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Table of Contents

• The Recruitment Problem
• The Reason for the Problem
• Waterfowl Production Potential and Challenges

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The Recruitment Problem

Nesting ducks, such as this blue-winged teal hen and its eggs, are extremely vulnerable to predators. In many parts of the prairie pothole region, nest success averages about 10-15 percent and annual recruitment of young is low.

THE PRAIRIE POTHOLE REGION is the primary production area for ducks in the Central and Mississippi flyways. Previous articles in the Naturalist have discussed factors affecting the number and quality of wetlands in this region and the importance of wetlands to waterfowl. Recent studies by us and our co-workers at the Northern Prairie Wildlife Research Center, Jamestown, North Dakota, reveal that in much of the region, mallards and other ducks, face an additional problem. Recruitment, the rate at which breeding hens produce young for the fall population, is alarmingly low in many areas. The purpose of this article is to identify the magnitude of that problem, the major reasons for its occurrence, and the challenge it poses to waterfowl management. Much of the information highlighted by this article is from technical papers that have been or soon will be published.

THE RECRUITMENT PROBLEM

Increases or decreases in duck populations are determined by the delicate balance between births and deaths. For population size to remain constant, numbers of young recruited must equal numbers of adults that die. Waterfowl raise at most only one brood per year. Biologists refer to hen success as the percentage of hens that hatch a clutch of eggs. If the hen's initial nest is destroyed she may nest repeatedly. The proportion of initiated nests that are successful is called nest success. Nest success is one of the most important factors affecting recruitment; if it is low, few young are added to the fall population. Recent studies show that, in most areas of central and eastern North Dakota, less than 15 percent of the duck nests are successful. Results for western Minnesota and eastern South Dakota reveal that nest success is very low in those areas also. In contrast, limited information from northwestern North Dakota and Montana indicates that nest success in those areas is relatively good, about 40 percent in two recent studies. Other studies are currently underway to determine nest success in the Canadian pothole region.

Awareness of low nest success and growing concern over the welfare of the mallard prompted initiation of a detailed study to determine mallard recruitment rates in central North Dakota and to identify the importance of factors affecting recruitment. That study began in 1977 and was completed in 1980.

Recruitment is difficult to measure. During 4 years of the North Dakota study, radio telemetry was used to study 338 mallard hens from shortly after they arrived on the breeding grounds until we knew if they succeeded in rearing young. Radio-equipped hens provided information on nest site selection, nest fate, rate of renesting, and survival of ducklings. The hens were captured throughout a large area to provide results that would reflect general conditions rather than conditions that might pertain to only a local area. This study gave us insight into the relation between prairie duck habitat, predation, and mallard populations.

Radio-marked mallards in central North Dakota showed a preference for road right of ways, odd areas of cover, and hayland as nesting sites and almost complete rejection of annually tilled cropland. Wetland and grassland were used in proportion to their abundance.

Prairie wetlands are dynamic. Weather has a major impact because during drought years the number of ponds is reduced. This impact not only affects the number of pairs attracted to an area but also reduces the nesting effort. The telemetry study revealed that in dry years, on the average, hens attempted only one nest whereas in wet years they averaged 2.6 attempts. Water conditions, therefore, have a powerful impact on recruitment. Ironically, the very droughts that periodically devastate waterfowl production are also responsible for cycles of drying and reflooding that contribute to the fertility of wetland basins and allow high duck production in wet years. Prairie ducks have evolved in this boom or bust environment and are capable of maintaining their numbers provided that nest success is good when water conditions are good. Unfortunately, the telemetry study showed that nest success and, therefore, recruitment was not good during any year.

The prairie pothole region is one of North America's most intensively manipulated environments. Waterfowl biologists have known for years that drainage of wetlands and the less obvious agricultural impacts on wetland quality have gradually decreased the ability of the region to produce large numbers of ducks. Even more drastic changes have occurred on uplands where most dabbling ducks nest. During the past 100 years most of the native grasslands in the Dakotas and western Minnesota have been converted to croplands that are tilled annually. In North Dakota less than 20 percent of the original grasslands remain, and, of those that do, most are heavily grazed. The croplands, under current agricultural practices, are of little value to nesting ducks. On our central North Dakota study area, 38 percent of the area was cropland, but the cropland contained only 2 percent of the mallard nests. In addition, nest success was lower in cropland than in any other habitat. Native grassland and hayland furnished much of the remaining nesting habitat. Much of the grassland was heavily grazed which decreased its attractiveness to nesting mallards. The hayland attracted many hens, but most clutches were destroyed by haying operations. Hens often chose nest sites in odd areas such as fencerows, shelterbelts, and rock piles, but they were generally unsuccessful in these habitats.

The telemetry study revealed that an average of only 8 percent of the nests initiated were successful during the 4 years of the study. These results are similar to those of numerous other studies where nests were found by different methods. At this low rate of nest success only 15 percent of the mallard hens were successful in hatching a clutch, even with persistent renesting.

The principal reason for the low rate of nest success was predation. Seventy percent of the nest failures were known to have resulted from predation, and predators were implicated in many of the remaining nest failures. In addition, predators killed a minimum of 20 percent of the nesting hens. Predators also were strongly implicated in duckling mortality. Twenty-six percent of the broods failed to survive the initial move to water and continuing loss of ducklings resulted in an average brood size of 5 at fledging. The reasons for mortality of ducklings were largely unknown, but predation was the known cause in some deaths.

The important question for waterfowl management is "What impact does the high rate of nest failure and loss of hens and ducklings have on population size?" It is possible to combine an estimate of recruitment and survival to predict population trends. Based on the available data, we conclude that the mallard population in central North Dakota should be declining. If it is not, it must be maintained by birds pioneering to the area from other regions. To obtain population stability, about 30 percent of the hens would have to be successful in one of their nesting attempts. For this to occur, nest success would have to be about 15 percent, as compared with 8 percent observed in the telemetry study.

The Reason for the Problem

Predation ranks high as an important factor in the evolution of prairie ducks. The effects of predation are evident in many characteristics of ducks, such as agile flight, keen eyesight, and cryptic coloration of hens and moulting drakes, as well as distractive behaviors to lure predators from young and feigning death to escape from predators. The anti-predator behaviors of each duck species vary to complement other aspects of their biology, but all are aimed at perpetuating the species. The most important strategy ducks have for coping with predation, and with other environmental stresses, is to produce maximum numbers of young--to overproduce. This strategy increases chances for survival of at least some young. The existence of an annual surplus of ducks is the cornerstone of modern-day waterfowling.

At no time in the annual cycle of ducks is the risk of predation greater than on the breeding grounds. Returning hens space themselves out across the pothole region in the spring where hens on nests expose themselves to predators for about 35 days needed for egg laying and incubation. The risk associated with nesting is a chance that must be taken.

Although prairie ducks have always been subjected to considerable predation, the impact has probably increased in recent decades. In pristine times, ducks lived in habitats largely untouched by man. The impact of predators on duck populations represented a balance that evolved over a long period of time. However, as settlement of the prairie by Europeans progressed, the region and its predator populations were subjected to considerable change. We are still in the midst of this change--man has not yet completed his transformation of the prairie. The consequences of man's impact on prairie duck populations are becoming increasingly clear, and increased predation is one present-day result of that change.

As farming has become less diversified, field size has increased to efficiently utilize modern equipment. Economics has discouraged leaving land idle. These changes are clearly evident from drainage of wetlands, elimination of fencerows, tillage of road ditches, burying of rock piles, increased use of herbicides and insecticides, and new cropping practices. Intensive farming has reduced the amount of prey available to predators during the duck nesting season and has concentrated prey and predator activity in remaining untilled habitats--the same habitat that most ducks use for nesting. Results from a recent study of striped skunks in eastern North Dakota revealed this influence. During spring and summer the skunks foraged primarily for insects and spent about 85 percent of their foraging time in grassland habitats (including road ditches, tree rows, and waterfowl production areas) that represented about 20 percent of the area. The foraging skunks destroyed many duck nests; nest success on the area was about 10 percent.

Another major change affecting prairie ducks has been alteration of the composition and abundance of predator species. Although this change is related to habitat modifications, it also reflects direct human-inflicted mortality of predators. At present, predators having greatest impact on ducks in the Dakotas and western Minnesota include the red fox, striped skunk, raccoon, mink, and Franklin's ground squirrel. Species having lesser impact, but which may be important locally, include the badger, coyote, longtailed weasel, crow, and possibly some gulls and raptors. During pristine times many of these predator species were uncommon or scarce, but other species such as the wolf and kit fox that had an unknown impact on ducks were common.

Settlement of the prairie has benefited most present-day predators. For example, raccoons now have grain to eat and buildings in which to spend the winter and rear young, red foxes have diverse foods including sunflower seeds and livestock carrion during winter, crows and great horned owls have trees for nesting, and mink have impoundments to help them withstand drought. Together, these factors have favored the maintenance of a rather stable, diverse, community of mid-size predators that are highly adapted to prey on ducks, and their eggs and their young.

Direct human impacts have been a major influence on certain predator species; information is best for canids. Wolves suppress coyote populations and coyotes suppress red fox populations. Hence, it is no surprise that after wolves were largely eliminated by man from the pothole region during the mid to late 1800's, the coyote population expanded greatly. Kit foxes disappeared at that time for reasons not fully understood and red foxes became very scarce. Because coyotes preyed on livestock, efforts were undertaken to reduce their numbers. As control became more effective during the 1930's and 1940's, the number of coyotes in farmland areas were reduced substantially and the red fox population began to expand. After 1940 the red fox became far more numerous than ever before in recorded history of the region and during most years occupied almost every square mile of prairie pothole habitat in the eastern Dakotas and western Minnesota. Recently, the coyote population has begun to reoccupy areas where it has been absent for many years and red foxes are becoming less numerous.

Since the mid-1800's canid populations in the eastern portion of the prairie pothole region have undergone considerable change that resulted in an abundance of red foxes during recent decades.

The increase in red foxes after 1940 was detrimental to duck production. Information collected during 1969-73 indicated that about 18 percent of the breeding hen mallards in North Dakota were taken annually by foxes. Most hens were believed killed on nests but some were scavenged. Other information showed that individual fox families often take 40 or more adult ducks in spring (mostly hen dabbling ducks) and that foxes have a particularly strong attraction to duck eggs. Information about the impact of coyotes on ducks is scant, but it appears that coyote predation on ducks and duck eggs is much less severe than red fox predation. The relatively high nesting success reported for northwestern North Dakota and Montana was in areas where coyotes were numerous.

The red fox is abundant throughout the eastern Dakotas and western Minnesota and is an effective predator of upland nesting ducks and their eggs.

The environmental changes that have occurred in the prairie pothole region create special problems for prairie ducks. The loss of wetland habitat poses the greatest threat. Although wetland habitat guarantees a place for breeding ducks, it does not guarantee that hens will fledge young. The problem of high predation on adult ducks, eggs, and young, and its underlying cause, an environment that has been drastically altered, poses a challenge to waterfowl management.

Waterfowl Production Potential and Challenges

When ducks arrive on their prairie breeding grounds each spring, they have available a mosaic of wetland and upland habitats in which to nest and rear their young. Intensive agricultural practices have resulted in a general deterioration in the wetland and upland habitat base for breeding waterfowl. Most biologists would agree that this trend is likely to continue, but some changes may occur that will benefit prairie ducks. For example, duck recruitment would be improved if land retirement programs could be modified to provide large acreages of undisturbed grass-legume cover for 3-5 years. Also, the current trend toward minimum-till and no-till farming methods may benefit nesting ducks. Managers of the wildlife resource have had little influence on major land-use decisions on private land, but they should be alert to ways that Federal farm programs were modified to produce benefits to wildlife. Waterfowl managers should also be sensitive to changes in predator populations that may occur as a result of disease, harvest impacts, or habitat change and thus affect waterfowl recruitment.

In North Dakota conversion of prairie grasslands to annually tilled cropland has created problems for upland nesting ducks.

Under current farming practices and predator populations, waterfowl recruitment rates are low and are cause for concern. If the capability for waterfowl production on private land continues to decline, increased recruitment of waterfowl on managed areas will assume greater significance. Fortunately, Federal and State agencies control a habitat base upon which management can be practiced to increase recruitment. Certain prairie ducks, especially mallards, are endowed with physiological and behavioral attributes that make them well-suited for the production of large numbers of young on small areas of habitat if adequate complexes of wetlands and uplands remain and high nest success can be assured. Natural prairie wetlands provide aquatic habitat of outstanding quality for supplying the spatial and food requirements of breeding waterfowl. Federal and State agencies have preserved many thousands of acres of wetlands and adjacent uplands to be managed for waterfowl production. Compared to the total area in the prairie pothole region, the amount of habitat that can be managed specifically for waterfowl is small but it is of high quality and has potential for producing large numbers of waterfowl.

Results of several research projects provide hope that high levels of waterfowl production, particularly that of mallards, can be attained on managed areas. One such study was conducted in the pothole region of north-central South Dakota during 1971-73. That study evaluated duck nest densities and success in 9 fields (40-100 acres) of undisturbed grass-legume cover. The fields were in an area with good complexes of natural wetlands and good populations of breeding ducks. Results of the study indicated that many more ducks, especially mallards, nested in the plots of managed cover than in farmed or grazed plots. Nest success was about 20 percent higher on the managed tracts than on unmanaged areas. The major finding of this study was that nesting ducks can be attracted to fields of tall, dense cover. In some instances, however, predators negate the positive effects of habitat management.

Highest duck production consistently occurs in areas where habitat is good and predation is greatly reduced either naturally or by management. In the same region where the above study was conducted, 1,062 nests of 7 duck species were found from 1969 to 1974 on a single 125-acre field in an area where mammalian predators, especially red fox, striped skunk, raccoon, and badger, were controlled. Nest success was 94 percent when control of these predators was nearly total. At least 7,250 ducklings were hatched on the field during the 6 years of the study. There did not appear to be anything unique about the study area except for the removal of predators. This study illustrated dramatically the high reproductive potential of wild ducks, especially mallards, in good habitat if they are protected from the negative influence of predation.

Islands in certain lakes also provide examples of how large numbers of ducks can be produced on small units of habitat free of predators. In 1978 and 1980, duck nesting was studied on 15 islands in Audubon National Wildlife Refuge in North Dakota. On these islands (45 acres total area) there were 458 waterfowl nests of 10 species and nest success was 86 percent. Mallards and gadwalls were the principal species. One of the densest concentrations of nesting mallards ever found in North America occurred on an 8-acre island in Miller Lake in northwestern North Dakota. Duck nesting on this island was studied during 1976-80. In 1977, 385 mallard nests were found; over 200 nests were found in each of the other years. The principal nesting cover was 2 acres of dense western snowberry (buckbrush) and Wood's rose which contained 97 percent of the nests. During the 5 years, there were at least 2,560 duck nests on the island. Nest success averaged 85 percent and a minimum of 16,000 ducklings were hatched.

Islands in large lakes are productive of ducks because the water provides a natural barrier to predators.

Islands and direct predator control have obvious implications for waterfowl management, but the application of these practices may be curtailed by economic, ecological, or sociological considerations. Methods to separate mammalian predators from hens and eggs during the nesting season are needed. One technique that showed promise was the placement of electric fences around plots of high-quality managed cover. A study conducted in eastern North Dakota and western Minnesota showed that nesting success was increased markedly by protecting nesting cover with electric fences. Nest success averaged from 20 to 45 percent higher in the protected areas than in unprotected areas. Recent studies in North Dakota have shown even more dramatic differences between fenced and unfenced areas.

Radio-marked mallards in central North Dakota showed a preference for road right of ways, odd areas of cover, and hayland as nesting sites and almost complete rejection of annually tilled cropland. Wetland and grassland were used in proportion to their abundance.

On the basis of the above information and what is known about the behavior and physiology of prairie ducks, it may be possible to develop effective strategies for high production. The mallard is regarded as the most highly sought duck by North American duck hunters and it is well-suited for intensive management. On the breeding grounds, pairs are highly mobile and will fly long distances from suitable feeding and loafing areas to utilize desirable nesting sites. Hens and broods are capable of long movements to utilize preferred brood-rearing habitat. Mallards are long-lived birds and hens that hatch a clutch of eggs will usually return the next year. If high waterfowl production is desired, management practices must be developed that allow prairie ducks to attain their innately high reproductive potential. Extensive knowledge is available on how to establish and maintain nesting cover, but at present there are few acceptable methods available for alleviating predation.

The impact of environmental change, including predation, on prairie ducks is severe and may get worse. Nevertheless, there is reason to be optimistic about the future if a good wetland habitat base can be preserved, uplands are properly managed, and the adverse impact of predation can be alleviated.

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