The results? In the marsh, ducks were 1.9 times more likely to fly within 40 yards with the spinner running than when it was off. Hunters killed five times more ducks when the wing-spinner was active. Interestingly, crippling dropped from about 0.3 birds per hunter to about 0.2 birds per hunter when the spinner was on.

The difference was even greater in field hunts: Ducks were five times more likely to fly within 40 yards when the spinner was running, and kill was 33 times higher. During the early season, crippling rates didn't change, but late in the season, crippling was 3.7 times lower when the decoy was running.

The Caswells also sexed, aged and weighed the birds that were killed during the experiment. Other research has suggested that juvenile ducks are more likely to come to decoys than their parents. There is also reason to believe that ducks in poorer condition are more likely to come to decoys than ducks that are well fed. The Caswells found that the spinning-wing decoy changed that pattern -- when it was running, hunters generally killed more adult mallards, and the birds they took were heavier, i.e., better fed.

Of course, Manitoba waterfowlers have the luxury of hunting untutored mallards. If the ducks are learning to avoid spinning-wing decoys, their increasing wariness is likely to be most obvious farther south, but studies down the flyways have seen the same impact.

Researcher Michael Szymanski set up a study in Minnesota similar to the Caswell's -- 367 hunts with two spinners turned on and off at 15-minute intervals. Mallards were 2.9 times more likely to fly within 40 yards when the decoys were running. Flocks responding to the spread were 1.25 times larger when the spinners were on, and hunters killed 4.7 times more mallards. The kill per hour didn't change much as the season went on, either -- the spinners seemed to be as effective in the late season as they were earlier. In his report, Szymanski pointed out that less than six percent of the hunters in the study killed a limit of ducks, even with the help of spinners. Crippling rates in his study did not go down when the spinners were being used.

Another study in Minnesota has found that hunters using spinners killed an average of 16.3 ducks per season, while hunters without spinners averaged less than one bird a season. (It's likely that the hunters using spinning-wings spent more time in the field as well.) Data from Missouri shows that waterfowlers using spinners killed 1.6 birds per day, while hunters without a spinner killed less than one per day. Illinois has collected similar numbers: Hunters using spinners averaged 1.8 ducks a day while hunters without averaged 1.1 a day.

Work in Nebraska has shown that average duck harvest in marshes can be twice as high with spin-wing decoys as it is without. In the late season, mallard harvests may be three to four times higher with spinners.

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