Wildlife Monographs最新文献

Populations of Pacific common eiders (Somateria mollissima v-nigrum) on the Yukon-Kuskokwim Delta (YKD) in western Alaska declined by 50–90% from 1957 to 1992 and then stabilized at reduced numbers from the early 1990s to the present. We investigated the underlying processes affecting their population dynamics by collection and analysis of demographic data from Pacific common eiders at 3 sites on the YKD (1991–2004) for 29 site-years. We examined variation in components of reproduction, tested hypotheses about the influence of specific ecological factors on life-history variables, and investigated their relative contributions to local population dynamics. Reproductive output was low and variable, both within and among individuals, whereas apparent survival of adult females was high and relatively invariant (0.89 ± 0.005). All reproductive parameters varied across study sites and years. Clutch initiation dates ranged from 4 May to 28 June, with peak (modal) initiation occurring on 26 May. Females at an island study site consistently initiated clutches 3–5 days earlier in each year than those on 2 mainland sites. Population variance in nest initiation date was negatively related to the peak, suggesting increased synchrony in years of delayed initiation. On average, total clutch size (laid) ranged from 4.8 to 6.6 eggs, and declined with date of nest initiation. After accounting for partial predation and non-viability of eggs, average clutch size at hatch ranged from 2.0 to 5.8 eggs. Within seasons, daily survival probability (DSP) of nests was lowest during egg-laying and late-initiation dates. Estimated nest survival varied considerably across sites and years (mean = 0.55, range: 0.06–0.92), but process variance in nest survival was relatively low (0.02, CI: 0.01–0.05), indicating that most variance was likely attributed to sampling error. We found evidence that observer effects may have reduced overall nest survival by 0.0–0.36 across site-years. Study sites with lower sample sizes and more frequent visitations appeared to experience greater observer effects. In general, Pacific common eiders exhibited high spatio-temporal variance in reproductive components. Larger clutch sizes and high nest survival at early initiation dates suggested directional selection favoring early nesting. However, stochastic environmental effects may have precluded response to this apparent selection pressure. Our results suggest that females breeding early in the season have the greatest reproductive value, as these birds lay the largest clutches and have the highest probability of successfully hatching. We developed stochastic, stage-based, matrix population models that incorporated observed spatio-temporal (process) variance and co-variation in vital rates, and projected the stable stage distribution () and population growth rate (λ). We used perturbation analyses to examine the relative influence of changes in vital rates on λ and variance deco

Among numerous anthropogenic impacts on terrestrial landscapes, expanding transportation networks represent one of the primary challenges to wildlife conservation worldwide. Larger mammals may be particularly vulnerable because of typically low densities, low reproductive rates, and extensive movements. Although numerous studies have been conducted to document impacts of road networks on wildlife, inference has been limited because of experimental design limitations. During the last decade, the North Carolina Department of Transportation (NCDOT) rerouted and upgraded sections of United States Highway 64 between Raleigh and the Outer Banks to a 4-lane, divided highway. A new route was selected for a 24.1-km section in Washington County. The new section of highway included 3 wildlife underpasses with adjacent wildlife fencing to mitigate the effects of the highway on wildlife, particularly American black bears (Ursus americanus). We assessed the short-term impacts of the new highway on spatial ecology, population size, survival, occupancy, and gene flow of black bears. We tested our research hypotheses using a before-after control-impact (BACI) study design. We collected data during 2000–2001 (preconstruction phase) and 2006–2007 (postconstruction phase) in the highway project area and a nearby control area (each approx. 11,000 ha), resulting in 4 groups of data (i.e., pre- or postconstruction study phase, treatment or control area). We captured and radiocollared 57 bears and collected 5,775 hourly locations and 4,998 daily locations. Using mixed-model analysis of variance and logistic regression, we detected no differences in home ranges, movement characteristics, proximity to the highway alignment, or habitat use between the 2 study phases, although minimum detectable effect sizes were large for several tests. However, after completion of the new highway, bears on the treatment area became less inactive in morning, when highway traffic was low, compared with bears on the control area (F_{1, 43} = 6.05, P = 0.018). We used DNA from hair samples to determine if population size and site occupancy decreased following highway construction. For each study phase, we collected black bear hair from 70 hair snares on each study area during 7 weekly sampling periods and generated genotypes using 10 microsatellite loci. We used the multilocus genotypes to obtain capture histories for 226 different bears and used capture-mark-recapture models to estimate population size. Model-averaged estimates of population size decreased on the treatment area from 87.7 bears before construction to 31.6 bears after construction (64% reduction) and on the control area from 163.6 bears to 108.2 bears (34% reduction). Permutation procedures indicated this reduction was proportionally greater for the treatment area (P = 0.086). We also applied a spatially explicit capture-recapture technique to test our research hypothesis. The model with

Population fragmentation compromises population viability, reduces a species ability to respond to climate change, and ultimately may reduce biodiversity. We studied the current state and potential causes of fragmentation in grizzly bears over approximately 1,000,000 km² of western Canada, the northern United States (US), and southeast Alaska. We compiled much of our data from projects undertaken with a variety of research objectives including population estimation and trend, landscape fragmentation, habitat selection, vital rates, and response to human development. Our primary analytical techniques stemmed from genetic analysis of 3,134 bears, supplemented with radiotelemetry data from 792 bears. We used 15 locus microsatellite data coupled with measures of genetic distance, isolation-by-distance (IBD) analysis, analysis of covariance (ANCOVA), linear multiple regression, multi-factorial correspondence analysis (to identify population divisions or fractures with no a priori assumption of group membership), and population-assignment methods to detect individual migrants between immediately adjacent areas. These data corroborated observations of inter-area movements from our telemetry database. In northern areas, we found a spatial genetic pattern of IBD, although there was evidence of natural fragmentation from the rugged heavily glaciated coast mountains of British Columbia (BC) and the Yukon. These results contrasted with the spatial pattern of fragmentation in more southern parts of their distribution. Near the Canada–US border area, we found extensive fragmentation that corresponded to settled mountain valleys and major highways. Genetic distances across developed valleys were elevated relative to those across undeveloped valleys in central and northern BC. In disturbed areas, most inter-area movements detected were made by male bears, with few female migrants identified. North–south movements within mountain ranges (Mts) and across BC Highway 3 were more common than east–west movements across settled mountain valleys separating Mts. Our results suggest that relatively distinct subpopulations exist in this region, including the Cabinet, Selkirk South, and the decades-isolated Yellowstone populations. Current movement rates do not appear sufficient to consider the subpopulations we identify along the Canada–US border as 1 inter-breeding unit. Although we detected enough male movement to mediate gene flow, the current low rate of female movement detected among areas is insufficient to provide a demographic rescue effect between areas in the immediate future (0–15 yr). In Alberta, we found fragmentation corresponded to major east–west highways (Highways 3, 11, 16, and 43) and most inter-area movements were made by males. Gene flow and movement rates between Alberta and BC were highest across the Continental Divide south of Highway 1 and north of Highway 16. In the central region between Highways 1 and 11, we found evidence of natur

We assessed the effectiveness of an extensive and unprecedented wildlife reduction effort directed at a wide-ranging migratory population of geese. Population reduction efforts that targeted several populations of light geese (greater snow geese [Chen caerulescens atlantica], lesser snow geese [C. c. caerulescens], and Ross's geese [C. rossii]) began in 1999 in central and eastern North America. Such efforts were motivated by a broad consensus that abundance of these geese was causing serious ecological damage to terrestrial and salt marsh ecosystems in central and eastern parts of the Canadian Arctic and subarctic regions along Hudson Bay. Starting in February 1999, special conservation measures (or, in the U.S., a conservation order) were added to the respective federal regulations that permitted hunters to take snow geese (in parts of Canada and the U.S.) and Ross's geese (in parts of the U.S.) during specified harvest periods outside of the hunting season. These measures were accompanied by increase or removal of daily kill and possession limits and by permissions to use previously prohibited equipment for hunting these species in certain regions of the continent. The intent was to reduce adult survival through increased hunting mortality, which was judged to be the most cost-effective approach to reversing population growth. Our principal goal was to assess the effectiveness of reduction efforts directed at the midcontinent population of lesser snow geese, which was thought to be the most serious threat to arctic and subarctic ecosystems of the 3 light goose populations. Our multiple objectives included the estimation and detection of change in the response measures of total annual harvest, harvest rate, survival rate, and abundance, using the 1998 hunting period (defined as 1 Aug 1998 to 31 Jul 1999) as a point of reference. We used information about hunter recoveries of leg-banded snow geese and estimates of regular-season harvest to estimate 1) conservation-order harvest and total annual harvest, 2) geographic and temporal distribution of recoveries by age class, 3) survival and recovery probability, and 4) abundance of snow geese each August using Lincoln's (1930) method. We also modeled population growth to infer the form of population response to management efforts. Toward that end, we also proposed a method of estimating conservation-order harvest and tested for differences in band-reporting rate between Canada and the United States. Overall, the balance of evidence favored the conclusion that the midcontinent population has continued to grow during the conservation order, although perhaps at a reduced rate. We suggest that annual rate of population growth , derived from estimates of annual population size in August, likely provides the most reliable inference about change in the midcontinent population. There was a decline in annual survival probability between these 2 periods from ab

Manipulating predator populations is often posed as a solution to depressed ungulate populations. However, predator–prey dynamics are complex and the effect on prey populations is often an interaction of predator life history, climate, prey density, and habitat quality. The effect of predator removal on ungulate and, more specifically, mule deer (Odocoileus hemionus) populations has not been adequately investigated at a management scale. We tested the efficacy of removing coyotes (Canis latrans) and mountain lions (Puma concolor) for increasing survival and population growth rate of mule deer in southeastern Idaho, USA, during 1997–2003. We assigned 8 game management units (GMUs) to treatments under a 2 × 2 factorial design (treatments of coyote removal and lion removal) with 2 replicates of each treatment or reference area combination. We used methods typically available to wildlife managers to achieve predator removals and a combination of extensive and intensive monitoring in these 8 GMUs to test the hypothesis that predator removal increased vital rates and population growth rate of mule deer. We determined effects of predator removal on survival and causes of mortality in 2 intensive study sites, one with coyote and mountain lion removal and one without. We also considered the effects of other variables on survival including lagomorph abundance and climatic conditions. In these 2 intensive study areas, we monitored with radiotelemetry 250 neonates, 284 6-month-old fawns, and 521 adult females. At the extensive scale, we monitored mule deer population trend and December fawn ratios with helicopter surveys. Coyote removal decreased neonate mortality only when deer were apparently needed as alternate prey, thus removal was more effective when lagomorph populations were reduced. The best mortality model of mule deer captured at 6 months of age included summer precipitation, winter precipitation, fawn mass, and mountain lion removal. Over-winter mortality of adult female mule deer decreased with removal of mountain lions. Precipitation variables were included in most competing mortality models for all age classes of mule deer. Mountain lion removal increased fawn ratios and our models predicted fawn ratios would increase 6% at average removal rates (3.53/1,000 km²) and 27% at maximum removal rates (14.18/1,000 km²). Across our extensive set of 8 GMUs, coyote removal had no effect on December fawn ratios. We also detected no strong effect of coyote or mountain lion removal alone on mule deer population trend; the best population-growth-rate model included previous year's mountain lion removal and winter severity, yet explained only 27% of the variance in population growth rate. Winter severity in the current and previous winter was the most important influence on mule deer population growth. The lack of response in fawn ratio or mule deer abundance to coyote reduction at this extensive (landscape) scal

Military lands are a valuable resource in recovery of threatened, endangered, and at-risk species worldwide and have the highest density of threatened and endangered species of all major land management agencies in the United States. Many red-cockaded woodpeckers (Picoides borealis) that reside on federal lands occur on 15 military installations in the southeastern United States. This close association has increased concern over potential conflicts between conservation requirements of endangered species and the military's mission of combat readiness. Our objectives were to 1) determine if military training operations affect behavior, reproductive success, and productivity of red-cockaded woodpeckers; 2) develop a frequency-weighting function to assess woodpecker hearing sensitivity; 3) identify factors that affect woodpecker responses to military training operations; 4) develop distance and dose-response thresholds for quantifying woodpecker responses to noise levels and stimulus distances; 5) characterize military training operations through quantification of sound levels, source identification, distance from active woodpecker nests, frequency spectra, duration, and frequency of occurrence; and 6) document baseline woodpecker nesting behavior. We conducted our study on the Fort Stewart Military Installation located in southeast Georgia, USA.

Downy woodpeckers, as surrogates for red-cockaded woodpeckers, had their best hearing sensitivity within the peak range of the power spectrum of both downy and red-cockaded woodpecker vocalizations, which is at a higher frequency than that of a typical passerine. Overall, woodpeckers had a reduced auditory sensitivity relative to human hearing sensitivity and other species of small birds, especially in the frequency range >4 kHz. Woodpeckers were most sensitive in the 1.5- to 4.0-kHz range. Sensitivity appeared to drop off quickly at frequencies <1.0 kHz and >4.0 kHz. Overall, we did not find that the woodpecker-frequency-weighting function we developed provided a better predictor of woodpecker flush response compared with A-weighting. More research is needed to better understand the relationship between frequency-weighting functions and woodpecker response behavior.

Potential breeding groups of woodpeckers across the population increased from 158 in 1997 to 181 in 2000, wheras nesting groups increased from 141 in 1998 to 170 in 2000, for overall increases of 14.6% and 20.6%, respectively, over the 3 years of this project. Fledging success rates for individual nests within the overall population remained consistent from 1998 to 2000, averaging 84.4%. Mean clutch sizes for woodpecker groups for 1998 to 2000 ranged from 2.75 to 3.01 eggs/nest, brood size ranged from 2.01 to 2.22 nestlings/nest, whereas the average number of young fledged ranged from 1.57 to 1.76 young/occupied nest. We observed no difference in reproductive success or productivity between experimental and control

Invasions by nonnative plants have changed the structure of many terrestrial ecosystems and altered important ecological processes such as fire, the dominant driver in grassland ecosystems. Reestablishing fire has been proposed as a mechanism to restore dominance of native plants in grasslands invaded by nonnative plants, yet fire may function differently in these altered systems, potentially affecting animals in novel ways. To assess whether invasions by nonnative plants alter the effects of fire on animals, we performed a manipulative experiment in semi-desert grasslands of southeastern Arizona that have been invaded by a perennial, nonnative grass from Africa, Lehmann lovegrass (Eragrostis lehmanniana). We applied fire to 36 of 54 1-ha plots established along an invasion gradient where dominance of E. lehmanniana ranged from 0% to 91% of total live plant biomass. Over the 5-year period from 2000 to 2004, we used mark-recapture methods to assess how population and community attributes of small mammals varied along the gradient of nonnative grass and in response to fire. We quantified changes in presence of 17 species, abundance of 9 species, total abundance of all species combined, species richness, and species composition. Based on 11,226 individual mammals from 24 species, we found that effects of nonnative-grass dominance varied with habitat preferences of each species, resulting in composition of the small-mammal community changing predictably along the invasion gradient. As dominance of nonnative grass increased, presence and abundance of granivorous heteromyids and insectivores (e.g., Chaetodipus, Perognathus, Onychomys; pocket mice and grasshopper mice) decreased, whereas presence and abundance of omnivorous and herbivorous murids (e.g., Reithrodontomys, Sigmodon; harvest mice and cotton rats) increased. Species richness of the small-mammal community averaged 8.4 species per plot and was highest at intermediate levels of nonnative-grass dominance where vegetation heterogeneity was greatest. Abundance of all small mammals combined averaged 26.9 individuals per plot and did not vary appreciably with nonnative-grass dominance. During the 4- to 8-week period immediately after fire, abundance of 6 of the 9 most common species changed, with 5 species decreasing and 1 species increasing on burned plots relative to unburned plots. During this same time period, species richness of small mammals decreased by an average of 3 species (38%) and total abundance of all species combined decreased by an average of 16 individuals (61%) on burned plots relative to unburned plots. Effects of fire on vegetation biomass, on presence of 9 of 17 mammalian species, and on abundance of 4 of 9 mammalian species remained evident ≥2 years after fire. Effects of fire on most small-mammal species varied with the degree of nonnative-grass dominance, suggesting that fire functioned differently in areas invaded by nonna

The Mid-continent Population (MCP) of sandhill cranes (Grus canadensis) is widely hunted in North America and is separated into the Gulf Coast Subpopulation and Western Subpopulation for management purposes. Effective harvest management of the MCP requires detailed knowledge of breeding distribution of subspecies and subpopulations, chronology of their use of fall staging areas and wintering grounds, and exposure to and harvest from hunting. To address these information needs, we tagged 153 sandhill cranes with Platform Transmitting Terminals (PTTs) during 22 February–12 April 1998–2003 in the Central and North Platte River valleys of south-central Nebraska. We monitored PTT-tagged sandhill cranes, hereafter tagged cranes, from their arrival to departure from breeding grounds, during their fall migration, and throughout winter using the Argos satellite tracking system. The tracking effort yielded 74,041 useable locations over 49,350 tag days; median duration of tracking of individual cranes was 352 days and 73 cranes were tracked >12 months. Genetic sequencing of mitochondrial DNA (mtDNA) from blood samples taken from each of our random sample of tagged cranes indicated 64% were G. c. canadensis and 34% were Grus canadensis tabida. Tagged cranes during the breeding season settled in northern temperate, subarctic, and arctic North America (U.S. [23%, n = 35], Canada [57%, n = 87]) and arctic regions of northeast Asia (Russia [20%, n = 31]). Distribution of tagged cranes by breeding affiliation was as follows: Western Alaska–Siberia (WA–S, 42 ± 4% [SE]), northern Canada–Nunavut (NC–N, 21 ± 4%), west-central Canada–Alaska (WC–A, 23 ± 4%) and East-central Canada–Minnesota (EC–M, 14 ± 3%). All tagged cranes returned to the same breeding affiliation used during the previous year with a median distance of 1.60 km (range: 0.08–7.7 km, n = 53) separating sites used in year 1 and year 2. Fall staging occurred primarily in central and western Saskatchewan (69%), North Dakota (16%), southwestern Manitoba (10%), and northwestern Minnesota (3%). Space-use sharing indices showed that except for NC–N and WC–A birds, probability of finding a crane from one breeding affiliation within the home range of another breeding affiliation was low during fall staging. Tagged cranes from WC–A and EC–M breeding affiliations, on average, spent 25 and 20 days, respectively, longer on fall staging areas in the northern plains than did WA–S and NC–N birds. Cranes in the NC–N, WA–S, and WC–A affiliations spent 99%, 74%, and 64%, respectively, of winter in western Texas in Hunting Zone A; EC–M cranes spent 83% of winter along the Texas Gulf Coast in Hunting Zone C. Tagged cranes that settled within the breeding range of the Gulf Coast Subpopulation spent 28% and 42% of fall staging and winter within the range of the Western Subpopulation, indicating sufficient exchange of birds to potentially limit effectiveness of MCP harvest