They're Up... They're Down

By Dale Humburg | July 2, 2000
From Missouri Conservationist: Jul 2000

When wild game populations decline, hunters often are the first to suggest restricted seasons. This reflects their strong conservation ethic and general support for wildlife management.

Wildlife populations usually cannot be increased, however, by simply shortening the hunting season or reducing bag limits. Hunting regulations not only must take into account the level of harvest, but also the influence of reproductive capacity, life span and habitat.

Species with short life spans and the ability to produce large numbers of young, such as cottontail rabbits, are not affected by harvest to the same degree as long-lived species, such as deer. A certain compensation also occurs for most species: if the number of animals taken by hunters increases, the number of animals lost to predators, disease or accidents decreases. The capacity for compensation is believed to be greater for short-lived than long-lived species.

It may come as a surprise to learn that regulations are not always designed to maximize population size and harvest. When the Conservation Department sets regulations for dozens of species each year, we also attempt to respond to hunting traditions and hunters' preferences.

Because some hunters' attitudes change each year-often as much as the weather does-it is nearly impossible to respond to short-term changes in hunters' views. We, therefore, make recommendations for hunting regulations based on a combination of population status, long-term average weather, habitat, migration and hunters' input.

Two examples, waterfowl and turkeys, help contrast differences in approaches to regulations, as well as the factors that determine annual population status.

Ducks and Geese

Ducks and geese are migratory species, so hunting regulations governing their harvest are derived internationally. Federal guidelines in Canada and the U.S. provide broad frameworks, from which states and provinces tailor seasons to match specific migration timing, local populations and habitat conditions. The broad guidelines are necessary because we hunt waterfowl for an extended period, from September in Canada through January or later in the southern United States.

Duck populations are dramatically affected by changes in habitat conditions in breeding, migration and wintering areas. When good habitat conditions prevail, as during the mid to late 1990s, ducks flourish and hunting regulations are liberal.

Drought overwhelmed duck habitats during the 1980s and, as duck numbers declined and habitat deteriorated, restrictive seasons were employed to ensure that breeding numbers would be adequate when wetlands again improved.

There is little doubt that duck populations primarily responded to improved wetland conditions during the 1990s. A reduced harvest likely contributed to this recovery.

Harvest also affects Canada goose populations, but not all populations are affected equally. For example, giant Canada geese, which nest in Missouri, rarely experience a poor production season, and because they don't migrate as far as other species, they are exposed to hunting less. They typically survive at a high rate, so hunting regulations for giant Canada geese often are liberal.

In contrast, the Canada geese that nest near Hudson Bay migrate 1,500 miles to Missouri and must run a gauntlet of hunters in Manitoba, Minnesota, South Dakota and Iowa before they arrive. More are taken in Illinois and Arkansas after they leave Missouri.

Additionally, the timing of the spring thaw on northern breeding grounds strongly influences the nesting success of Canada geese. If nesting is delayed past early June, few young geese are added to the population. This "bust" in production occurs about once every 10 years.

Overharvest in these years is devastating because too many breeding-age birds (more than 3 years of age) are harvested, and it takes a few years after the next good nesting season for the breeding population to rebuild. Low harvest and good production both are required for populations to recover.

Most hunters agree with waterfowl hunting restrictions when habitat conditions and population levels dictate. However, they frequently disagree about the timing of the seasons. For example, many goose hunters prefer later seasons that coincide with the arrival of northern geese rather than early seasons scheduled primarily for geese breeding in Missouri.

Likewise, some duck hunters want an early season because they hunt primarily in shallow marshes; other duck hunters want a late season so that freezing water will concentrate birds into open water areas. We try to respond to hunters' preferences as well as biological considerations when we set waterfowl regulations.


The restoration of wild turkeys in Missouri began in the mid 1950s. After initial releases, local populations grew exponentially for the next 20 to 25 years. Closed or restrictive seasons were essential during that period until populations became self-sustaining.

Rapid population growth followed by fluctuating numbers is typical of reintroduced populations. We do not fully understand why this pattern occurs as population densities increase; however, factors such as predation and social interaction among individuals probably play a big role.

Now that turkeys are established in Missouri, their population changes primarily are determined by summer nesting success and recruitment, which in turn are influenced by spring and summer weather conditions. An early spring seems to be associated with higher nesting success, and dry weather during early June results in higher poult survival.

Nest predation may influence nest success, but wild turkeys can produce many young despite high levels of nest predators. Winter conditions generally have little influence on wild turkey population dynamics; however, the availability of winter food in the eastern Ozarks (acorns) can affect nesting success during the breeding season that follows.

Spring and fall wild turkey regulations have different purposes. The primary purpose of spring regulations is to maintain the quality of spring turkey hunting. Spring regulations have little to do with whether turkey populations grow or not. In contrast, fall regulations are set conservatively to minimally impact the population.

Gobblers are important to spring turkey hunters. Thus, hunting regulations for the spring season are primarily set to ensure that less than 35 percent of the male population is harvested. Because only males are killed in the spring (except for a few bearded hens, which are legally taken) and one male will mate with several hens, the harvest has little or no impact on the potential for population growth.

Fall turkey regulations are set to ensure that wild turkeys are not overexploited. A harvest of less than 10 percent of the fall population has little impact on population growth. Because reproduction varies considerably, however, we have maintained a conservative approach to fall turkey seasons. Under current regulations and hunting pressure, less than 3 percent of the fall population is harvested. There is no reason to believe that the fall harvest of turkeys in Missouri affects the numbers of birds available the following spring or the quality of spring hunting.

Hunting regulations help ensure that populations are not overexploited. Wildlife populations change over time, usually prompting renewed scrutiny and possible readjustment of current regulations.

Biologists continue to track numbers, production, habitat conditions, harvest and hunter attitudes. We use this information to recommend seasons that are stable and simple when possible, and we change regulations when necessary to balance species' biology with harvest and hunter preferences.

This Issue's Staff

Editor - Tom Cwynar
Managing Editor - Jim Auckley
Art Editor - Dickson Stauffer
Designer - Tracy Ritter
Artist - Dave Besenger
Artist - Mark Raithel
Photographer - Jim Rathert
Photographer - Cliff White
Staff Writer - Jim Low
Staff Writer - Joan McKee
Composition - Libby Bode Block
Circulation - Bertha Bainer