Northern Prairie Wildlife Research Center
Maintaining high breeding duck populations and maximizing recruitment of young are major goals of duck management programs in the midcontinent area. This requires that as many hens as possible survive annual nesting seasons and fledge young. Predation is a strong force that severely hinders efforts to maintain or increase duck production. Our estimated average of 900,000 adult ducks (mostly hen dabbling ducks) taken annually by midcontinent foxes during 1969-73 was a significant loss of prehunting season adults that also resulted in a significant loss of recruitment.
Fox predation on midcontinent ducks has greatest relevance to management of dabbling ducks because they nest primarily in uplands. The predation is widespread and occurs almost everywhere ground nesting ducks and red foxes coexist. During the present study this included most of the midcontinent area.
The impact of red foxes on local duck populations is of special concern to wildlife managers attempting to increase duck production on managed areas. In the midcontinent area the USFWS manages about 196,000 ha of scattered Waterfowl Production Areas primarily for duck production and several hundred thousand hectares of National Wildlife Refuges for many wildlife species including waterfowl (U.S. Fish and Wildlife Service 1983). In addition, the Canadian Wildlife Service, state and provincial conservation agencies, and private organizations manage many thousand hectares in the midcontinent area primarily for waterfowl production (Bellrose 1976:54-56, 514531). Red foxes probably occupied nearly all these areas during the present study and reared pups on many of them.
We do not know the impact of a single fox family on duck production on managed areas, but we believe it is often considerable. Our data for North Dakota show numbers of ducks taken by fox families were highest on areas managed for waterfowl, reflecting higher than average numbers of nesting ducks using those areas. Examples of high predation on managed lands were the 36,42, and 67 ducks found at 3 dens on a wildlife refuge where nesting ducks were abundant. Each of those fox families likely took several times the number of ducks found at their respective dens. Red foxes also are major predators of duck eggs (e.g., Martz 1967, Duebbert and Lokemoen 1976, Higgins 1977). Consequently, we conclude that red foxes are often a major factor that must be considered in the management of ducks on individual production areas.
Predator population reductions that include red foxes have been shown to substantially increase duck production on midcontinent waterfowl management areas (Balser et al. 1968, Duebbert and Kantrud 1974). Although encouragement of fur hunting and trapping is generally a desirable first step to reduce fox populations on such areas, results are unpredictable and the removal of foxes during the fur harvest season may have little effect on fox densities the following spring. This occurs because fox fur harvests are conducted during fall and early winter when pelts are prime. Extensive dispersal of young foxes in fall and winter (Storm et al. 1976:28-47) and strong territorial behavior of resident foxes (Sergeant 1972) result in vacant areas being quickly reoccupied. Control of foxes and other predators in spring is probably necessary for population reduction methods to be effective in substantially reducing predation on nesting waterfowl and their eggs and young.
Predator population reduction is an effective but controversial method for reducing predation on nesting waterfowl. Errington (1964) pointed out that predators living on and around North American wetlands have intrinsic value, and he advised against extreme attitudes toward predator control on behalf of waterfowl management. Nevertheless, he believed that the high red fox and raccoon populations in the midcontinent area during the early 1960's could stand reduction. Leopold (1931:225), in discussing fox predation on bobwhite quail (Colinus virginianus), wrote "the fox question is not so much one of whether foxes do more harm than good, but rather a question of what density of fox population affords that best balance between harm and good."
Potential nonlethal methods of predator management include protecting nesting ducks through use of predator excluding barriers, improvements in nesting cover, and use of aversive and antifertility agents. Such approaches are desirable from many standpoints, but few proven methods are available. Artificial nesting structures are barriers that have been successfully used in many areas to protect nesting wood ducks (Doty and Kruse 1972, Bellrose 1976:56) and mallards (Bishop and Barratt 1970, Doty and Lee 1974) from predators. Electric fences have been successfully tested as a means of excluding foxes and other mammalian carnivores from upland habitats used by nesting ducks (Sergeant et al. 1974, Lokemoen et al. 1982). Water is a natural barrier that in certain situations protects nesting ducks from foxes and other mammalian predators. High densities of nesting ducks with high nesting success have been observed on several mammalian predator-free islands in the midcontinent area (Duebbert 1966, Drewien and Fredrickson 1970, Duebbert et al. 1983). Tall dense cover has been planted near marshes to attract dabbling ducks and to provide increased protection from predators. Some success has been achieved with this method (Duebbert 1969, Duebbert and Lokemoen 1976), but it has proven to be most effective when coupled with predator reductions (Duebbert and Lokemoen 1980). Use of aversive agents, antifertility agents, and possibly scare devices and repellents to directly or indirectly reduce predation has appeal to many waterfowl managers, but information on the effectiveness of such methods is limited. The aversive agent lithium chloride has been tested to alleviate coyote predation on domestic sheep, but results are inconclusive (Lehner 1976, Bourne and Dorrance 1982, Burns 1983). Diethylstilbestrol has been field tested on red foxes in North Dakota but failed to significantly reduce reproductive performance (Allen 1982).
Biological control is a new predator management concept that may have merit in certain situations. For example, knowledge of the inverse relationship between red foxes and coyotes (Johnson and Sargeant 1977:36-40, Sargeant 1982, Voight and Earle 1983) can be used to impact fox densities. Coyote populations in most of the midcontinent area appear to be suppressed by man. Hence, protection of coyotes will result in expansion of local or regional populations that in turn will cause reduction of fox populations. Conversely, reduction of coyote populations provides opportunity for increases in red fox populations, a phenomenon that we believe is primarily responsible for the current abundance of red foxes in much of the midcontinent area. Knowledge of coyote impact on nesting ducks is limited, but recent evidence indicates coyotes have much less impact on upland nesting ducks than red foxes (A. B. Sargeant and S. H. Allen, unpubl. data).
Many questions remain concerning the impact of red foxes and other predators on midcontinent duck populations. Data, however, are sufficient to conclude that predation is a major waterfowl management problem and that predator management schemes that include curtailment of fox predation have potential to greatly increase duck production. As agriculture intensifies and the habitat available to midcontinent ducks dwindles, attention is being increasingly focused on heightened production from remaining habitats, especially managed areas. Managed duck nesting habitats are attractive to predators, and the actions of foxes and other predators in these habitats are in direct conflict with waterfowl production goals. The impact of predators is often so overwhelming that it negates benefits received from habitat management practices. Effective management to increase duck production will necessitate coping with the predation problem. Predator management, like other waterfowl management methods, should be developed, evaluated, and then judiciously applied.