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Results for “Journal of Wildlife Management”

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At least 1,171 records · Page 65Linked to original sources
USGS1999

Environmental characteristics associated with the occurrence of avian botulism in wetlands of a northern California refuge

Avian botulism is an important disease affecting many species of waterbirds in North America, but the environmental conditions that initiate outbreaks are poorly understood. To determine wetland attributes associated with outbreaks of avian botulism in waterbirds at the Sacramento National Wildlife Refuge (SNWR), California, we compared environmental characteristics between wetlands where outbreaks occurred (outbreak wetlands) and did not occur (nonoutbreak wetlands). In June through October, 1987 89, we monitored the occurrence of avian botulism via observations for sick or dead sentinel mallards (Anas platyrhynchos) placed in 4 wetland enclosures. During this same time period, we collected environmental data from the water column and sediments of each wetland enclosure at 10 14-day sampling intervals. Multivariate analysis was used to reduce 22 environmental variables to 7 factors for inclusion in subsequent statistical analyses. We found that outbreak wetlands had significantly lower redox potential than nonoutbreak wetlands. The probability of botulism in sentinel mallards was associated with increasing temperature, increasing invertebrate abundance or biomass, and decreasing turbidity. However, because these factors were not consistently higher in outbreak wetlands compared to nonoutbreak wetlands, they may have a more proximate effect in initiating an outbreak.

California↗
USGS1998

Settlement rate of lead shot in tundra wetlands

Several species of breeding waterfowl have been shown to be exposed to lead shot on the Yukon-Kuskokwim (Y-K) Delta, Alaska. I 'seeded' experimental plots with number 4 lead shot to determine the settlement rate of shot in wetland types commonly used by foraging waterfowl. I resampled plots for 3 years, using a suction dredge to remove sediment in 4-cm layers. There was no consistent change in the proportion of shot recovered in the 0-4-cm layer among years or habitat types. My results suggest lead shot is available to feeding waterfowl for many years, and that exposure of waterfowl to lead poisoning will likely occur for >3 years after the use of lead shot is curtailed.

Alaska↗
USGS1998

A model of northern pintail productivity and population growth rate

Our objective was to synthesize individual components of reproductive ecology into a single estimate of productivity and to assess the relative effects of survival and productivity on population dynamics. We used information on nesting ecology, renesting potential, and duckling survival of northern pintails ( Anas acuta ) collected on the Yukon-Kuskokwim Delta (Y-K Delta), Alaska, 1991-95, to model the number of ducklings produced under a range of nest success and duckling survival probabilities. Using average values of 25% nest success, 11% duckling survival, and 56% renesting probability from our study population, we calculated that all young in our population were produced by 13% of the breeding females, and that early-nesting females produced more young than later-nesting females. Further, we calculated, on average, that each female produced only 0.16 young females/nesting season. We combined these results with estimates of first-year and adult survival to examine the growth rate (X) of the population and the relative contributions of these demographic parameters to that growth rate. Contrary to aerial survey data, the population projection model suggests our study population is declining rapidly (X = 0.6969). The relative effects on population growth rate were 0.1175 for reproductive success, 0.1175 for first-year survival, and 0.8825 for adult survival. Adult survival had the greatest influence on X for our population, and this conclusion was robust over a range of survival and productivity estimates. Given published estimates of annual survival for adult females (61%), our model suggested nest success and duckling survival need to increase to approximately 40% to achieve population stability. We discuss reasons for the apparent discrepancy in population trends between our model and aerial surveys in terms of bias in productivity and survival estimates.

Alaska↗
USGS1998

Dabbling duck behavior and aircraft activity in coastal North Carolina

Requests to increase military aircraft activity in some training facilities in the United States have prompted the need to determine if waterfowl and other wildlife are adversely affected by aircraft disturbance. We quantified behavioral responses of wintering American black ducks (Anas rubripes), American wigeon (A. americana), gadwall (A. strepera), and American green-winged teal (A. crecca carolinensis) exposed to low-level flying military aircrafts at Piney and Cedar islands, North Carolina, in 1991 and 1992. Waterfowl spent ≥1.4% of their time responding to aircraft, which included flying, swimming, and alert behaviors. Mean duration of responses by species ranged from 10 to 40 sec. Costs to each species were deemed low because disruptions represented a low percentage of their time-activity budgets, only a small proportion of birds reacted to disturbance (13/672; 2%), and the likelihood of resuming the activity disrupted by an aircraft disturbance event was high (64%). Recorded levels of aircraft disturbance (i.e., x̄ = 85.1 dBA) were not adversely affecting the time-activity budgets of selected waterfowl species wintering at Piney and Cedar islands.

Journal of Wildlife Management↗
USGS1998

Do black ducks and wood ducks habituate to aircraft disturbance?

Requests to increase military aircraft activity in some training facilities in the United States have raised the need to determine if waterfowl and other wildlife are adversely affected by aircraft disturbance. We hypothesized that habituation was a possible proximate factor influencing the low proportion of free-ranging ducks reacting to military aircraft activities in a training range in coastal North Carolina during winters 1991 and 1992. To test this hypothesis, we subjected captive, wild-strain American black ducks (Anas rubripes) and wood ducks (Aix sponsa) to actual and simulated activities of jet aircraft. In the first experiment, we placed black ducks in an enclosure near the center of aircraft activities on Piney Island, a military aircraft target range in coastal North Carolina. The proportion of times black ducks reacted (e.g., alert posture, fleeing response) to visual and auditory aircraft activity decreased from 38 to 6% during the first 17 days of confinement. Response rates remained stable at 5.8% thereafter. In the second experiment, black ducks and wood ducks were exposed to 6 different recordings of jet noise. The proportion of times black ducks reacted to noise decreased (P < 0.05) from first day of exposure (25%) to last (i.e., day 4; 8%). Except for a 2% difference in comfort, we detected no differences (P > 0.05) in time-activity budgets of black ducks between pre-exposure to noise and 24 hr after first exposure. Unlike black ducks, wood duck responses to jet noise did not decrease uniformly among experimental groups following initial exposure to noise (P = 0.01). We conclude that initial exposure to aircraft noise elicits behavioral responses from black ducks and wood ducks. With continued exposure of aircraft noise, black ducks may become habituated. However, wood ducks did not exhibit the same pattern of response, suggesting that the ability of waterfowl to habituate to aircraft noise may be species specific.

Journal of Wildlife Management↗
USGS1997

Statistical power analysis in wildlife research

Statistical power analysis can be used to increase the efficiency of research efforts and to clarify research results. Power analysis is most valuable in the design or planning phases of research efforts. Such prospective (a priori) power analyses can be used to guide research design and to estimate the number of samples necessary to achieve a high probability of detecting biologically significant effects. Retrospective (a posteriori) power analysis has been advocated as a method to increase information about hypothesis tests that were not rejected. However, estimating power for tests of null hypotheses that were not rejected with the effect size observed in the study is incorrect; these power estimates will always be ≤ 0.50 when bias adjusted and have no relation to true power. Therefore, retrospective power estimates based on the observed effect size for hypothesis tests that were not rejected are misleading; retrospective power estimates are only meaningful when based on effect sizes other than the observed effect size, such as those effect sizes hypothesized to be biologically significant. Retrospective power analysis can be used effectively to estimate the number of samples or effect size that would have been necessary for a completed study to have rejected a specific null hypothesis. Simply presenting confidence intervals can provide additional information about null hypotheses that were not rejected, including information about the size of the true effect and whether or not there is adequate evidence to 'accept' a null hypothesis as true. We suggest that (1) statistical power analyses be routinely incorporated into research planning efforts to increase their efficiency, (2) confidence intervals be used in lieu of retrospective power analyses for null hypotheses that were not rejected to assess the likely size of the true effect, (3) minimum biologically significant effect sizes be used for all power analyses, and (4) if retrospective power estimates are to be reported, then the α -level, effect sizes, and sample sizes used in calculations must also be reported.

Journal of Wildlife Management↗
USGS1997

Comparison of tree basal area and canopy cover in habitat models: Subalpine forest

Canopy cover and basal area are 2 common measures of tree cover used in forest wildlife habitat models and resource selection studies. When choosing between these 2 measures, it is important to recognize that they may differentially estimate relative cover of coexisting tree species due to differences in bole diameter distributions, crown overlap, and crown widths as a function of bole diameter. I found moderate agreement (multivariate p = 0.62, P < 0.0001) between lodgepole pine (Pinus contorta), Engelmann spruce (Picea engelmannii), and subalpine fir (Abies lasiocarpa) composition estimated by relative canopy cover and relative basal area in young to old-growth stands (n = 31) in subalpine forest of northcentral Colorado. However, differences between stand compositions estimated by relative canopy cover and relative basal area (average = 17%, range = 1-44%) were predictable based on multiple regression models of canopy cover as a function of basal area and trees/ha. I attributed most (11 of 14) above average deviations (>17%) to differences in diameter distributions among species in mature to old-growth (>200 yr) stands. Low densities of large diameter lodgepole pine or Engelmann spruce were a greater proportion of the basal area than of the canopy cover, while the converse occurred for higher densities of small and large diameter subalpine fir. Only 3 of 14 deviations >17% were attributed to species differences in crown overlap and crown width as a function of bole diameter, which occurred for young (22 yr) and intermediate-aged (48-80 yr) stands. I recommend use of basal area rather than canopy cover to estimate tree cover when it is desirable to emphasize large, uncommon trees that are resources used by the wildlife species of interest or that are indicators of important forest disturbance and successional conditions.

Journal of Wildlife Management↗
USGS1999

Mate loss in winter and mallard reproduction

Mallards (Anas platyrhynchos) frequently pair during winter, and duck hunting seasons have been extended until the end of January in several southern states in the Mississippi Flyway. Therefore, we simulated dissolution of pair bonds from natural or hunting mortality by removing mates of wild-strain, captive, yearling female mallards in late January 1996 and early February 1997 to test if mate loss in winter would affect subsequent pair formation and reproductive performance. Most (97%) widowed females paired again. Nesting and incubation frequencies, nest-initiation date, days between first and second nests, and egg mass did not differ (P > 0.126) between widowed and control (i.e., no mate loss experienced) females in 1996 and 1997. In 1997, widowed females laid 1.91 fewer eggs in first nests (P = 0.014) and 3.75 fewer viable eggs in second nests (P = 0.056). Computer simulations with a mallard productivity model (incorporating default parameters [i.e., average environmental conditions]) indicated that the observed decreased clutch size of first nests, fewer viable eggs in second nests, and these factors combined had potential to decrease recruitment rates of yearling female mallards 9%, 12%, and 20%. Our results indicate that winter mate loss could reduce reproductive performance by yearling female mallards in some years. We suggest caution regarding extending duck hunting seasons in winter without concurrent evaluations of harvest and demographics of mallard and other duck populations.

Journal of Wildlife Management↗
USGS2003

True metabolizable energy for wood ducks from acorns compared to other waterfowl foods

Acorns of bottomland red oaks (Quercus spp.) are an important food of North American wood ducks (Aix sponsa). Barras et al. (1996) demonstrated that female wood ducks selected willow oak (Q. phellos) acorns over other species. We measured true metabolizable energy (TME) derived by captive, wild-strain, adult female wood ducks from acorns of willow oak, water oak (Q. nigra), cherrybark oak (Q. pagoda), and pin oak (Q. palustris) to determine whether female wood ducks ' preference for willow oak acorns was related to TME. Estimates of TME within acorn species were relatively precise, yet we did not detect variation in TME among acorn species (P=0.31); hence, we estimated TME across species (2.76±0.033 [SE] kcal/g dry mass; n=34). We concluded that TME apparently did not explain female wood ducks ' preference for willow oak acorns and hypothesized that morphological characteristics of willow oak acorns may be proximate cues related to selection by wood ducks . We also summarized known TME estimates for acorns fed to wood ducks and mallards (Anas platyrhynchos), and natural and agricultural foods fed to mallards, northern pintails (A. acuta), blue-winged teal (A. discors), and Canada geese (Branta canadensis). We found that acorns and moist-soil plant seeds and tubers provided, on average, about 76% of the TME in agricultural seeds. Thus, bottomland-hardwood and moist-soil habitats have potential to provide significant amounts of dietary energy , as well as greater diversity of foods and nutrients than croplands. Researchers should continue to determine TME of common foods (plant and animal) of waterfowl , and use TME in estimating waterfowl habitat carrying capacity (e.g., Reinecke et al. 1989). Additionally, large-scale, reliable estimates of plant and animal food availability in bottomland-hardwood and moist-soil habitats are needed to evaluate carrying capacity of landscapes important to waterfowl , such as the Mississippi Alluvial Valley (MAV).

Journal of Wildlife Management↗
USGS2003

Short-term bird response to harvesting switchgrass for biomass in Iowa

The Conservation Reserve Program (CRP) provides habitat for grassland birds, but as contracts expire, some CRP fields might be returned to rowcrop production. One alternative to returning CRP fields to rowcrops is to produce switchgrass ( Panicum virgatum ) for use as a biomass fuel. Because the biomass is harvested during the fall and winter, breeding birds would not be directly affected by mowing the fields bur might be influenced by changes in vegetation structure resulting from the harvest. We evaluated bird abundances and nest success in totally harvested, partially harvested (alternating cut and uncut strips), and nonharvested CRP switchgrass fields in southern Iowa, USA, in 1999 and 2000. Species richness did not differ among harvest treatments. Abundances of most species (16 of 18) were not affected by the harvesting of switchgrass fields, and strip width did not affect bird numbers in strip-harvested fields. Grasshopper sparrows ( Ammodramus savannarum ) were more abundant in harvested portions of fields, and more sedge wrens ( Cistothorus platensis ) were recorded in nonharvested areas. The residual vegetation in nonharvested areas provided nest cover for species that begin nesting early in the season (e.g., northern harrier [Circus cyaneus] and ring-necked pheasant [ Phasianus colchicus ]). Nest success rates of grasshopper sparrows and common yellowthroats ( Geothlypis trichas ) were similar to those reported by other studies in switchgrass fields and might be sufficient to maintain stable populations. In general, switchgrass biomass fields create breeding habitat for some grassland birds, and a mixture of harvested and nonharvested fields would be more beneficial to grassland birds than totally harvesting or partially harvesting all switchgrass fields.

Iowa↗
USGS2000

Accuracy and precision of estimating age of gray wolves by tooth wear

We evaluated the accuracy and precision of tooth wear for aging gray wolves ( Canis lupus ) from Alaska, Minnesota, and Ontario based on 47 known-age or known-minimum-age skulls. Estimates of age using tooth wear and a commercial cementum annuli-aging service were useful for wolves up to 14 years old. The precision of estimates from cementum annuli was greater than estimates from tooth wear, but tooth wear estimates are more applicable in the field. We tended to overestimate age by 1-2 years and occasionally by 3 or 4 years. The commercial service aged young wolves with cementum annuli to within ± 1 year of actual age, but under estimated ages of wolves ≥ 9 years old by 1-3 years. No differences were detected in tooth wear patterns for wild wolves from Alaska, Minnesota, and Ontario, nor between captive and wild wolves. Tooth wear was not appropriate for aging wolves with an underbite that prevented normal wear or severely broken and missing teeth.

Alaska↗
USGS2000

Nest predation on black-tailed prairie dog colonies

Nest predation is the principal cause of mortality for many grassland birds. Predation rates may be higher on prairie dog colonies because they may have less available nesting cover and may increase predator abundance. We compared 14-day nest predation rates for 1,764 artificial nests on 102 black-tailed prairie dog ( Cynomys ludovicianus ) colonies and their paired off-colony sites (similar habitat lacking prairie dogs) from 14 May to 26 June 1998 in South Dakota and Wyoming. Predation rates on colonies (66.2 ± 2.2%; x̄ ± SE) were 29.5% higher than at off-colony sites (51.1 ± 2.7%). Nesting cover on colonies was less dense and more uniform in structure and regression analysis showed differences in nest predation rates were correlated with estimates of mean nesting cover. Avian species associated with prairie dog colonies had smaller clutches and more broods/year than species associated with off-colony sites, suggesting a mechanism that may help compensate for increased risk of nest failure. Factors that influence predator-prey dynamics (e.g., habitat fragmentation) or foraging success (e.g., insect availability) also may help explain higher risk of nest predation on prairie dog colonies. Our conclusions support others in recommending protection of large, intact prairie dog ecosystems.

Colorado, South Dakota, Utah, Wyoming↗
USGS2000

Relationships of habitat patch size to predator community and survival of duck nests

We studied duck nest success and predator community composition in relation to size of discrete patches of nesting cover in the Prairie Pothole Region (PPR) of the United States in 1993-95. We focused on nests in uplands that were seeded to perennial grasses and forbs and enrolled in the Conservation Reserve Program (CRP) in Minnesota, North Dakota, and South Dakota. We estimated daily survival rates (DSRs) of upland duck nests and indices of activity for red foxes (Vulpes vulpes), coyotes (Canis latrans), American badgers (Taxidea taxus), striped skunks (Mephitis mephitis), and Franklin's ground squirrels (Spermophilus franklinii), and related these variables to habitat patch size. The effect of patch size (small vs. large) on estimated annual mean DSR was dependent on date of nest initiation (early vs. late) and year. Examination of within-year comparisons for early and late nests suggested that DSR was generally greater in larger habitat patches. Activity indices for the 5 mammalian nest predators were influenced differently by year, location, and patch size. Activity indices of the red fox were greatest in small patches. Coyote indices were the most inconsistent, demonstrating a year X location X patch size interaction. Activity indices of the striped skunk and American badger varied only among years. Franklin's ground squirrel indices were affected by study area location, with higher indices in the southeast than the northwest. Red fox activity was weakly correlated with that of the striped skunk and coyote. Although a positive relationship between habitat patch size and nest success probably exists, we believe the experiment to fully test this hypothesis will continue to be elusive.

Journal of Wildlife Management↗
USGS2000

Winter survival of adult female harlequin ducks in relation to history of contamination by the Exxon Valdez oil spill

Harlequin duck ( Histrionicus histrionicus ) life-history characteristics make their populations particularly vulnerable to perturbations during nonbreeding periods. The 1989 Exxon Valdez oil spill was a major perturbation to nonbreeding habitats of harlequin ducks in Prince William Sound, Alaska, which resulted in population injury. To assess the status of population recovery from the oil spill and to evaluate factors potentially constraining full recovery, we used radiotelemetry to examine survival of adult female harlequin ducks during winters of 1995-96, 1996-97, and 1997-98. We implanted 294 harlequin ducks (154 and 140 in oiled and unoiled areas, respectively) with transmitters and tracked their signals from aircraft during October through March. We examined variation in survival rates relative to area and season (early, mid, and late winter) through comparisons of models using Akaike's information criterion (AIC(c)) values. The 3 models best supported by the data indicated that survival of birds in oiled areas was lower than in unoiled areas. Inclusion of standardized body mass during wing molt in the 3 best models did not improve their fit, indicating that body mass during wing molt did not affect subsequent winter survival. In the model that best fit our data, survival was high in early winter for both areas, lower during mid and late winter seasons, and lowest in oiled areas during mid winter. Cumulative winter survival estimated from this model was 78.0% (SE = 3.3%) in oiled areas and 83.7% (SE = 2.9%) in unoiled areas. We determined that area differences in survival were more likely related to oiling history than intrinsic geographic differences. Based on a demographic model, area differences in survival offer a likely mechanism for observed declines in populations on oiled areas. Concurrent studies indicated that harlequin ducks continued to be exposed to residual Exxon Valdez oil as much as 9 years after the spill. We suggest that oil exposure, mortality, and population dynamics were linked and conclude that continued effects of the oil spill likely restricted recovery of harlequin duck populations through at least 1998.

Alaska↗
USGS2003

Sampling designs for carnivore scent-station surveys

Scent stations usually are deployed in clusters to expedite data collection and increase the number of stations that can be operated for a given cost. Presumed benefits of cluster sampling may not be realized, however, unless cluster sizes are chosen with respect to sampling variation within and among clusters. To encourage and facilitate the use of efficient designs and reporting standards, we used data collected in Minnesota, USA, during 1986-1991 to (1) compare the performance of survey designs with various numbers of stations/cluster; (2) estimate relations between required sample sizes and visitation rates, changes in visitation rates, and error rates; and (3) compare 2 measures of carnivore response: proportions of scent stations ( station index) and proportions of clusters (line index) visited by red foxes (Vulpes vulpes) and striped skunks (Mephitis mephitis). Despite broad ecological differences between the species, results were similar for foxes and skunks. Foxes visited 2-21% of stations and 15-84% of lines. Skunks visited 1-16% of stations and 3-54% of lines. Station and line indices were closely related (r 2 > 0.86) and were similarly sensitive indicators of change in visitation rates. Low visitation rates greatly limited the potential usefulness of scent - station surveys because required minimum sample sizes increased exponentially as visitation rates decreased. For visitation rates below 5-10%, required minimum sample sizes were very large and difficult to anticipate. Relative to single-stage sampling , cluster sampling with 10 stations/cluster inflated sample variances, hence sample sizes required to achieve a fixed level of precision, by a factor of 1.6-2.2. Cluster sampling is advantageous only when cost savings permit increases in sample sizes that outweigh concomitant increases in sampling variability. Costs and sampling variation both should be considered when choosing survey designs , and designs should be evaluated and refined as data accumulate.

Minnesota↗
USGS2003

Habitat use and movements of repatriated Wyoming toads

We studied habitat use and movements of a repatriated population of federally endangered Wyoming toads (Bufo baxteri) after the breeding season at Mortenson Lake, Albany County, Wyoming , USA. We followed 8 adult toads using telemetry (n = 68 relocations) during periods of activity and observed 59 post-metamorphic juvenile toads (n = 59 locations). Adult toads used habitat with a greater mean vegetation canopy cover (mean = 52.6%) than juveniles (mean = 39.20%). We found adults farther from the shoreline (mean = 1.32 m) than juveniles (mean = 1.04 m). Substrates used by toads had a mean surface temperature of 20.31°C for adults and 23.05°C for juveniles. We found most adult and juvenile toads on saturated substrates. All adult toads sampled did not move outside of a 30 x 500 m area along the east-to-south shore where they were captured. Toads were active diurnally through the end of October. We found toads torpid at night. We compared our results to a similar study of the historic population and found that adult toads of the current population used denser vegetation than those of the historic population. Unlike many bufonids, terrestrial stages of the Wyoming toad appear to depend on saturated substrates. The best logistic regression predictors of adult and juvenile toad presence were surface temperature and distance to shore. Survey transects within the moist margin of the lake (≤10 m from water) and after substrates have reached temperatures ≥20°C will likely yield more detections.

Wyoming↗