service has been encouraging discussion, trying to decide whether federal regulation might be in order.

Over the last century, ethics have repeatedly made their way into the laws that govern waterfowling. If maintaining populations of ducks is our only concern, we can do it with little more than a well-enforced bag limit and a season of the right length. The laws against live decoys, baiting, sink boxes, punt guns, shooting after dark, hunting from boats under power or sail, loading more than three shells and using recorded calls have more to do with ethics than managing waterfowl. At some point, we decided that certain ways of killing birds wandered over the line separating sport from slaughter.

The man who taught me how to hunt said that an ethical hunter never takes advantage of his quarry -- he gives advantage. When our best effort never succeeds, we probably have room to look for more efficient techniques. When we never fail, we should consider ways to limit ourselves. That's the balance that makes fair chase fair.