We’ve heard the purported reasons during the past three seasons for poor gunning – short-stopping, sanctuaries, grained refuges, increased hunting pressure, poor breeding conditions and global warming. These are variously cited by hunters, biologists, conservation organizations and waterfowl managers.

Rarely mentioned is hunting, especially the high kills resulting from long seasons and high bag limits of the past few years.

The question that begs to be asked: Are we killing too many ducks?

We can seek insight by creating two simplified, back-of-the-envelope population models.

We begin by looking at U.S. Fish and Wildlife Service mallard breeding population and age-ratio estimates. (The latter is the number of juveniles-per-adult found in hunters’ bags that provides a measure of annual reproductive success.) To avoid statistical anomalies, we will use the annual average for both data sets for the years 2000-02.

MALLARD DATA

We need to make a further adjustment to each of these averages. The U.S. Fish and Wildlife Service estimates the North American breeding survey accounts for 60 percent of the continental mallard population. The total continental mallard population therefore is 13,822,000.

The service also estimates mallard juveniles are 1.51 times more likely to be shot. Therefore, we must adjust the average age-ratio to account for gunning vulnerability. This gives us an adjusted annual age-ratio of .60 juveniles-per-adult.

AGE-RATIO MODEL: We begin by assuming 20 percent of the breeding population dies during the spring-summer period, leaving 80 percent to wing southward. We now can construct an adult fall flight.

As you can see this gives us an average fall flight of 11,057,600 adult mallards.

We also know from age-ratio data there are .60 juveniles-per-adult in the autumn migration, allowing us to calculate the number of juveniles in the fall flight.

We now can tally the total fall flight.

To maintain the mallard breeding population, we must return 13,822,000 mallards (our starting breeding population) to the nesting grounds. Thus, we can calculate the allowable kill.

U.S. Fish and Wildlife Service harvest data estimates the annual 2000-02 U.S. and Canadian mallard kill (retrieved birds, plus 20 per cent cripples) averaged 7,272,883 – nearly double the 3,870,160 allowable kill called for under this model.

NEST-SUCCESS MODEL: We begin this calculation by assuming hens constitute 46 percent of the mallard breeding population. The total number of hens is:

We know that each spring some hens do not nest. Some nest once. Others nest two, three or possibly four times. For this calculation we assume all hens nest twice. Thus, we can calculate the number of nesting attempts.

Biologists believe a 15 percent nest success rate is the minimum necessary for mallards to maintain their population. Therefore, we can calculate the number of successful nestings necessary for mallards to maintain their numbers.

Studies further indicate mallards fledge an average of 5.1 juveniles per each successful nesting. We can now tally the number of juveniles fledged.

The fall flight therefore consists of spring-summer adult survivors and juveniles.

To maintain the breeding population, the allowable kill can be calculated by subtracting the initial breeding population from the fall flight.

Harvest data tells us the annual U.S. and Canadian kill from 2000-02 averaged 7,272,883 – 309,358 more than allowed under our nest-success model.

These two population models strongly suggest that today’s long seasons and high bag limits have caused us to overshoot our mallard breeding flocks, a fact further borne out by nesting-ground surveys. The U.S. Fish and Wildlife Service mallard breeding population fell from 9.5 million in 2000 to 7.8 million in 2003 -- an 18 percent decline.

These population models raise doubts the sport kill “compensates” for natural mortality and does not reduce the breeding population. They also tell us that short-stopping, sanctuaries, grained refuges, etc., are only accessories to the crime. The primary reason for poor hunting in recent years remains the over-shooting of our breeding stocks and subsequent decline in the number of mallards that wing southward each autumn.

Most importantly, the models strongly argue for the imposition of moderate or restrictive gunning regulations in the coming years to allow our breeding stocks to rebuild.