Search

Mammalian predation is a major cause of mortality for breeding waterfowl in the U.S. Northern Great Plains, and yet we know little about the selection of prairie habitats by predators or how this influences nest success in grassland nesting cover. We selected 2 41.4-km 2 study areas in both 1996 and 1997 in North Dakota, USA, with contrasting compositions of perennial grassland. A study area contained either 15-20% perennial grassland (Low Grassland Composition LGC]) or 45-55% perennial grassland (High Grassland Composition [HGC]). We used radiotelemetry to investigate the selection of 9 landscape cover types by red fox (Vulpes vulpes) and striped skunk (Mephitis mephitis), while simultaneously recording duck nest success within planted cover. The cover types included the edge and core areas of planted cover, wetland edges within planted cover or surrounded by cropland, pastureland, hayland, cropland, roads, and miscellaneous cover types. Striped skunks selected wetland edges surrounded by agriculture over all other cover types in LGC landscapes (P-values for all pairwise comparisons were

We studied mammalian predator activity in relation to patches of grassland habitat in the agricultural landscape of northern Iowa to understand the potential interactions with ground-nesting birds, including waterfowl and ring-necked pheasant (Phasianus colrhicus). We quantified presence and movement direction of striped skunk (Mephitis mephitis), raccoon (Procyon lotor), and red fox (Vulpes vulpes) using unbaited track stations placed along the edges of 100-ha blocks of grassland and at other locations throughout the surrounding landscape. We used logistic regression with repeated measures and Akaike weights to develop predictive models of predator presence as a function of landscape variables including distance from a grassland block, shape of grassland edges, and presence of woodlands, farmsteads, and wetlands. Predators were detected at track stations in the landscape near (≤500 m) grassland blocks 33.5% of the time, more frequently than at stations immediately adjacent to edges of blocks (22.6%), and much more frequently than at stations distant (>500 m) from blocks (13.6%). Striped skunk presence at a station decreased as distance from grassland patches increased and was positively related to the number of farmsteads; raccoon presence was positively related to presence of woody cover; and red fox presence increased with greater area of pastureland and greater isolation from farmsteads, and decreased with increasing amount of strip habitat in the landscape. Predicted predator presence at locations where duck nests were found ≤500 m from blocks of grassland (23.1%) was within 1 SE of the Mayfield nest mortality rate, whereas predicted presence at isolated nest locations (12.0%) was greater than observed nest mortality. Track stations indicated that predators moved into and out of grassland patches at corners of blocks (80% of the time) much more frequently than when they traveled along the straight sides of blocks (7%). If presence of predators is directly related to predation rate, our models predict that risk to nesting birds would be greatest in patches near large grassland blocks where corridors, corners, and smaller patches focus predator activity. We envision that wildlife biologists could use models of predator activity to predict the potential influence of landscape configuration on predation risk to nesting birds.

Wildlife managers in the midwestern United States implicitly recognize that large-scale changes in land use have been a major factor in the nesting ecology of the ring-necked pheasant (Phasianus colchicus), but they have lacked models that quantify the relation between nest success and landscape variables at multiple scales. We used data from 288 nests of radiomarked female pheasants during the 1990-94 breeding seasons in Iowa to study nest-site selection and nest success. We quantified habitat and landscape metrics within the 485-m radius of a home range around nests by using aerial imagery and FRAGSTATS. We screened potential landscape variables by using principal component and classification and regression tree (CART) analyses before developing logistic regression models to predict nest-site selection and success as a function of landscape conditions. A 5-variable logistic regression model incorporating nesting patch size, mean grassland patch size, landscape core area, landscape shape index, and distance to edge predicted nest-site locations at a 77% posterior concordant rate. The CART analyses suggested nest success was best modeled by splitting nest observations into nests in patches ≤15.6 ha and >15.6 ha. For nests in patches ≤15.6 ha, a logistic regression model with site cover type and mean core area index predicted nest success with a 73% posterior concordant rate (P 15.6 ha, a model with site cover type, core area standard deviation, and distance from the nest to the edge predicted nest success best (concordant rate = 64%, P = 0.069), although the effect of distance to edge was very slight (conditional odds ratio = 1.003, 95% CI = 0.997-1.009). Our models suggest managers should strive to provide undisturbed grassland blocks ≥15 ha for nesting pheasants, but our observation was that success was highest in fields 4 times that size. Furthermore, cover in several large grassland blocks within the nesting home range is preferable to concentrating cover in 1 large block. Landscape models like ours could be used to project the consequences of changes in agricultural policy on ring-necked pheasant populations.

Management of ring-necked pheasants (Phasianus colchicus) in agricultura landscapes would be enhanced by knowledge of the relation between survival and habitat composition and configuration. We related survival and habitat use of hen pheasants during spring in Iowa with landscape characteristics in an area of high habitat diversity with 25.0% grasslands and an area of low habitat diversity with 9.3% grassland. Survival of 215 radiomarked hens from 1 April to 3 June 1992-94 averaged 0.81 and did not differ between areas (P = 0.756). Predation was the case of death in 87.5% of the cases, with 66.7% of all deaths attributed to mammals, especially red fox (Vulpes vulpes). Home ranges of 57 hens averaged 36.6 ha in the high diversity area and 47.7 ha in the low diversity area and did not differ between areas (P = 0.603). Density of edge between grassland and other habitat as predictive of the hazard rate, and the odds of mortality increased 2% for every 10 m/ha of additional edge in the home range. Hens with home ranges characterized by small patches of grassland within the cropland matrix survived as well as those with lage blocks of grassland in their home range. Understanding how changes in composition and configuration of landscapes affects wildlife demographics at multiple scales can improve manager's ability to take advantage of agricultural conservation programs.

Survival of chicks is an important and poorly understood component of ring-necked pheasant (Phasianus colchicus) population dynamics. We implanted transmitters in day-old chicks (n = 332) with brooding hens (n = 117) during 1990-94 in northern Iowa and calculated survival to 28 days of age. We contrasted survival among years and between an area in Palo Alto County with >25% grassland habitat and an area in Kossuth County with 85% of the mortality. Twenty-three chicks died of exposure on days when at least a trace of rainfall fell, and 11 of 23 (48%) died on days when rainfall was >0.6 cm (x = 0.96 cm, range = 0.68-3.38 cm). Age of the hen did not influence chick survival. Chick mortality rate was increased by 2.3% for each day chicks hatched after the median date of hatch (15 Jun) and was decreased by 10% for each gram of mass above the average chick mass at hatch (18.5 ± 0.13 g). Habitat management to improve chick survival of pheasants on agricultural landscapes should emphasize perennial grass and legume cover dispersed among crop fields. Grassland cover should remain undisturbed, particularly early in the nesting season (15 Apr-1 Jun), to improve the chances of successful first-nest attempts.

We studied populations of ring-necked pheasant hens (Phasianus colchicus) on a diverse landscape in Palo Alto County, Iowa and on an intensively farmed area in Kossuth County, Iowa to examine the hypothesis that differences in habitat composition influence winter survival. We captured hen pheasants by nightlighting or bait trapping on each site and relocated them with telemetry from December through March, 1989-94. We determined home range area, habitat use, and movements during the day. We estimated survival using Kaplan-Meier statistics and related survival to habitat and weather covariates using parametric models. In both landscapes, home ranges were located in areas with more grass habitat than the surrounding landscape (P < 0.05). Home range area averaged 76 ha and daily movements averaged 251 m at Palo Alto, whereas these variables were 96 ha and 270 m at Kossuth. Survival from 27 November to 1 April ranged from 0.23 in 1993 on Kossuth to 0.96 in 1990 on Palo Alto but the average difference in survival between sites among years was not different from zero (P = 0.77). Parametric hazards models indicated that measures of weather and temperature were predictive of mortality, but that small scale habitat use and daily movements were not. Winters with extensive snow cover and cold temperatures periodically reduce survival even where the distribution of small blocks of cover such as idle grass, woody cover, and wetlands is considered adequate by managers.

We evaluated post-release stratification (after banding) developed by Schwarz et al. (1988) to improve managers' capability to detect and account for heterogeneity in survival among mallards (Anas platyrhynchos) recovered along the upper Mississippi River (UMR). We used band recoveries from 4 banding reference areas in the Prairie Pothole Region spanning 25 years and stratified them by 4 recovery areas in the Central and Mississippi flyways: UMR, UMR-vicinity (UMRV), lower Mississippi River (LMR), and southern plains (SP). We validated the assumption of fidelity to migratory routes and applied post-stratification to estimate recovery and survival rates for mallards recovered in each stratum. Average distance between geographical centers, or centroids, of direct and indirect recoveries was 246.7 km, supporting the assumption of migratory fidelity (P > 0.05). A model with heterogeneous recovery was selected in a majority of tests among strata, due in part to unequal sizes of the 4 recovery strata. However, in most (54.7%) cases survival was estimated to be homogeneous among these strata; only 10.9% of tests among strata rejected (P < 0.05) homogeneous survival in favor of heterogeneous survival. Estimates of homogeneous survival of mallards recovered along the UMR ranged from 52.8% for after-hatch-year (AHY) females banded in southwestern Manitoba to 72.4% for hatch-year (HY) males banded in southwestern Saskatchewan. Survival estimates for the UMR and UMRV recovery strata were not higher (P ≥ 0.06) than estimates from the LMR and SP recovery strata in most cases. Estimated survival was as much as 48.6% less between HY females recovered on the UMR and the LMR, but survival differences averaged 11.1% among all the cases when heterogeneous models were selected. Post-release stratification applied at this regional scale often reduced samples to insufficient size to detect heterogeneity among strata. Biologists should not use evidence provided by this stratified analysis of mallard survival to justify large-scale habitat protection of the UMR.

Biologists need to better understand the effects of harvest on the population dynamics of furbearers. Thus, we used telemetry and Cox's proportional hazards statistics to investigate how habitat factors and harvest regimes were associated with mortality patterns of raccoons (Procyon lotor) in Iowa during 1983-89. Among birth-year (BY) raccoons, greater harvest levels (as estimated by direct recovery rate of ear-tagged animals) were associated with increased hazard, or mortality rate. We found no difference in annual survival among animals >1 year old (after-birth-year, ABY), and changes in hazard rate of ABY raccoons were not associated with greater harvest levels

Small mammal populations were compared on unmined rangeland and reclaimed coal surfacemined land reseeded 2 years and 3-5 years previously. Eight species of small mammals were present on the 3-5-year-old reclaimed areas compared with six on 2-year-old areas and five on unmined rangeland. The masked shrew (Sorex cinereus) and northern grasshopper mouse (Onychomys leucogaster) were captured almost exclusively on 3-5-year-old reclaimed land and unmined rangeland. Deer mice (Peromyscus maniculatus) dominated the community on all reclaimed areas in terms of density (13.8 ? 1.2/ha) and biomass (240.1 ? 109.1 g/ha). They composed 93.6 ? 1.9% of all small mammals captured on 2-year-old areas and 83.2 ? 1.1% of those captured on 3-5-year-old areas. Variation in their density paralleled variations in proportions of juveniles on the recolonized areas. Deer mice also were most abundant on unmined rangeland in terms of density, but thirteen-lined ground squirrels (Spermophilus tridecemlineatus) dominated in terms of biomass. Density of recolonizing deer mice stabilized within 2 years after reclamation. After 2 years, total small mammal density remained relatively constant, and diversity of the community increased. J. WILDL. MANAGE. 48(4):1255-1261 The increase in surface mining for coal in the northern Great Plains has generated interest in the ecological processes of reestablishing plant and animal communities in this region. The role of small mammals in undisturbed grasslands has received attention but little is known from reestablished grasslands. Recolonization by small mammals has been investigated on coal mine spoils in eastern and midwestern regions of the United States where repopulation occurs rapidly (Sly 1976, Hansen and Warnock 1978). Revegetation of land in the Great Plains differs from eastern coal lands because of the semiarid climate, low levels of toxic materials, moderate soil acidity, and advanced reclamation technology (Holechek 1982). The objective of this study was to compare community composition and density of small mammals on reclaimed areas of different ages after soil replacement and reseeding. Information from this study was used in an evaluation of the impact of grazing by small mammals on revegetated land (Hingtgen 1982). This research was supported by the USDA For. Serv., Rocky Mt. For. and Range Stn., Res. Work Unit in Rapid City, the AMAX Coal Co., and the USDI Bur. of Mines, under grant G1106002. Any opinions, findings, and conclusions or recommendations expressed in this publication do not necessarily reflect the views of the Bur. of Mines, Dep. of the Inter. We thank R. R. Shinn of AMAX for cooperation during initial phases of the project and acknowledge D. G. Steward, C. H. Sieg, and D. W. Uresk for reviews of the manuscript.

We describe a simulation model that estimates the energy and protein demand, body weight fluctuations, and population density changes of black-tailed jack rabbits (Lepus californicus), and tests the hypothesis that dense populations are limited by forage resources. Using field and literature values for energy and nitrogen requirements for maintenance, growth, and reproduction, we estimated the demand for forage resources by fluctuating jack rabbit populations in Curlew Valley, Utah. The model produced body weight dynamics within error estimates of measured body weights of both sexes for 90% of an annual cycle. Simulated daily energy requirements (161.2 kcal/kg/day) and daily nitrogen requirements (353.6 mg/kg/day) were within 10% of reported empirical values. Sensitivity analysis of model parameters and variables suggests that output is most sensitive to variations in such inputs as digestive efficiency and maximum consumption rate. Simulated populations, at peak densities, consumed < 1% of available forage resources and there was no significant difference at different population levels in simulated energy or protein difference state. We conclude that the observed declines from population peaks, characteristic of this oscillatory population, must be caused by ecological mechanisms other than food resource depletion. J. WILDL. MANAGE. 46(4):1018-1035 Efforts to document and understand the population dynamics of consumers in ecosystems often have been founded upon demographic analyses of population changes. Competing explanations for population fluctuations of mammalian consumers have included both extrinsic and intrinsic mechanisms (see Lidicker 1978 for review). Population dynamics of a species may be related to many variables and dependent upon local conditions so that determining the ecological mechanisms causing population change is difficult. The problems are particularly difficult for medium-sized, free-ranging herbivores such as black-tailed jack rabbits where measurements of factors limiting population size are frequently limited by difficulties in isolating causal factors in the field. Black-tailed jack rabbit populations are known to fluctuate widely over much of the species' range. As a result of demographic studies of jack rabbits in Curlew Valley, northern Utah, Gross et al. (1974) concluded that these changes are of an oscillatory form. Density of jack rabbits in Curlew Valley has changed from 0.12 to 1.02 rabbits/ha, during a single fluctuation. Wagner and Stoddart (1972) showed that coyote (Canis latrans) predation influenced the oscillations in large part. H wever, because jack rabbits increase faster than coyotes, predation mortality is nversely density-dependent. Jack rabbits may be released from predation as the major source of mortality during popu ation increases. "Other mortality sources--disease, exhaustion of the food supply or pituitary-adrenal stress, or both-will presumably be needed to reverse the population trend, induce the decline, and enable the now-abundant coyotes once again to assume dominance over the prey" (Wagner and Stoddart 1972:341). Periodic food depletion has been suggested as an ecological mechanism that limits population size of many vertebrates (Lack 1954), including brown lemmings (Lemmus sibiricus) (Thompson 1955, Pitelka 1957, Collier et al. 1975), I Present address: Department of Animal Ecology, Iowa State University, Ames, IA 50011. 1018 J. Wildl. Manage. 46(4):1982 This content downloaded from 157.55.39.116 on Sun, 18 Sep 2016 06:26:10 UTC All use subject to http://about.jstor.org/terms SIMULATION OF JACK RABBIT NUTRITION* Clark and Innis 1019 wood-pigeons (Columba palumbus) (Murton et al. 1966), red grouse (Lagopus lagopus scoticus) (Miller et al. 1970, Watson and Moss 1971), and snowshoe hares (Lepus americanus) (Keith 1974). Keith (1974), Keith and Windberg (1978), Pease et al. (1979), and Vaughan and Keith (1981) concluded that food shortage initiates population declines of snowshoe hares. They observed a pattern of "higher winter-spring weight loss, decreased reproduction, decreased juvenile growth rate and decreased juvenile survival over winter" (Pease et al. 1979:58) that preceded the peak density and slowed the rate of increase of the population. The objective of our study was to examine a similar hypothesis regarding the role of forage availability in determining population change in black-tailed jack rabbits. Such a hypothesis involves complex dynamic relationships between forage availability and jack rabbit demographics. A simulation modeling approach is ideally suited for coping with the complexity and dynamic characteristics of such systems and identifies important relationships and weaknesses in the data (Forrester 1961, Wiens and Innis 1974). Portions of this study were supported by grants from the National Science Foundation (BMS-7420000) to G. S. Innis, the US/IBP Desert Biome (GB-15886) to F. H. Wagner, and the Energy and Research and Development Administration (E11-1-1329) to L. C. Stoddart. This work could not have been accomplished without the cooperation of L. C. Stoddart who provided access to unpublished data. We also thank R. B. Frederick, E. E. Klaas, W. P. Porter, and F. H. Wagner for reviewing a version of this manuscript.

Muskrats (Ondatra zibethicus) were marked from 1981 through 1984 and recovered for 5 years in Pool 9, Upper Mississippi River to determine survival and harvest rates by using banding methodology. Tag reporting rate, estimated from trapper interviews, averaged 83 ? 1% and was constant among years. Survival and recovery rates did not vary significantly between sexes but were significantly different between birth-year (BY) and after-birth-year (ABY) animals. Data best fit a model assuming constant age-specific survival and year-specific recovery rates. Constant annual survival rate of BY animals was 15.7 ? 2.3%, whereas survival of ABY animals was 5.8 ? 1.5%. Harvest rates ranged from 17% in 1982 to 45% in 1981, and averaged 32 ? 2% of the fall population in all years and habitats combined. Maximum sustained yield in backwaters was 20% of yield in openwaters although annual survival was not different between habitats. There was a density-dependent increase in nonharvest, birth-to-trapping season survival of juveniles, which compensated for increases in harvest mortality. J. WILDL. MANAGE. 51(2):265-272 The effects of exploitation on populations of vertebrates remains one of the important theoretical and applied questions in wildlife ecology. Originally, basic theory on the intercompensatory nature of mortality factors emerged from studies by Errington (1946, 1956, 1963) on the effects of natural predation in influencing abundance of prey species, particularly muskrats. His concepts on predation were extended to include effects of harvest on populations as a basis for game management (Allen 1954, Hickey 1955). Wagner (1969:269) later concluded that the evidence that "game populations can exist under heavy hunting pressure without obvious effects on their density" was equivocal. Much recent research and discussion has focussed on migratory waterfowl (Anderson and Burnham 1976, Burnham and Anderson 1984, Nichols et al. 1984). Anderson and Burnham (1976:5-9) examined the effect of harvest on annual survival of mallards (Anas platyrhynchos) and defined the competing hypotheses of "compensatory to a threshold point" and "totally additive," which form the basis for much of this paper. Despite the interest and importance of the effects of harvest on survival, details about mechanisms involved in the relationship between exploitation and population dynamics are poorly known. Therefore, in 1981, I began studies on muskrats on the Upper Mississippi River Fish and Wildlife Refuge (UMRFWR) to examine population responses to exploitation. Muskrats are an ideal study species because: large samples of muskrats are easily captured and marked, population densities vary substantially (Clay and Clark 1985), harvest effort varies in response to changes in trapping conditions (Clark 1986), and they provide a contrast to the studies on migratory waterfowl. Furthermore, practical management of muskrats rests on whether populations respond to changes in harvest in an inversity-compensatory manne (sensu Roseberry [1979]). Clay and Clark (1985) have previously shown density-dependent reproduction (inversity) in Pool 9 populations of muskrats. The task of demonstrating whether compensatory interactions exist between natural mortality and harvest remains. In this paper I examine the effects of harvest on survival, with the goal of contributing to both the theoretical basis for harvesting populations and the management of muskrats. A series of consequences of compensatory theory (Nichols et al. 1984) was examined in light of the Pool 9 studies. These results are an extension and, to some degree, a re-examination of previous results (Clay and Clark 1985) using more data and new techniques. The field work was funded through the Iowa Coop. Wildl. Res. Unit by the Upper Miss. River Basin Comm., U.S. Fish and Wildl. Serv., Iowa Conserv. Comm., and Wis. Dep. Nat. Resour. This is Paper J-12181 of the Iowa Agric. and Home Econ. Exp. Stn., Proj. 2401. R. T. Clay, K. L. Johnson, R. J. Munkel, K. R. Utterson, and R. E. Young conducted the marking and M. M. Anderson and J. Lyons facilitated tag recovery and contact with trappers. J. D. Nichols was particularly helpful with suggestions on parameter and variance estimation and interpretation. K. J. Koehler and H. D. Baker

Measurements of natality rates, survival rates, movements, and densities were integrated to describe the mechanics of population balance for snowshoe hares (Lepus americanus) in Colorado (1969-71) and Utah (1972-73), near the southern extreme of this species' range. Adult home-range size averaged eight hectares in spruce (Picea spp.)-fir (Abies spp.) forest, the preferred habitat. Juveniles used unforested habitat more frequently than adults. Population density remained stable throughout the duration of both studies; historical accounts also indicate population densities have remained fairly stable in the Rocky Mountain region. Hares commenced breeding from mid-April to mid-May. Females surviving an entire reproductive season produced an average of 2.1-2.3 litters annually. Later-litter sizes, averaging 4.8 in Colorado and 5.9 in Utah, were larger than most litter sizes reported from higher latitudes. The annual natality rate was 8.2 and 11.5 young per female surviving an entire reproductive season in Colorado and Utah, respectively. Annual survival rate for adults in Colorado was 0.45. About 16 percent of juveniles born each summer needed to survive until the following breeding season to balance the population density. Second-litter juveniles had a lower survival rate than did first-litter juveniles. We surmise the long-term stability of the hare population in the Rocky Mountains to be related to dispersal of juveniles into poor (open) habitats where survival is low. The discontinuity of preferred spruce-fir habitat allows dispersal into open habitat to occur readily, and this may be the main mechanism averting the potential population increase. J. WILDL. MANAGE. 39(3):535-549 The snowshoe hare is indigenous to boreal forests throughout North America. This species has long interested population ecologists because of its "cyclic" population fluctuations (Keith 1963); however, mechanisms of population regulation are still poorly understood. In particular, little is known about population characteristics of hares in the southernmost extension of its range in the Rocky and Appalachian Mountains in the United States. This paper helps fill this void by presenting information on the population ecology of snowshoe hares in the Rocky Mountains of central Colorado (1969-71) and northern Utah (197273). The study had three objectives: (1) to estimate local densities of snowshoe hares, (2) to examine natality rates, survival rates, and movements, and to describe the immediate mechanics of population balance and fluctuation, and (3) to compare these populat on parameters with those published from snowshoe hare studies conducted at higher latitudes in an effort to clarify mechanisms causing cyclic fluctuations. We gratefully acknowledge J. E. Gross and M. L. Wolfe for their guidance and interest. D. A. Hein, F. H. Wagner, F. A. Glover, H. S. Donoho, S. Dolbeer, and M. Laderach also provided timely assistance.

This paper analyzes the impact of small-mammal activity on the standing crop of vegetation on areas reclaimed after coal stripmining in northeastern Wyoming. The small-mammal community included 2 carnivorous, 2 herbivorous, and 4 omnivorous species. Deer mine (Peromysucs maniculatus ) dominated the population on all areas, constituting 85.4% of small mammals live-trapped. Plant species preferred as food by deer mice included sainfoin (Onobrychis viciaefolia), fireweed summercypress, (Kochia scoparia), and fourwing saltbush (Atriplex canescens). Grasses had lower preference rankings than forbs. The deer mouse population consumed 20 g/ha/day of plant matter. They consumed 0.11% of the aboveground peak standing crop (PSC) during the growing season, and the consumption of the total small-mammal community was less than 1% of PSC. However, the PSC of sainfoin was significantly affected by grazing of small-mammal populations. Large tracts of land in the shortgrass prairie of the Northern Great Plains have been strip-mined for coal and require reclamation to levels of productivity that existed before the disturbance. Understanding the role of plant-animal interactions in the reestablishment of vegetation after reclamation is essential to designing successful reclamation procedures for strip-mined land. Small Mammals can limit the effectiveness of seedings on rangeland (Nelson et al. 1970), burned brushlands (Howard 1950), and disrupted forest habitat (Radvanyi 1980. Grazing by small mammals specifically has been found to decrease primary production in arctic tundra (Batzli 1975) and desert scrub (Soholt 1973) and the