Showing papers in "Journal of Wildlife Management in 2004"

Use and interpretation of logistic regression in habitat-selection studies

Abstract: Logistic regression is an important tool for wildlife habitat-selection studies, but the method frequently has been misapplied due to an inadequate understanding of the logistic model, its interpretation, and the influence of sampling design. To promote better use of this method, we review its application and interpretation under 3 sampling designs: random, case–control, and use–availability. Logistic regression is appropriate for habitat use–nonuse studies employing random sampling and can be used to directly model the conditional probability of use in such cases. Logistic regression also is appropriate for studies employing case–control sampling designs, but careful attention is required to interpret results correctly. Unless bias can be estimated or probability of use is small for all habitats, results of case–control studies should be interpreted as odds ratios, rather than probability of use or relative probability of use. When data are gathered under a use–availability design, logistic regr...

Efficacy of hunting, feeding, and fencing to reduce crop damage by wild boars

Abstract: Since 1980, populations of wild boar (Sus scrofa) have increased over the species' entire European range. This increase has led to conflicts because wild boars cause crop damage amounting to several million U.S. dollars every year. Wildlife management agencies promote and financially support 3 major methods to reduce the loss: (1) intensive harvest, (2) supplemental feeding in forests to bait animals for easier shooting and to distract them from agricultural fields, and (3) building electrical fences around crops at risk. Our objective was to investigate how effective these methods were in reducing field damage by wild boars. Based on data from 44 hunting territories in the Canton Thurgau, Switzerland, we related damage frequency to harvest success, supplemental feeding, and fencing effort by means of 2 multiple regression analyses. The analysis of mean damage frequency among territories (averaged over 3 years) and changes in damage frequency within territories from 1994 to 1996 showed that only hunting reduced damage by wild boars. Because our results question the effectiveness of wild boar management practices and wild boar populations and damage are increasing throughout Europe, we suggest that control efforts and funds be reconsidered. Because only hunting seems to clearly reduce wild boar damage, we suggest more emphasis be put on the development and introduction of new harvest models among local hunting teams.

Estimating grizzly bear distribution and abundance relative to habitat and human influence

Abstract: Understanding factors that influence and predict grizzly bear (Ursus arctos) distribution and abundance is fundamental to their conservation. In southeast British Columbia, Canada, we applied DNA hair-trap sampling (1) to evaluate relationships of grizzly bear detections with landscape variables of habitat and human activity, and (2) to model the spatial distribution and abundance of grizzly bears. During 1996–1998, we sampled grizzly bear occurrence across 5,496 km2 at sites distributed according to grid cells. We compared 244 combinations of sampling sites and sessions where grizzly bears were detected (determined by nDNA analyses) to 845 site–sessions where they were not. We tested for differences in 30 terrain, vegetation, land cover, and human influence variables at 3 spatial scales. Grizzly bears more often were detected in landscapes of relatively high elevation, steep slope, rugged terrain, and low human access and linear disturbance densities. These landscapes also were comprised of more...

Winter prey selection and estimation of wolf kill rates in yellowstone national park, 1995–2000

Abstract: Wolf (Canis lupus) impacts on prey are a central post-wolf-reintroduction issue in the greater Yellowstone ecosystem (GYE) of the western United States. Further, estimates of wolf kill rates, used to understand these impacts, can be biased due to unrecovered kills. In Yellowstone National Park (YNP), visibility of wolves allowed us to combine independent aerial and ground observations and use a double-count method to estimate the probability of recovering kills. We consequently used these data to adjust estimates of wolf kill rates. We conducted monitoring annually from 1995 to 2000 during 2 30-day periods in early (15 Nov–14 Dec) and late winter (Mar). Estimated recovery rates of wolf kills for ground and aerial crews were 50% and 45%, respectively, although we determined that this varied by location (distance from road) and possibly age (calf or adult) of the kill. The estimated combined recovery rate was 73%. Estimated wolf kill rates were higher in late winter (2.2 kills/wolf/month) compared ...

Spatial separation of caribou from moose and its relation to predation by wolves

Abstract: In northeastern Alberta, Canada, continued expansion of the oil and gas industry along with timber harvesting has raised concerns that the resulting environmental changes may negatively affect the woodland caribou (Rangifer tarandus caribou) population in this region. Caribou are a threatened species in Alberta, and populations in northeastern Alberta appear to be stable or slightly decreasing. The spatial distribution of caribou in relation to alternative prey (commonly moose [Alces alces]) has been hypothesized to affect the level of wolf (Canis lupus) predation on caribou populations. We monitored radiomarked caribou, moose, and wolves between 1993 and 1997, and we found that selection of fen/bog complexes by caribou and selection of well-drained habitats by moose and wolves resulted in spatial separation. This spatial separation in turn reduced wolf predation pressure on caribou but did not provide a total refuge from wolves. Any management activities that increase the density of moose and wo...

Genetic errors associated with population estimation using non‐invasive molecular tagging: problems and new solutions

Abstract: The use of non-invasive DNA-based sampling is becoming increasingly popular. However, the misidentification of individuals due to genotyping error (primarily allelic dropout) is a critical problem, especially when using individuals in the capture–mark–recapture (CMR) approach to estimate population size. We propose 2 simple and cost-effective tests, Examining Bimodality (EB) and Difference in Capture History (DCH), to determine whether a sample contains genotyping errors and the relative magnitude of the problem. These tests formalize currently used approaches for identifying genotyping errors. We evaluate the efficacy of these tests using simulated CMR data. Results show that both tests are effective at detecting genotyping errors and provide a strong indication of whether the data are error free. The EB and DCH tests apply to data in which multiple samples are associated with individuals, such as those generated by CMR sampling. Managers need to be able to identify and eliminate genotyping erro...

Estimating detection probability parameters for plethodon salamanders using the robust capture–recapture design

Abstract: Recent concern over global amphibian population declines has highlighted a need for more extensive, rigorous monitoring programs. Two sources of variation, spatial variation and variation in detection probability, make the design and implementation of effective monitoring programs difficult. We used Pollock's robust design in a 3-year capture–recapture study to estimate detection probability and temporary emigration for Plethodon salamanders in Great Smoky Mountains National Park (Tennessee/North Carolina), USA. We used 12 competing models to determine the importance of temporary emigration, and we explored temporal and behavioral effects on conditional capture probabilities. The top 4 models all included random temporary emigration, and Akaike model weights indicated that this parameter was the most important. Models that contained behavioral effects in capture probabilities were selected more often than models with equal capture probabilities for marked and previously unmarked individuals. The ...

High potential for competition between guanacos and sheep in patagonia

Abstract: Guanacos (Lama guanicoe) are the largest native Artiodactyl in South America and the most widely distributed. In arid Patagonia, densities are low and negatively related to domestic sheep numbers in space and time consistent with interspecific competition theory. Although guanacos and domestic sheep have been described as intermediate feeders sharing food resources, no studies have been conducted to compare their diets in sympatric conditions and explore whether the potential exists for direct interspecific competition. We assessed the diet of both species across 9 different sites and 2 seasons by microhistological analysis of fecal samples. We found that (1) guanacos and sheep are generalist herbivores feeding on a wide range of plant species; (2) both are intermediate feeders able to include both monocotyledoneous and dicotyledoneous plants in their diet; (3) both are able to change their diets seasonally; and (4) food niche overlap is high, particularly in summer when food resources are more scarce than in spring. We conclude that the potential for competition between guanacos and sheep is high and could have played a major role in the demise of guanacos. Consequently, current management practices focused on maximizing sheep numbers are not compatible with the recovery of guanaco populations.

Spatial ecology of coyotes along a suburban-to-rural gradient

Abstract: Coyotes (Canis latrans) are now ubiquitous throughout most of the eastern United States; however, little information exists on how they are able to exploit and thrive in fragmented landscapes. We investigated home ranges, movements, and scale-dependent resource selection of coyotes along a gradient (suburban/exurban/rural) of anthropogenic disturbance. Home-range sizes varied along a suburban-to-rural gradient and were inversely correlated to urbanization (R2 = 0.79, P < 0.001). Habitat composition and coyote use of 95% (home range) and 50% (core area) contours were nonrandom. Coyotes used corridor habitat extensively and avoided urban and crop-field habitats. Forested habitat was used extensively for diurnal cover. Rural coyotes traveled greater distances at faster rates than did suburban/exurban coyotes. Diel activity patterns were similar along the gradient, suggesting that coyotes responded similarly to differing levels and types of human activity. Coyotes appeared to assess habitat quality a...

Habitat selection by mule deer: forage benefits or risk of predation?

Abstract: Risk of predation may affect individuals in prey populations by limiting their use of high-quality habitat. Predation risk, however, cannot be implicated as a factor in habitat selection by prey without data comparing quality of selected and avoided habitats, along with the predation risk associated with those habitats. If forage benefits and predation risk are not positively correlated among habitat types, then predation risk may have little influence on the habitat selected by prey. We evaluated habitat selection by mountain lions (Puma concolor) and mule deer (Odocoileus hemionus) in the eastern Sierra Nevada, California, USA, from 1994 to 1997, to determine how forage benefit or risk of predation by mountain lions affects habitat selection by mule deer. Mountain lions were the primary predator of mule deer in our study area. Stands of bitterbrush (Purshia tridentata) in the Great Basin provided more cover for mule deer than surrounding patches of rabbitbrush (Chrysothamnus nauseosum) or deser...

Comparison of type i error rates for statistical analyses of resource selection

Abstract: During the past decade, compositional analysis (CA) has been used widely in wildlife habitat and resource selection studies. However, critical aspects of CA have not been tested for potential systematic biases such as an inflated Type I error rate. We used computer-simulated data based on known habitat use and availability parameters and found that compositional analysis could result in large Type I error rates. These inflated Type I errors occurred when available habitat types that were not used by animals were included in the resource selection analysis. These error rates arise because of the recommended substitution of an arbitrarily small value, such as 0.01, for each 0% utilization value for any animal. We observed, based on a series of computer-simulation analyses, that progressively larger Type I error rates in CA resulted from substituting progressively smaller positive values for each 0% utilization of a habitat category. The Type I error rate in CA also increased when the number of experimental animals was increased for a fixed number of observations per animal. Two other resource selection analysis methods (Neu et al. [1974] and the Euclidean distance-based analysis [DA] method of Conner and Plowman [2001]) did not exhibit inflated Type I error rates for the same simulated data. Our computer simulations cause us to question the veracity of CA habitat selection analyses that include habitat patches or categories with relatively small areas of availabilities and 0% use.

Sampling design and bias in dna-based capture-mark- recapture population and density estimates of grizzly bears

Abstract: Over a 3-year period, we assessed 2 sampling designs for estimating grizzly bear (Ursus arctos) population size using DNA capture–mark–recapture methods on a population of bears that included radiomarked individuals. We compared a large-scale design (with 8 × 8-km grid cells and sites moved for 4 sessions) and a small-scale design (5 × 5-km grid cells with sites not moved for 5 sessions) for closure violation, capture-probability variation, and estimate precision. We used joint telemetry/capture–mark–recapture (JTMR) analysis and traditional closure tests to analyze the capture–mark–recapture data with each design. A simulation study compared the performance of each design for robustness to heterogeneity bias caused by reduced capture probabilities of cubs. Our results suggested that the 5 × 5-km grid cell design was more precise and more robust to potential sample biases, but the risk of closure violation due to smaller overall grid size was greater. No design exhibited complete closure as estim...

Spatial and temporal variation in detection probability of plethodon salamanders using the robust capture‐recapture design

Abstract: Recent worldwide amphibian declines have highlighted a need for long-term, large-scale monitoring programs. Scientific or management objectives, appropriate spatial sampling, and detectability all must be considered when designing monitoring programs (Yoccoz et al. 2001). The ability to establish meaningful monitoring programs currently is compromised by a lack of information about amphibian detection probabilities. We used Pollock's robust design and capture–recapture models that included temporary emigration to test a priori hypotheses about spatial and temporal variation in salamander detection probability parameters for populations found in Great Smoky Mountains National Park (Tennessee/North Carolina), USA. We explored the effects of 3 large-scale habitat characteristics (disturbance history, elevation, vegetation type) and found that vegetation type and elevation were correlated with detection probabilities. Vegetation type was an important covariant in estimates of temporary emigration, co...

Assessing seabird mortality from chronic oil discharges at sea

Abstract: Chronic marine oil pollution is an ongoing global problem, yet no model currently exists to assess seabird mortality from continuous low-level inputs of oil. Taking into account persistence and detection rates of birds on beaches, and the wind-dependent proportion of birds lost at sea, we present a general mathematical Oiled Seabird Mortality Model (OSMM) to assess seabird mortality due to chronic oil pollution along a given coastline, using birds counted during systematic beached-bird surveys. We applied our OSMM to Newfoundland, Canada, where the incidence of chronic oil pollution is among the highest in world. We estimated that between 1998 and 2000, an average of 315,000 ± 65,000 murres (common [Uria aalge] and thick-billed [U. lomvia]) and dovekies (Alle alle) were killed annually in southeastern Newfoundland due to illegal discharges of oil from ships. Thick-billed murres that overwinter on the Grand Banks made up 67% of this kill. This species already is subject to extensive summer and win...

Interspecific and intersexual variation in roost‐site selection of northern long‐eared and little brown bats in the greater fundy national park ecosystem

Abstract: Although only 2 bat species are common in the Greater Fundy National Park Ecosystem of New Brunswick, Canada, 4 distinct groups occur in terms of roost-site selection due to sexual segregation. We found that female northern long-eared bats (Myotis septentrionalis) roosted alone or as part of maternity colonies in mature, shade-tolerant deciduous stands. A roost site was 24 times more likely to be in a shade-tolerant deciduous tree than a coniferous tree, and trees in the mid-decay classes were 5.2 times more likely to be used than live or recently dead trees. Male northern long-eared bats roosted alone in coniferous stands or conifer-dominated mixedwood stands, and they selected roost trees that were in the mid-decay stages. Trees in mid-decay stages were selected more than twice as often as trees at the early or late stages of decay. For every 10% increase in the proportion of coniferous trees in the plot, the chances of a male northern long-eared bat roosting in the plot increased 1.5 times. Fe...

Resting habitat selection by fishers in California

Abstract: We studied the resting habitat ecology of fishers (Martes pennanti) in 2 disjunct populations in California, USA: the northwestern coastal mountains (hereafter, Coastal) and the southern Sierra Nevada (hereafter, Sierra). We described resting structures and compared features surrounding resting structures (the resting site) with those at randomly selected sites that also were centered on a large structure. We developed Resource Selection Functions (RSFs) using logistic regression to model selection of resting sites within home ranges, and we evaluated alternative models using an information–theoretic approach. Forty-five fishers were radiomarked, resulting in 599 resting locations. Standing trees (live and dead) were the most common resting structures, with California black oak (Quercus kelloggii) and Douglas-fir (Psuedotsuga menziesii) the most frequent species in the Sierra and Coastal study areas, respectively. Resting structures were among the largest diameter trees available, averaging 117.3 ± 45.2 (mean ± SE) cm for live conifers, 119.8 ± 45.3 for conifer snags, and 69.0 ± 24.7 for hardwoods. Females used cavity structures more often than males, while males used platform structures significantly more than females. The diversity of types and sizes of rest structures used by males suggested that males were less selective than females. In the Sierra study area, where surface water was less common, we found almost twice as many resting sites as random points within 100 m of water. Multivariate regression analysis resulted in the selection of RSFs for 4 subsets of the data: all individuals, Sierra only, Coastal only, and females only. The top model for the combined analysis indicated that fishers in California select sites for resting with a combination of dense canopies, large maximum tree sizes, and steep slopes. In the Sierra study area, the presence of nearby water and the contribution of hardwoods were more important model parameters than in the Coastal area, where the presence of large conifer snags was an important predictor. Based on our results, managers can maintain resting habitat for fishers by favoring the retention of large trees and the recruitment of trees that achieve the largest sizes. Maintaining dense canopy in the vicinity of large trees, especially if structural diversity is increased, will improve the attractiveness of these large trees to fishers.

Vigilance, predation risk, and the allee effect in desert bighorn sheep

Abstract: Knowledge of how predation risk affects population survivorship is important for understanding predator–prey relationships and designing effective conservation strategies. The Allee effect (inverse density dependence) can be generated when antipredator strategies become inefficient in small groups of prey, thus making the population more susceptible to catastrophic population collapse and extinction. Many populations of desert bighorn sheep (Ovis canadensis) are declining, and predation is, in many cases, a major mortality factor. We studied desert bighorns at the Red Rock Wildlife Area, New Mexico, USA, to assess predation risk in different group types (ram, ewe, mixed) and age–sex classes. Multiple regression analysis revealed that predation risk (as estimated by individual vigilance) increased with smaller group size and greater inter-individual distance for all bighorns, with groups of <5 individuals subject to the greatest risk. Although rugged terrain is thought to provide refuge from preda...

Relationship between changes in beechnut production and asiatic black bears in northern japan

Abstract: Minimizing human-caused mortality by providing alternative solutions to human–bear conflicts is important for the conservation and management of Asiatic black bear (Ursus thibetanus) populations. We found a positive correlation (P < 0.05) between the number of nuisance bears killed and a beechnut (Fagus crenata) crop failure index in 5 of 7 zones in the Tohoku region of Japan. In areas where bears are highly dependent on beechnuts as food in autumn, we suggest that agencies could issue warnings about nuisance bears in years of crop failure using the current monitoring network of beechnut production. This system could be a valuable method not only to reduce human–bear conflicts but also to enhance public consciousness of bear conservation and management.

The influence of mountain lion predation on bighorn sheep translocations

Abstract: We studied the effects of mountain lion (Puma concolor) predation on 2 translocated populations of bighorn sheep (Ovis canadensis) in New Mexico, USA. During 1993, 32 Rocky Mountain bighorn sheep (O. c. canadensis) were translocated to Wheeler Peak Wilderness Area in northern New Mexico, and during 1992–1993, 31 desert bighorn sheep (O. c. mexicana) were translocated to Sierra Ladron in central New Mexico. We monitored both populations from release through 2000 using fixed-wing aircraft and ground and/or helicopter surveys. We determined cause of mortality for radiomarked individuals (n = 26) and calculated survival rates, cause-specific mortality rates, exponential growth rates, and lamb:ewe ratios. The post-lambing population estimates in 2000 were 180 in Wheeler Peak and 21 in Sierra Ladron. Annual adult survival was higher (P < 0.005) in the Wheeler Peak population (0.955) than in the Sierra Ladron population (0.784). Annual lamb:ewe ratios also were higher (P < 0.001) in the Wheeler Peak pop...

Effects of infrastructure on migration and range use of wild reindeer

Abstract: We studied reindeer (Rangifer tarandus tarandus) distribution in relation to possible travel barriers (roads and power lines) in south-central Norway, 1997–2000, using lichen biomass as an indicator of reindeer use. We recorded lichen cover on both sides of potential barriers within comparable habitat in 42 sites for 3 different reindeer herds. We used cover–biomass regressions to assess the relationship between lichen cover and biomass. In 2 of the regions, lichen biomass was 5.3 times and 2.8 times higher in areas isolated by 2 parallel power lines and an adjacent winter-closed road compared to biomass on the other side of the potential barrier. In a third region, lichen biomass did not vary significantly between areas on either side of a single winter-closed road. Lichen biomass data suggested that wild reindeer used both sides of a closed road in winter, whereas 2 parallel power lines and a winter-closed road in combination reduced reindeer migration and resulted in very different grazing pre...

Do individual differences influence flight initiation distance

Abstract: Flight initiation distance (FID), or the distance between a prey animal and an approaching intruder when the prey initiates its escape, is an important factor in wildlife management. We conducted a study on individually identified yellow-bellied marmots (Marmota flaviventris) to test 3 key assumptions of FID research: (1) differences in individual responses are small enough so as not to confound results; (2) pseudoreplication may bias results; and (3) habituation and sensitization can be studied without knowledge of individuals. We found that individual identity was not a significant predictor of FID. Furthermore, a moderate degree of pseudoreplication did not significantly affect the results of most analyses. However, individuals differed greatly in their rates of habituation, such that habituation was apparent only when individual identity was known and could not be detected without knowledge of individuals. If our marmot results can be generalized to other species, they suggest that researchers need not be concerned about individual identity when studying variables largely dependent on environmental factors, but that identification of individuals is important for studies of properties of individuals, such as habituation.

Modeling demographic performance of northern spotted owls relative to forest habitat in oregon

Abstract: Northern spotted owls (Strix occidentalis caurina) are known to be associated with late-successional forests in the Pacific Northwest of the United States, but the effects of habitat on their demographic performance are relatively unknown. We developed statistical models relating owl survival and productivity to forest cover types within the Roseburg Study Area in the Oregon Coast Range of Oregon, USA. We further combined these demographic parameters using a Leslie-type matrix to obtain an estimate of habitat fitness potential for each owl territory (n = 94). We used mark–recapture methods to develop models for survival and linear mixed models for productivity. We measured forest composition and landscape patterns at 3 landscape scales centered on nest and activity sites within owl territories using an aerial photo-based map and a Geographic Information System (GIS). We also considered additional covariates such as age, sex, and presence of barred owls (Strix varia), and seasonal climate variable...

Integrating wildlife and human-dimensions research methods to study hunters

Abstract: Recreational hunting is the primary management tool used by natural resource agencies to control ungulate populations. Although free-ranging ungulates have been studied extensively in North America, relatively little is known about the field behavior of hunters or the factors that influence hunting behavior, except on small study areas where access is limited and controlled. We developed 3 integrated protocols to estimate hunter density, distribution, movements, habitat use, characteristics, and attitudes, which can be used on large areas with unrestricted access. We described how aerial surveys, in conjunction with distance sampling techniques and a Geographic Information System (GIS) database of landscape characteristics, provide estimates of hunter density and a map of hunter distribution and habitat use. We used Global Positioning System (GPS) units issued to hunters to systematically record hunter locations. Hunters also completed a simple questionnaire. We linked these data and used them to...

Efficacy of black bear supplemental feeding to reduce conifer damage in western washington

Abstract: While searching for food, 1 black bear (Ursus americanus) may girdle 60–70 coniferous trees in a day during the spring months in western Washington, USA. Tree-bark peeling and subsequent foraging on sapwood can result in substantial economic losses for forest landowners. The supplemental feeding program, a nonlethal approach to minimize black bear damage by providing an alternative food source, was developed by the Washington Forest Protection Association (WFPA) in 1986. From 1998 to 2002, I studied the efficacy of this supplemental feeding program on the Olympic Peninsula. I selected 14 conifer stands of approximately 20 ha each for study. Mean pretreatment conifer damage on these sites in 1998 was 26% of trees. In March 1999, 1,000 trees were marked on 4 transects throughout each stand. Two feeding stations were installed on each of 7 randomly chosen stands in April of 1999, while no supplemental feed was supplied on the remaining 7 control stands. I found that bears damaged significantly more ...

Synthesis of survival rates and causes of mortality in north american wolverines

Abstract: Understanding population vital rates is fundamental to the evaluation of conservation options for wolverines (Gulo gulo). We estimated survival rates and causes of wolverine mortality in trapped and untrapped populations within montane, boreal, and tundra environments using data from 12 North American radiotelemetry studies conducted between 1972 and 2001. Rates were based on data for 62 mortalities of 239 radiomarked wolverines. Mortalities included 22 wolverines that were trapped or hunted, 3 road or rail killed, 11 that were predated, 18 that starved, and 8 deaths of unknown cause. Annual survivorship rates were estimated for sex and age class using Kaplan-Meier staggered-entry techniques. Survival was substantially lower in trapped ( 0.84 for all age–sex classes) populations. Human-caused mortality was mostly additive to natural mortality for wolverines in a management context. Logistic growth rate estimates indicated that trapped populations ...

A multi-resolution assessment of raccoon den selection

Abstract: Many studies have been conducted on the ecology of raccoons (Procyon lotor), while few have examined raccoon den-site selection, particularly in agricultural and prairie landscapes. Furthermore, no studies have examined selection of den sites at multiple spatial scales. We examined den-site selection for 48 raccoons during 1997–1999 in an agricultural landscape in the Black Prairie physiographic region of east-central Mississippi, USA. Den types selected by raccoons differed by gender and season. Females used more cavity dens during young rearing, whereas males selected ground dens and brush piles. We found that den sites were located closer to crop fields, roads, and macrohabitat edges than random points. At the landscape level, den sites were associated positively with woody patch size, amounts of woody and grass edge, number of available patches of crop fields, and available area of lakes and ponds. Composition of habitats around den sites differed from composition of habitats within home rang...

Modeling survival: application of the andersen—gill model to yellowstone grizzly bears

Abstract: Wildlife ecologists often use the Kaplan-Meier procedure or Cox proportional hazards model to estimate survival rates, distributions, and magnitude of risk factors. The Andersen–Gill formulation (A–G) of the Cox proportional hazards model has seen limited application to mark–resight data but has a number of advantages, including the ability to accommodate left-censored data, time-varying covariates, multiple events, and discontinuous intervals of risks. We introduce the A–G model including structure of data, interpretation of results, and assessment of assumptions. We then apply the model to 22 years of radiotelemetry data for grizzly bears (Ursus arctos) of the Greater Yellowstone Grizzly Bear Recovery Zone in Montana, Idaho, and Wyoming, USA. We used Akaike's Information Criterion (AICc) and multi-model inference to assess a number of potentially useful predictive models relative to explanatory covariates for demography, human disturbance, and habitat. Using the most parsimonious models, we gen...

Goals and strategies for estimating trends in landbird abundance

Abstract: Reliable estimates of trends in population size are critical to effective management of landbirds. We propose a standard for considering that landbird populations are adequately monitored: 80% power to detect a 50% decline occurring within 20 years, using a 2-tailed test and a significance level of 0.10, and incorporating effects of potential bias. Our standard also requires that at least two-thirds of the target region be covered by the monitoring program. We recommend that the standard be achieved for species' entire ranges or for any area one-third the size of the temperate portions of Canada and the United States, whichever is smaller. We applied our approach to North American Breeding Bird Survey (BBS) data. At present, potential annual bias for the BBS is estimated at ±0.008. Further, the BBS achieves the monitoring standard for only about 42% of landbirds for which the BBS is considered the most effective monitoring approach. Achieving the proposed monitoring target for ≥80% of these speci...