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Waterfowl Production on the Woodworth Station
in South-central North Dakota, 1965-1981

Conclusion


Generally, the methods used to count or evaluate wetlands, ducks, and vegetation structure were adequate for the study. However, some methods such as the nest surveys and the pair and brood counts required considerable amounts of time and labor to conduct. Of all the kind of data collected, the brood counts were probably the most unreliable because broods are hard to see in vegetated wetlands; if complete brood count data were possible, it would be the most valuable of the data sets.

Our pond occupancy data demonstrates considerable variability among the seasonal time of surveys and the number of wet basins present. Thus, we believe pond occupancy data are poor indexes of specific selection behavior by ducks for various wetland characteristics unless the data are collected in a strictly coordinated effort over time and area.

We found the 1-15 May count usually yielded the best pair population estimates for mallards, northern pintails, canvasbacks, and green-winged teal, and the 20 May-7 June count for all other species. Occasionally, the first count also was used in pair estimates for blue-winged teal. Our recommended census periods approximate those of Dzubin (1969), Smith (1971), and Stoudt (1971).

Annual federal hunting regulations are based,in part, on a single production estimate from data collected in July during aerial brood surveys (Henry et al. 1972). This corresponds to dates when several states, including North Dakota (Schroeder 1971), and several Canadian provinces conduct roadside brood surveys. Based on our hatching chronology data (Table 16), an average of 43% of the potential broods would not have been counted if surveys were made on 10 July, 33% on 15 July, 22% on 20 July, and 15% on 25 July. Similarly, an average of only 50% of duck broods was counted during our July censuses, which approximated the timing of the Service's annual July production surveys. Our study showed that when only one brood survey is made, it should be later in the nesting season, preferably between 25 July and 10 August. However, such a survey would be too late for the present waterfowl regulations-setting schedule.

Ducks nested in all available life-forms and communities of vegetation on the study area and most plant species were associated with duck nests at one time or another during the study. However, wolfberry (Symphoricarpus occidentalis), in our opinion, was the species most important to duck nesting in native prairie habitats whereas alfalfa (Medicago sativa) was the most important forb in planted grasslands.

Predation was a key factor limiting waterfowl reproductive success during the study. Results showed that the effects of predation could be abated by establishing and maintaining good stands of suitable nesting cover and with no major effort to control predator populations during some years. However, management of upland habitats on our large study area only kept the annual nesting populations of waterfowl producing at an average nest success rate slightly above the threshold believed necessary to sustain or increase a population. This was accomplished despite human disturbances necessary to conduct field research; thus, even higher waterfowl production would be expected with good habitat management in the absence of research activities such as occurred on the Woodworth Study Area. However, to increase populations substantially, control of predators or predator access would enhance production even more, especially in combination with good habitat management as demonstrated by Duebbert (1969) and Duebbert and Kantrud (1974).

The greatest loss of ducklings was apparent in the first 2 weeks following hatching. Future research on duckling survival should be emphasized for this age period for all species of ducks. Our results indicate that several species of waterfowl on the 4-km² WSA maintained, but did not increase, their populations under the multiple kinds of land use management, despite current rates of predation and habitat degradation.

Average annual recruitment of ducks can be best enhanced if habitat and predator management strategies focus on successful production from the first (earliest) nesting attempts and on survival of ducklings through their first 2 weeks of life after hatching. Our assessment of waterfowl recruitment would have been enhanced by banding and marking a sample of ducklings and adults annually.

We support Boyd (1973): "If natural resource (waterfowl) management is to be effective in the long-term, it must be based on the identification and understanding of dynamic processes acting over large areas and long periods of time--decades and centuries, rather than days and years." The slowly changing prairie and parkland environment over thousands of years makes even 15-, 20-, and 25-year waterfowl studies seem relatively short-term. Long-term studies usually receive low priority in any administrative system, wherein dollars and labor-hours are limited. Often, it seems apparent that the progression of waterfowl management and research is measured more by the number of job completion reports and publications rather than by our actual accomplishments towards production and solution, no matter how long it may take.

Recommendations

We recommend that long-term waterfowl studies be continued at the Woodworth Study Area and additional locations within broad ecological habitat associations in the glaciated prairie pothole region. Most waterfowl ecology field studies have been relatively short-term because of graduate school tenure, funding allocations, and employee transfer. Even when graduate studies are sequential (e.g., three consecutive 2-year master's programs), their total is still relatively short-term.

If future long-term studies are to be conducted on the WSA or some similar large tract of land, we would also recommend using aerial photography and remote-sensed data to evaluate land use changes, vegetation changes, and wet-dry conditions of wetlands. Use of these procedures would greatly enhance data accuracy and would provide better permanent records of the overall terrestrial aspects for any future study.

Upland-nesting waterfowl were emphasized during this study; in future studies we would recommend more emphasis on over-water nesting waterfowl and shorebirds. We would also recommend a more integrated study approach with special emphasis on predator effects and behavior and on buffer-prey species abundance, particularly of small mammal , passerines, amphibians, and insects. The May breeding pair surveys have usually been concerned only with numbers of wet ponds to describe spring water conditions (U.S. Fish and Wildlife Service 1976). At the WSA between 5 and 10% of the basins did not hold water long enough to be of any substantive value to ducks. Since all (100%) of the basins cannot hold water until the 1-15 May counts, numerically what then constitutes a wet year for ducks, and is it predictable? We arbitrarily referred to a wet year as one in which at least 65% of the basins were full or nearly full to capacity during 1-15 May. There is a strong distinction between basin fullness as compared to just wetness (i.e., numbers of wet ponds regardless of the amount of fullness). We recommend that all agencies making production estimates from pair and brood counts and wet pond counts look deeper at what constitutes a wet pond and its suitability for waterfowl use.

To get reasonable estimates of the nesting population, we recommend a minimum of two pair counts: a first census during the first 2 weeks in May and a second census during the last week of May or the first 2 weeks in June. If possible, the first count should closely coincide with the onset of blue-winged teal nesting and the second with the start of gadwall nesting.

If breeding pairs are to be estimated from one census only, we recommend a count during 20 May-7 June. Occasionally, we noted an influx of mallards during early June; possibly these were pairs that displaced from the intensively-farmed and drained drift prairie area of eastern North Dakota when early nesting attempts were destroyed. The influx of mallards during early June would have less effect on the overall breeding pair estimates if only one count was made during 20 May-7 June, compared to an earlier period when there would be greater numbers of lesser scaup, redheads, and ruddy ducks, many of which would be migrants.

Research is needed on the criteria of what constitutes a blue-winged teal pair. We suspect one female may often be represented by more than one male during the same count, thus, some lone drakes may be bachelor males, At present, each lone drake is representative of a nesting hen in groups of up to five (Hammond 1969).

Compared to Service aerial surveys data, we seldom, if ever, had densities of American wigeon or green-winged teal greater thim 3.2 pairs per square kilometer (2 pairs per square mile), however, the current index adjustment factor for May surveys of ducks increases wigeon numbers by 15 times. We recommend a study to compare present ground and aerial techniques used by various agencies to estimate waterfowl recruitment on the same area.

Research needs to consider a greater species variety of plants to be used in seeding nesting cover. Our study, like many others, dealt primarily with mixtures of tame grasses and legumes. More emphasis should be placed on native grass plantings, on plantings of nesting cover composed of aromatics and armed (thorny, prickly, sawtoothed leaved) vegetation, and on various patterns of cover for greater edge and cover diversity We believe that predator effectiveness might be reduced further by using some of these new cover types.

For lands that have been tilled in the past, we recommend planting nesting cover that is tall. In our study, plantings with a mixture of cool-season grasses and legumes have this characteristic and were rather productive for most upland nesting waterfowl. For lands with native prairie cover, we recommend against the use of annual haying, grazing, or burning, but we encourage periodic manipulations with 1-3-years of rest between treatments for all cover types. We advise a status quo of management operations during and 1 year following all years with extreme wet or dry weather effects, unless there are sound reasons for such decisions. We also recommend that most land-use practices be conducted before 15 April or after 25 July to be least detrimental to nest success.

In this area of the glaciated prairie pothole region, we recommend against starting land-use treatments on duck production lands before 25 July in average or above average precipitation years, and no sooner than 15 July, even in drought years. We also concur with Duebbert and Frank (1984) that 1 August would be the preferable date for initiating mowing on areas managed primarily for production of ground-nesting ducks and winter cover for other wildlife. Further, in many instances, 1 August would also be a preferable initiation date for burning and grazing treatments on native mixed-grass prairie, if the objective is to favor cool-season native plants.

Grazing, burning, haying, and mowing are tools used for managing upland habitats. The timing of these treatments is critical in relation to the potential duck hatch. An appropriate overall land management strategy is to treat only a portion of a management unit because the total land base should not be treated during any one year. However, during drought or other emergency situations, public agencies are often requested to enlarge the amount of land base treated by grazing or haying to satisfy demands of private farmers and ranchers. We suggest that grazing, burning, haying, and mowing treatments be applied periodically in as short of time as possible, and either before or after the nesting season.

Our native prairie habitat research was limited to season-long grazing and to mostly spring burning management. We support expanding of the research to include additional types of specialized grazing systems and to fall burning efforts, both of which show initial promise for increasing waterfowl production for private as well as public lands, and in wetlands as well as uplands.

Generally, nest success averaged greater in larger sized fields. We suggest, where possible, management of fields >8 ha in size would be more beneficial to duck production than fields <8 ha in size, regardless of the upland habitat type. Nelson and Duebbert (1974) and Stoudt (1969) also suggested that nest success was greater in larger fields of cover than in smaller areas.


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