Duck Nests Research Articles

Foods of American Badgers in West-central Minnesota and Southeastern North Dakota During the Duck Nesting Season

Abstract Although the American badger (Taxidea taxus) is common in grasslands and preys on a wide diversity of foods including birds, little is known about badger diet in areas where nesting ducks are common. Small mammals, primarily Muridae and Geomyidae, were the most common food items in the diet of badgers collected from west-central Minnesota and southeastern North Dakota during April–July 1987 through 1990, based on analysis of gastrointestinal tracts of 47 adult (≥1-y-old) and 5 juvenile (<6-mo-old) badgers. Remains of mammals occurred in 98% of samples from adult badgers. Small quantities of insects were found in 40% of adult samples. Bird remains were in 32% of adult samples, most birds identified as Anatidae; ducks or ducklings occurred in 27% and duck eggs in 60% of those samples. Remains of reptiles, amphibians and mollusks were present, but were less common than other foods. Insects and bird eggs were more common during spring (April–May) than summer (June–July). Birds were more frequent in d...

Effectiveness of Dense Nesting Cover for Increasing Duck Production in Saskatchewan

We conducted a 3-year study (1992-94) in the parkland of southern Saskatchewan to evaluate effectiveness of dense nesting cover (DNC) as a means of increasing duck production in prairie-parkland nesting areas. Nest searches were conducted on 31 DNC plots and 31 unmanaged plots (UM). Mallard (Anas platyrhynchos), gadwall (A. strepera), northern shoveler (A. clypcata), and blue-winged teal (A discors) initiate<] 90% of the duck nests found. We restricted our analysis to nests of these 4 species (n = 997) to facilitate interspecific comparisons. Mean Mavfield nest success for the 4 duck species combined was greater (P = 0.038) in DNC (15%) than in UM (7% ) over the 3-year period. However, there was a significant species × treatment interaction (P = 0.038): mallard and gadwall had higher (P = 0.005) nest success in DNC (14-16%) than in UM (4%), whereas blue-winged teal and northern shoveler did not (10-15% in DNC vs. 10-14% in UM). Of the factors we examined year had the greatest effect on nest success (P = 0.002) For the 4 species combined. nest success varied among years from 8-26% in DNC and 4-16% in UM. Nest success also was highly variable among plots within years. Although the nest-success rate of mallards in 2 of 3 years exceeded the threshold (15%) considered necessary fo a stable population (16% in 1992, 24% in 1994), it was only 7% in 1993. Nest densities in DNC calculated from mean Mayfield nest-success rates and corrected for nest-search efficiency ranged from 1.1 to 1.4 nests/ha. Given the nest-success rates and densities observed, DNC would have to be established on a prohibitively large area to effect a substantial increase in regional duck production We recommend placement strategies for DNC plots and suggest increased conversion of cultivated land to pasture may be a more cost-effective strategy for increasing duck nunbers on the Canadian prairies.

Duck nesting success in a fragmented prairie landscape: is edge effect important?

Habitat fragmentation and the creation of extensive edges have been postulated as causes of higher nest predation in many species of birds. In this study we tested the hypothesis that predation on upland duck nests was influenced by proximity to habitat edges in a fragmented agricultural landscape of the Canadian prairies. Nest success was independent of distance to wetland edge, road edge, or different habitat ecotones for mallard ( Anas platyrhynchos), gadwall ( A. strepera) and blue-winged teal ( A. discors). The observed distribution of mallard and gadwall nests relative to wetland edges and habitat ecotones followed the random model, while nests were located closer to roads than expected. Nests of blue-winged teal were distributed closer to wetland edges and roads than predicted by random distributions, however, nests relative to habitat ecotones followed a random pattern. Overall, mammalian predation appeared to be the main cause of nest destruction. Nests in a fragmented prairie landscape are subjected to heavy predation, but this is not necessarily related to proximity to edges.

Effects of Human Disturbance on Success of Artificial Duck Nests

Waterfowl management on the breeding grounds focuses on improving nest success. Gauging the success of habitat management often depends on measures of nest success, yet the effect of researchers on nest failure is not well known. We used artificial duck nests to determine the effect of human disturbance on nest success in the Prairie Pothole Region in southwestern Manitoba, Canada. We created nests with and without human trails leading to them in 3 types of cover: wetland edge, dense nesting cover, and roadside right-of-way. In wetland edges, nests with trails were depredated more often (P = 0.003) than nests without trails during 1993 but not 1994 (P = 0.317). In roadside right-of-way habitat during 1993, rates of nest destruction did not differ (P = 0.072) between nests with and without trails. In 1994, however, nests in roadside right-of-way habitat with an observer's trail were preyed upon more often than nests without trails in 2 trials (Trial 1: P = 0.025; Trial 2: P = 0.003). In dense nesting cover, predation of nests was not affected by presence of observer trails in either 1993 (P = 0.439) or 1994 (P = 1.000). We placed duck feces on artificial nests, which were then depredated more often (P = 0.020) than nests without such odors. We also found nests created with damaged eggs were depredated substantially more often (P < 0.001) than nests without damaged eggs. Our work demonstrates increased egg losses associated with duck feces and cracked eggs, but the effects of a human trail to the nest were equivocal.

The Impact of CRP on Avian Wildlife: A Review

We reviewed the literature to assess the impact of the Conservation Reserve Program (CRP) on bird populations in the central USA. The CRP replaced production agriculture fields with grassland habitat used by more than 90 species of birds. At least 42 bird species nested in CRP habitats. Bird species richness in CRP fields was similar to that in rowcrop fields, but relative abundance was 1.4 to 10.5 times higher in CRP plantings. Nest abundance was 13.5 times higher in CRP than crop fields, although nesting success of songbirds was only slightly higher in CRP fields (40% vs. 36% in crops). Limited evidence suggests that the CRP has positively affected the population growth rates of several nongame grassland bird species. Waterfowl nest densities and nesting success in CRP fields were similar to those occurring in grassland habitats managed specifically for waterfowl. The presence of CRP grassland has been postulated to have improved the quality of existing duck nest habitat by dispersing nests over a larger area. Ring-necked pheasant (Phasianus colchicus L.) populations seemingly increased substantially with CRP acres. Little evidence of positive population response by northern bobwhites (Colinus virginianus L.) to the CRP is available. Overall, grassland birds known to be declining throughout North America were seemingly the most benefitted by the CRP.

Frequency of Nest Box Maintenance: Effects on Wood Duck Nesting in South Carolina

We varied the frequency that wood duck (Aix sponsa) nest boxes were cleaned of nesting materials (i.e., down feathers, egg membranes and shells, and unhatched eggs) in the breeding season to test effects of different maintenance schedules on frequency of nest box use and production of eggs and ducklings. We also tested whether varying the frequency of nest checks influenced accuracy of nesting data. There were fewer nests, eggs, and ducklings produced in nest boxes that were not cleaned of nesting materials than in nest boxes cleaned of nesting materials one or more times during the breeding season. Nest success did not differ among maintenance schedules, but hatching success was greater in nest boxes cleaned out at least once. For nest boxes first checked in April, an independent biologist's estimates of nest box use, nests per box, and successful nests per box did not differ from data gathered during weekly nest box inspections. Total numbers of eggs and ducklings produced per box, however, were underestimated by the independent biologist. These boxes were checked once more by the biologist after the breeding season in August, and production of eggs and ducklings (Apr-Aug) again were underestimated. Nest boxes never cleaned out in the breeding season were checked by the independent biologist in August; all measures of nesting frequency and productivity were greatly underestimated. We recommend assessing nesting activity in boxes and removing old nest materials once after the peak of nesting and again immediately after the breeding season to maximize nest box use and duckling production and to provide accurate estimates of nest box use, nests per box, and successful nests per box. More frequent monitoring of nest boxes will be needed, if accurate estimates of egg and duckling production are required.

Making Sense of Scents: Effects of Odour on Survival of Simulated Duck Nests

It is unclear whether natural odours, including those associated with faeces or feathers, affect clutch survival in waterfowl and other ground-nesting birds because results of previous studies are'potentially confounded by effects of nest density and habitat features. Thus, we conducted 6 experiments (40-125 clutches/test) over 3 years with natural and novel odours, evaluating effects on survival of simulated clutches (3-4 chicken eggs) while controlling nest density, habitat, clutch concealment, frequency of visits and local patterns of predation. Clutches treated with commercial duck scent, pond water, or a novel odour survived as well as controls. In a dose-response experiment, clutch survival did not vary with the amount of commercial duck scent. However, clutch survival declined with the addition of Mallard Anas platyrhynchos faeces mixed with pond water and, to a lesser extent, with down feathers removed from hatched nests. Higher survival of simulated nests relative to natural ones may be associated with differences in odours. Furthermore, nest predation may rise in the vicinity of nests when human visits cause birds to defecate on or near their nests.

Long-Term Declines in Nest Success of Prairie Ducks

Increased predation on nests of ducks in prairie uplands, as a result of habitat alteration, has been hypothesized to cause decreased nest success and population sizes. We tested whether, and by how much, nest success declined using data compiled from 37 studies conducted between 1935 and 1992 at 67 sites in the Prairie Pothole Region of Canada and the United States. Nest success declined (P = 0.0002) over time, but time explained only 10% of the variation ; precipitation (P = 0.79) did not account for additional variation in nest success. Nest success declined at similar (P = 0.13) rates among 5 species, but late nesters (gadwall [Anas strepera], blue-winged teal [A. discors], and northern shoveler [A. clypeata]) had higher success (P = 0.004) than early nesters (mallard [A. platyrhynchos], and northern pintail [A. acuta]). Populations of gadwalls and northern shovelers, however, have not declined, indicating that declines in nest success may not be related causally to population change. Long-term population declines in blue-winged teal, northern pintails, and mallards coincide with large-scale temporal declines in nest success. Declines in nest success were parallel in parkland and grassland regions, suggesting a causal agent (or agents) that act(s) at a broad scale, despite inherent differences in the composition of the predator communities and habitats between regions.

Duck Nest Success Declines with and without Predator Management

The decline in nest success of upland nesting ducks in the Prairie Pothole Region has been hypothesized to have been caused by increased predation coincident with habitat alteration. We tested this by comparing data on nest success from 21 studies conducted between 1937 and 1990 at sites where principally mammalian predators were removed by trapping, shooting or poisoning, or were presumed absent from either islands or fenced exclosures, with data previously compiled from 37 studies conducted between 1935 and 1992 at sites where predators were not reported removed by any means. Nest success was greater (P < 0.0001) on islands and in fenced exclosures than at removal and unmanaged sites. However, nest success declined (P < 0.0001) over time at similar (P < 0.13) rates where predators were managed and unmanaged. Thus, where nest predators can be excluded, increased nest success results, but nest loss to mammalian predators does not appear to be the cause of the long-term decline in nest success.

Predation on artificial duck nests in a fragmented prairie landscape

:Fragmentation and degradation of the natural prairie landscape by agricultural practices has resulted in the creation of numerous man-made edges and relatively small plots, which may lead to higher predation rates on nests of upland nesting ducks. We placed artificial duck nests (n = 1110) at various distances from edge to test the hypothesis that nest predation was influenced by proximity to habitat edge. In large plots (200 ha), nest survival increased with distance from edge up to 250 m, but then declined. In small plots (50 ha), no significant edge effect was detected. Overall, nest success was similar in large and small plots. Nest survival differed among habitat types. In large plots, survival was greatest in delayed hay fields, intermediate in native grassland, and lowest along rights-of-way. In small plots, survival was greater in native grassland compared with delayed hay. Overall, more mammals than birds depredated nests and striped skunks (Mephitis mephitis) destroyed most of the nests. In large plots, more nests along edges were depredated by striped skunks than by other mammalian predators. Similarly, along rights-of-way, striped skunks destroyed more nests than did other mammalian species.

Patterns of Wood Duck Nest Temperatures during Egg-Laying and Incubation

We studied the thermal environment of Wood Duck (Aix sponsa) nests in southeastern British Columbia. Mean daily nest temperatures (T N ) were correlated with maximum daily air temperatures. T N increased as the egg-laying period advanced among both successful and unsuccessful nests, although T N was lower among unsuccessful nests. Hens began spending nights on nests when there were as few as four eggs in clutches. T N and the precision of nest thermoregulation increased among successful nests as the incubation period advanced, although there was a great deal of variation between days and nests. Length of the incubation period was not correlated with clutch size, nor with mean overall nest temperature during incubation, but was correlated with the variance of T N 's during incubation.

Factors Influencing Wood Duck Use of Natural Cavities

The lack of suitable cavities is a primary limiting resource for wood ducks (Aix sponsa). We studied wood duck nest site selection, nest success, and use of cavities by other vertebrates at Muscatatuck National Wildlife Refuge (NWR), southcentral Indiana, in 1984-85. Of 789 surveyed tree cavities, 15% (122) were suitable for wood duck nesting. Minimum nest densities were 0.13 ± 0.08 (SE) nest/ha in 1984 and 0.08 ± 0.03 in 1985; 7-9% of the suitable cavities were used by wood ducks. Density of suitable cavities was higher (P < 0.001) in areas with mature or sawlog trees (1.69 ± 0.22 cavities/ha) than in areas with smaller trees (0.31 ± O.11 cavity/ha). American beech (Fagus grandifolia), red maple (Acer rubrum), and American sycamore (Platanus occidentalis) produced 72% of suitable cavities, but composed only 28% of the basal area. We estimated an annual survival probability of 0.91 for suitable cavities during the study. Cavities with vertically facing entrances were used in greater proportion than other cavity types (P = 0.006). Cavity volume, entrance area, and diameter of the bole at entrance were important in distinguishing cavities used by wood ducks (n = 21), fox squirrels (Sciurus niger; n = 29), and raccoon (Procyon lotor; n = 22) in 1985. Distance to nearest water in early spring was greater for successful nests (P = 0.017) than for unsuccessful nests, probably because of raccoon foraging behavior. Daily survival rate for nests was 0.963 ± 0.01 and estimated nest success was 0.22. Wood duck production at Muscatatuck NWR was limited by raccoon predation and not by nest site availability

Differential Effects of Coyotes and Red Foxes on Duck Nest Success

Low recruitment rates prevail among ducks in the Prairie Pothole Region of North America, primarily because of high nest depredation rates. The red fox (Vulpes vulpes) is a major predator of duck eggs, but fox abundance is depressed by coyotes (Canis latrans). We tested the hypothesis that nest success of upland-nesting ducks is higher in areas with coyotes than in areas with red foxes. We conducted the study during 1990-92 in uplands of 36 areas managed for nesting ducks in North Dakota and South Dakota. Overall nest succes averaged 32% (95% CI = 25-40) on 17 study areas where coyotes were the principal canid and 17% (CI = 11-25) on 13 study areas where red foxes were the principal canid (P = 0.01). Both canids were common on 6 other areas, where nest success averaged 25% (CI = 13-47). Habitat composition, predator communities with the exception of canids, and species composition of duck nests in coyote and red fox areas were similar overall. Upon examining only nests with ≥6 eggs on the last visit prior to hatch or depredation, we determined nests with evidence characteristic of fox predation accounted for 4% of depredated nests in coyote areas and 27% in fox areas (P = 0.001). An expanding coyote population is contributing to higher overall nest success. Management of coyotes may be an effective method for increasing duck nest success

Timing of Nest Searches for Upland Nesting Waterfowl

Searches for duck nests should maximize the probability of locating nests, while minimizing the possibility of causing nest abandonment. Thus, we collected nest attendance data for 44 mallard (Anas platyrhynchos), 13 blue-winged teal (A. discors), 12 lesser scaup (Aythya affinis), 8 northern shoveler (Anas clypeata), 6 gadwall (A. strepera), and 4 green-winged teal (A. crecca) females to determine the optimal times of day to search for active nests. Females of most species attended nests from 0800 to 1400 central standard time (CST). The overall probability of nest attendance during this time was 91.4 ± 2.6 (SE) %. Consequently, nest searches for upland nesting waterfowl should be initiated after 0800 and should be terminated by 1400 CST

Factors Influencing Depredation of Artificial Duck Nests

Because artificial nests can facilitate controlled experiments of nest success, we used them to assess whether human visitation, nest density, vegetation structure, and proximity to habitat edge could affect depredation of duck nests on Yukon Flats National Wildlife Refuge, Alaska. More (P 0.05) between depredated and undisturbed nests

Factors Affecting Egg Predation by American Crows

We studied predation by breeding American crows (Corvus brachyrhynchos) on artificial duck nests in upland and overwater habitats from April to July in 1986 and 1987 in the prairie pothole region of southwestern Manitoba, Canada. Predation was higher on nests placed within home ranges of breeding crows than on nests placed at random locations outside of home ranges. However, artificial nests placed >700 m from crow nests, yet within home ranges, were relatively safe from predation. Predation was greater on upland than on overwater nests. Nests in low vegetation were most vulnerable to crows, but increases in cover height above 20-50 cm did not substantially reduce predation. J. WILDL. MANAGE. 54(3):433-437 The possibility that egg predation has depressed waterfowl nesting success throughout the prairie pothole region (Cowardin et al. 1985, Greenwood et al. 1987) is of concern to waterfowl managers because this region is an important breeding area (Smith et al. 1964, Batt et al. 1989). Increasing nest success in the prairie pothole region is a goal of the North American Waterfowl Management Plan (Can. Wildl. Serv. and U.S. Fish Wildl. Serv. 1986). Electric fences are sometimes used to exclude predators from habitat managed for nesting waterfowl (Lokemoen et al. 1982). However, these fences cannot exclude avian species such as American crows, which are recognized as important predators of waterfowl eggs (e.g., Kalmbach 1937, Johnson et al. 1989). Egg predation by crows seldom has been investigated in detail, yet such data are needed to improve waterfowl management decisions in areas where crows are potential predators. Sugden and Beyersbergen (1986, 1987) found that crows that searched on foot located more artificial nests when nests were clumped rather than dispersed and were located in vegetation short and sparse rather than tall and dense. We compared rates of predation by crows on artificial duck nests: (1) during different stages of crow nesting cycles, (2) in upland and overwater sites, (3) in different vegetation types, (4) within and outside breeding crow home ranges, (5) at varying distances from active crow nests, and (6) in different heights of vegetation. Our study was not designed to estimate predation rates on wild duck nests. Rather, we used artificial nests as a tool to examine how nest site characteristics affected predation rates by crows, but Gdtmark et al. (1990) showed that predation rates on artificial and natural nests can be similar. This project was funded by the North American Wildlife Foundation through the Delta Waterfowl and Wetlands Research Station, and Iowa State University through the Department of Animal Ecology and the Iowa Agriculture and Home Economics Experiment Station. We thank J. M. Buenger, R. J. Keith, and D. M. Richardson for assistance in collecting data, and D. C. Glenn-Lewin, R. J. Greenwood, D. H. Johnson, E. E. Klaas, and L. G. Sugden for providing critical comments on the manuscript. M. G. Anderson, A. B. Sargeant, and L. G. Sugden provided valuable insight during the formative stages of the study. This is Journal Paper J-13149 of the Iowa Agriculture and Home Economics Experiment Station, Ames, Iowa, Project 2466.

Reducing Mammalian Predation on Eggs by Using a Conditioned Taste Aversion to Deceive Predators

When chicken eggs injected with 20-25 mg of emetine dihydrochloride were distributed along 3 different 0.7-1.0-km transects, mammalian predators that had been feeding on untreated eggs developed a conditioned taste aversion and reduced their consumption of treated eggs by >75%. The predators, primarily raccoons (Procyon lotor), opossums (Didelphis virginiana), and striped skunks (Mephitis mephitis), continued to avoid untreated chicken eggs placed subsequently. In another experiment, equal numbers of emetinetreated and untreated eggs were distributed simultaneously along 4 different transects. Egg depredation rates were compared to depredation rates along 4 nearby transects where only untreated eggs were distributed. Egg depredation rates at treated and untreated sites did not differ during the 4-week test. Thus, it might be possible to reduce egg depredation by mammals by distributing emetine-treated egg baits prior to the onset of egg laying, but not after laying has begun. J. WILDL. MANAGE. 54(2):360-365 Mammalian predators reduce the reproductive success of many birds (Ricklefs 1969). From a human perspective, predation of eggs is a problem when poultry, endangered species, gamebirds, or other highly valued species are victimized. For instance, 1 critical problem is high predation rates on duck nests in the midcontinental prairie wetland region (Klett et al. 1988). The usual, effective, and cost-efficient method to reduce egg loss is to remove predators through poisons, shooting, or trapping (Balser et al. 1968, Duebbert and Lokemoen 1980, Lokemoen 1984). The benefits of removal, however, are usually short-term because the predators removed are quickly replaced (Duebbert and Kantrud 1974, Lokemoen 1984, Greenwood 1986). Moreover, removal is often controversial because the predators are valuable, and their removal might inadvertently produce other problems (Sargeant et al. 1984). Another potential way to reduce egg predation is to teach predators that ingestion of eggs might be followed by gastrointestinal illness, causing the predators to develop a conditioned taste aversion (CTA) to eggs. CTA's have been tested as a method to reduce coyote predation on sheep, but the results have been mixed (Conover et al. 1977, 1979; Conover 1982; Burns and Connolly 1985; Ellins 1985; Forthman Quick et al. 1985; Lehner and Horn 1985; Wade 1985). Successful applications of CTA's have been limited primarily to reducing bird damage to seeds and ripening berries: situations where the chemical is directly sprayed on the food (Stickley and Guarino 1972, Guarino et al. 1974, Stone et al. 1974). Unfortunately, it is impractical to chemically treat the eggs of free-ranging birds so that a predator will become ill after consuming one. Spraying chemicals on eggs, for instance, may be ineffective because most predators do not eat egg shells, and injecting the chemical inside the egg could kill the embryo. Furthermore, searching for hidden nests would be laborious. An alternative is to deceive predators by scattering out eggs injected with an aversive-conditioning chemical before the onset of egg laying. Theoretically, predators should develop a CTA to the treated eggs, generalize the aversion to untreated eggs, and stop depredating all eggs (Conover 1984). Some researchers have tried to reduce predation on eggs using CTA's, but none have successfully reduced predation on untreated eggs (Hanners and Southern 1980, Nicolaus 1987). In the most successful test, American crows (Corvus brachyrhynchos) were averted from green-painted eggs after ingesting other green-painted eggs injected with a chemical that made them ill. They did not, however, stop eating unpainted eggs (Nicolaus et al. 1983). Recently, I found that a 25-50 mg dose of emetine dihydrochloride (emetine) not only averted captive raccoons from treated food (including chicken eggs) but also caused them to generalize the aversion to the same food when untreated (Conover 1989). Emetine is a toxic substance with medicinal uses (Klatskin and Friedman 1948, Sax 1984); it is one of the active ingredients in ipecac syrup that is administered to humans to induce vomiting following inges-

Wood Duck Nest Sites in Bottomland Hardwood Forests of Mississippi

We studied the occurrence of natural cavities suitable for wood duck (Aix sponsa) nest sites in mature bottomland hardwood forests on Noxubee National Wildlife Refuge (NNWR) and Delta National Forest (DNF), Mississippi in 1985 and 1986. We found 0.19 ? 0.09 (SE) and 0.23 ? 0.13 suitable cavities/ ha on NNWR and DNF, respectively. Sycamore (Platanus occidentalis) and beech (Fagus grandifolia) trees contained 60% of the suitable cavities on NNWR, but composed only 2.6% of the available trees. Cavity rates on the 2 areas were among the lowest reported for mature forests in North America. The paucity of suitable cavities suggests nest box programs are more important to maintain breeding populations of wood ducks in riparian bottomland forests of the lower Mississippi Valley and the Gulf Coastal Plain than has recently been reported along the northern edge of their range. J. WILDL. MANAGE. 53(2):378-382 The lack of natural nest sites is a factor limiting nesting wood duck populations (Hawkins and Bellrose 1940, McLaughlin and Grice 1952, Haartman 1957, McGilvery 1968). However, guidelines for nest box programs vary among regions of the U.S. Fish and Wildlife Service (USFWS); personnel in some regions have suggested that artificial nesting structures be used for research, demonstration, and other special purposes rather than as a principal means of achieving production goals (USFWS 1982). Under these guidelines and cost constraints, some USFWS refuge managers were gradually phasing out wood duck nest box programs (J. L. Tisdale, NNWR, pers. commun.). The value of nest box programs for wood ducks in Wisconsin has been questioned on the basis that an overwhelming preponderance of production occurred in natural cavities (Soulliere 1986) that were estimated to far exceed needs of the nesting population (Soulliere 1988). Studies of wood duck nest sites on 16 areas (Lowney 1987) from Canada (Prince 1968) to Mississippi (Woods 1964) have reported from 5.44 to 0.08 nest sites/ha, respectively. Studies of cavity occurrence in bottomlands in the central and southeastern United States suggest that the occurrence of suitable cavities for wood duck nest sites is often <1/ha. However, estimates from southern areas were limited by data that were collected from small areas (Woods 1964, Teels 1975), cutover stands (Weier 1966), altered stands (Strange et al. 1971), or combinations of these. Information on natural cavity occurrence by stand type and tree species characteristic of the southeastern United States is needed. We report on the occurrence rates of natural cavities in mature bottomland hardwood forests of the Gulf Coastal Plain and the lower Mississippi River Valley floodplain. We thank K. M. Blanton, D. T. Reinke, R. E. Herring, and P. A. Morrison for field assistance. G. A. Hurst, R. M. Kaminski, and R. J. Muncy review d the manuscript. Funding was provided by Mississippi Cooperative Fish and Wildlife Research Unit and Mrs. C. B. Bradley. The Mississippi Department of Wildlife Conservation, Wildl fe Management Institute, Mississippi State University, USFWS, NNWR cooperate with the Mississippi Cooperative Fish and Wildlife Research Unit.

Movements and Habitat Use of Franklin's Ground Squirrels in Duck-Nesting Habitat

We used radio telemetry to determine the movements and habitat use patterns of adult Franklin's ground squirrels (Spermophilus franklinii) on a 152-ha Waterfowl Production Area (WPA) in central North Dakota. The squirrels were diurnal. Mean total distance traveled daily was 213 and 153 m for males and females, respectively. Movements of females decreased during gestation and lactation; those of both sexes decreased prior to immergence. Annual home ranges averaged 24.6 and 8.7 ha for males and females, respectively; biweekly home-range sizes exhibited seasonal patterns. Ground squirrels restricted their activities almost exclusively to the WPA. Use of blocks of herbaceous cover on the WPA could not be explained by vegetation height, density, or litter depth. Ground squirrel movements were influenced by locations of burrow systems and patchily distributed food resources. Periodic cultivation or removal of herbaceous vegetation may inhibit use of upland duck-nesting habitat by ground squirrels. J. WILDL. MANAGE. 53(2):324-331 Planting dense nesting cover (DNC) to provide upland-nesting ducks with increased security from nest predators is a common practice on areas managed for duck production in North America's prairie pothole region (Duebbert and Kantrud 1974, Duebbert and Lokemoen 1976, Higgins and Barker 1982). Although DNC is attractive to some duck species, its importance to the activities of predators of duck eggs is undetermined. The Franklin's ground squirrel inhabits dense cover throughout much of the prairie pothole region (Hall 1981). It is a predator of duck eggs (Sargeant et al. 1987) and has been implicated in severe predation on duck nests in fields of DNC in east-central North Dakota (Greenwood 1986). Past studies of Franklin's ground squirrels have emphasized natural history (Sowles 1948, Haggerty 1968, Haberman and Fleharty 1971, Iverson and Turner 1972, Murie 1973), but little information is available on their movements and use of habitat. Our objective was to describe the movements and use of habitat by Franklin's ground squirrels on a federally owned WPA where upland habitat was primarily DNC fields of different ages. We thank D. H. Johnson and J. N. Burroughs for help with data processing, R. J. Greenwood, M. A. Sovada, and D. J. Norris for field assistance and helpful suggestions throughout the study, and H. F. Duebbert and D. H. Johnson for comments on manuscript drafts. The study was funded by the U.S. Fish and Wildlife Service, Northern Prairie Wildlife Research Center; the Missouri Cooperative Fish and Wildlife Research Unit; and the Edward K. Love Foundation. The U.S. Fish and Wildlife Service, Missouri Department of Conservation, University of Missouri-Columbia, and the Wildlife Management Institute contribute to the Missouri Cooperative Fish and Wildlife Research Unit. This is Journal Series 10008, Missouri Agricultural Experiment Station Project 189.

Use of Earthen Islands by Nesting Ducks in North Dakota

We studied duck nests on 1 natural island and 21 constructed islands on the J. Clark Salyer National Wildlife Refuge (NWR), North Dakota in 1982-83. We found 286 nests of 7 species; mallard (Anas platyrhynchos), gadwall (A. strepera), and blue-winged teal (A. discors) represented >90% of all nests. The mean annual nest density was 8.7/ha with a mean Mayfield-adjusted nest success of 24%. Islands on which the most ducks were produced were 335-1,085 m offshore, surrounded by 150-200 m of open water, and contained tall, dense, brush or forb cover. Three islands with these characteristics held 37% of the nests and produced 55% of total ducklings. Although gadwalls and mallards formed dense nesting concentrations, bluewinged teal showed little nest-clumping behavior or nest cover preferences. Other factors influencing production rates included a seasonal decline in nest success and between-year variability. To be cost effective, islands located in wetlands with large mink (Mustela vison) and raccoon (Procyon lotor) populations should have adequate spatial isolation and/or predator control. J. WILDL. MANAGE. 53(2):411-417 Recruitment rates of ducks in the intensively farmed portion of the prairie pothole region are low (Cowardin et al. 1983) because of declining habitat and concentration of nest and female duck predators (Sargeant and Arnold 1984). Recent efforts to improve waterfowl production have centered on restricting predator access (e.g., electric fencing) (Lokemoen et al. 1982), cover management (e.g., dense nesting cover [DNC], burning, mowing), and construction or improvement of nesting islands. Some island habitats attract large populations of nesting ducks (Drewien and Fredrickson 1970, Browne et al. 1983) and have high nest success due to the reduced impacts of predators (Duebbert 1966, Vermeer 1968). Artificial islands can potentially produce more ducks/unit area than other habitats, but they are expensive to construct and maintain, and in many areas may not improve nest success enough to justify costs (Lokemoen 1985). Several authors have made recommendations concerning island construction (Hammond and Mann 1956, Duebbert 1982), but only recently have they been tested quantitatively (Giroux 1981, Carlsen 1984). Our objectives were to quantitatively assess selected environmental variables that best explain duck nesting use and production for a group of earthen islands, and to recommend ways to improve waterfowl production on islands. We thank R. A. Stomstad and T. B. Brokke for field assistance. We are grateful to D. Walls for logistic support and personnel to assist with field work. Additional support was provided by the University of North Dakota Biology Department and the Institute for Ecological Studies. Special thanks are extended to R. D. Sayler who provided helpful advice and reviewed the manuscript. The final draft benefited from comments made by R. C. Drewein and H. F. Duebbert. This publication is Contribution 8 of the Institute for Ecological Studies, University of North Dakota.