We introduce a Special Section of The Journal of Wildlife Management (JWM) that contains 9 papers describing in theory and in practice a wide range of applications of resource selection statistics, several of which have not been previously published. There is an intense interest in and widespread use of resource selection statistics in the study of wildlife and habitat relationships. There is also debate over the proper application of these methods. We briefly describe the debate and the papers contained in the Special Section. We point out that resource selection statistics, when properly applied, can be a powerful tool in wildlife research.

We review 87 articles published in the Journal of Wildlife Management from 2000 to 2004 to assess the current state of practice in the design and analysis of resource selection studies. Articles were classified into 4 study designs. In design 1, data are collected at the population level because individual animals are not identified. Individual animal selection may be assessed in designs 2 and 3. In design 2, use by each animal is recorded, but availability (or nonuse) is measured only at the population level. Use and availability (or unused) are measured for each animal in design 3. In design 4, resource use is measured multiple times for each animal, and availability (or nonuse) is measured for each use location. Thus, use and availability measures are paired for each use in design 4. The 4 study designs were used about equally in the articles reviewed. The most commonly used statistical analyses were logistic regression (40%) and compositional analysis (25%). We illustrate 4 problem areas in resource selection analyses: pooling of relocation data across animals with differing numbers of relocations, analyzing paired data as though they were independent, tests that do not control experiment wise error rates, and modeling observations as if they were independent when temporal or spatial correlations occurs in the data. Statistical models that allow for variation in individual animal selection rather than pooling are recommended to improve error estimation in population-level selection. Some researchers did not select appropriate statistical analyses for paired data, or their analyses were not well described. Researchers using one-resource-at-a-time procedures often did not control the experiment wise error rate, so simultaneous inference procedures and multivariate assessments of selection are suggested. The time interval between animal relocations was often relatively short, but existing analyses for temporally or spatially correlated data were not used. For studies that used logistic regression, we identified the data type employed: single sample, case control (used–unused), use–availability, or paired use–availability. It was not always clear whether studies intended to compare use to nonuse or use to availability. Despite the popularity of compositional analysis, we do not recommend it for multiple relocation data when use of one or more resources is low. We illustrate that resource selection models are part of a broader collection of statistical models called weighted distributions and recommend some promising areas for future development.

Design and analysis of resource selection studies, where resources, such as habitats, are categorical have been commonly used for the past four decades. These methods have been evaluated, criticized, modified, and extended in the wildlife and statistical science literature. In this paper, we review some of the history of resource selection studies and place these studies in the context of wildlife science. Several variations of resource studies are presented along with historical data sets to illustrate the type of data obtained from some study designs. Common methods of analysis are introduced and compared in the terms of appropriate application to data from the various study designs, underlying assumptions, and hypotheses being tested. Criticisms of several of the methods of analysis are reviewed along with fundamental concerns about resource selection studies from the recent literature. Implications for analysis and interpretation of results are presented along with suggestions for future development. Resource selection studies can provide useful management information but only if the design is sound, analysis is appropriate, and much care is taken in the interpretation of results.

Applications of logistic regression in a used–unused design in wildlife habitat studies often suffer from asymmetry of errors: used resource units (landscape locations) are known with certainty, whereas unused resource units might be observed to be used with greater sampling intensity. More appropriate might be to use logistic regression to estimate a resource selection function (RSF) tied to a use–availability design based on independent samples drawn from used and available resource units. We review the theoretical motivation for RSFs and show that sample “contamination” and the exponential form commonly assumed for the RSF are not concerns, contrary to recent statements by Keating and Cherry (2004; Use and interpretation of logistic regression in habitat-selection studies. Journal of Wildlife Management 68:774–789). To do this, we re-derive the use–availability likelihood and show that it can be maximized by logistic regression software. We then consider 2 case studies that illustrate our findings. For our first case study, we fit both RSFs and resource selection probability functions (RSPF) to point count data for 4 bird species with varying levels of occurrence among sample blocks. Drawing on our new derivation of the likelihood, we sample available resource units with replacement and assume overlapping distributions of used and available resource units. Irrespective of overlap, we observed approximate proportionality between predictions of a RSF and RSPF. For our second case study, we evaluate the classic use-availability design suggested by Manly et al. (2002), where availability is sampled without replacement, and we systematically introduce contamination to a sample of available units applied to RSFs for woodland caribou (Rangifer tarandus caribou). Although contamination appeared to reduce the magnitude of one RSF beta coefficient, change in magnitude exceeded sampling variation only when >20% of the available units were confirmed caribou use locations (i.e., contaminated). These empirically based simulations suggest that previously recommended sampling designs are robust to contamination. We conclude with a new validation method for evaluating predictive performance of a RSF and for assessing if the model deviates from being proportional to the probability of use of a resource unit.

Resource availability and resource use are 2 key concepts in studies of resource selection. Although equal accessibility to resources is one component defining resource availability, we rarely know what restricts access to resources. Consequently for spatially distributed resources, the animal's use of space in association with the occurrence of resources is a frequent basis for inferring resource use and testing for resource selection. For many resources, occurrence can be defined for the population or the individual animal and requires that researchers specify the spatial extent of resources an animal might use during the time interval of study (e.g., the “choice set”). Often the occurrence of resources is defined at multiple scales, which facilitates understanding hierarchical selection patterns. We discuss numerous factors and criteria that should be considered when delineating the area an animal might use during a period of interest. New analytical approaches to resource selection, including resource utilization functions (RUF) and discrete choice modeling, help address some of the issues of defining availability and dealing with the behaviors associated with resource use. A currency of use is a measure of the investment made by an animal in securing resources, avoiding loss of resources, or otherwise optimizing fitness. Common currencies used by researchers include time spent or distance traveled in a cover type, use of event sites (e.g., nest sites, roosting sites, den sites), or amounts of different kinds of foods consumed. Less common, but potentially highly informative, are such currencies as energy expended or predation risk or other risk incurred. Simulation of animal movements interspersed with diel resting periods, through habitat types with activity-dependent energy expenditure and habitat-specific predation risk showed that choice of a currency of use strongly influences inferences about habitat selection. We argue that perhaps the most informative currency of use would be increased risk to fitness accepted by an animal. Although fairly simple conceptually, such application of risk assessment faces formidable empirical challenges and is a worthy goal for the next generation of researchers of animal resource selection.

Resource-selection probability functions and occupancy models are powerful methods of identifying areas within a landscape that are highly used by a species. One common design/analysis method for estimation of a resource-selection probability function is to classify a sample of units as used or unused and estimate the probability of use as a function of independent variables using, for example, logistic regression. This method requires that resource units are correctly classified as unused (i.e., the species is never undetected in a used unit), or that the probability of misclassification is the same for all units. In this paper, I explore these issues, illustrating how misclassifying units as unused may lead to incorrect conclusions about resource use. I also show how recently developed occupancy models can be utilized within the resource-selection context to improve conclusions by explicitly accounting for detection probability. These models require that multiple surveys be conducted at each of a sample of resource units within a relatively short timeframe, but given the growing evidence from simulation studies and field data, I recommend that such procedures should be incorporated into studies of resource use.

Discrete-choice models are a powerful and flexible method for studying habitat selection, in part because they allow resource availability to change at every choice. Here, we consider application of discrete-choice models to data typically collected in wildlife science because different discrete-choice data are usually collected in other disciplines. We generalize the classic discrete-choice model to the situation in which multiple choices are made from 1 or more choice sets, and only 1 random sample from each choice set is available. We discuss analysis using 1) logistic regression, 2) maximum likelihood when choices are made with replacement, 3) maximum likelihood when the temporal order of selection is known, and 4) maximum likelihood when the order of selection is unknown. We show that 1) provides a good approximation to discrete choice models if the expected number of uses is much <1 for all units. We show that 2) and 3) can be fit using stratified Cox proportional hazards software. Analysis 4) must be fit using special purpose maximization routine such as Newton-Raphson. Finally, we demonstrate 2) on a case study of nightime habitat selection by 28 northern spotted owls (Strix occidentalis caurina), and conclude that these owls selected for locations low on the slope in stands >41 years old with high levels of hardwoods adjacent to stands 6–20 yrs old.

Often resource selection functions (RSFs) are developed by comparing resource attributes of used sites to unused or available ones. We present alternative approaches to the analysis of resource selection based on the utilization distribution (UD). Our objectives are to describe the rationale for estimation of RSFs based on UDs, offer advice about computing UDs and RSFs, and illustrate their use in resource selection studies. We discuss the 3 main factors that should be considered when using kernel UD-based estimates of space use: selection of bandwidth values, sample size versus precision of estimates, and UD shape and complexity. We present 3 case studies that demonstrate use of UDs in resource selection modeling. The first example demonstrates the general case of RSF estimation that uses multiple regression adjusted for spatial autocorrelation to relate UD estimates (i.e., the probability density function) to resource attributes. A second example, involving Poisson regression with an offset term, is presented as an alternative for modeling the relative frequency, or probability of use, within defined habitat units. This procedure uses the relative frequency of locations within a habitat unit as a surrogate of the UD and requires relatively fewer user-defined options in the modeling of resource selection. Last, we illustrate how the UD can also be used to enhance univariate resource selection analyses, such as compositional analysis, in cases where animals use their range nonrandomly. The UD helps overcome several common shortcomings of some other analytical techniques by treating the animal as the primary sampling unit, summarizing use in a continuous and probabilistic manner, and relying on the pattern of animal space use rather than using individual sampling points. However, several drawbacks are apparent when using the UD in resource selection analyses. Choice of UD estimator is important and sensitive to sample size and user-defined options, such as bandwidth and software selection. Extensions to these procedures could consider behavioral-based approaches and alternative techniques to estimate the UD directly.

Increased levels of natural gas exploration, development, and production across the Intermountain West have created a variety of concerns for mule deer (Odocoileus hemionus) populations, including direct habitat loss to road and well-pad construction and indirect habitat losses that may occur if deer use declines near roads or well pads. We examined winter habitat selection patterns of adult female mule deer before and during the first 3 years of development in a natural gas field in western Wyoming. We used global positioning system (GPS) locations collected from a sample of adult female mule deer to model relative frequency or probability of use as a function of habitat variables. Model coefficients and predictive maps suggested mule deer were less likely to occupy areas in close proximity to well pads than those farther away. Changes in habitat selection appeared to be immediate (i.e., year 1 of development), and no evidence of well-pad acclimation occurred through the course of the study; rather, mule deer selected areas farther from well pads as development progressed. Lower predicted probabilities of use within 2.7 to 3.7 km of well pads suggested indirect habitat losses may be substantially larger than direct habitat losses. Additionally, some areas classified as high probability of use by mule deer before gas field development changed to areas of low use following development, and others originally classified as low probability of use were used more frequently as the field developed. If areas with high probability of use before development were those preferred by the deer, observed shifts in their distribution as development progressed were toward less-preferred and presumably less-suitable habitats.

Modeling the probability of use of land units characterized by discrete and continuous measures, we present a Bayesian random-effects model to assess resource selection. This model provides simultaneous estimation of both individual- and population-level selection. Deviance information criterion (DIC), a Bayesian alternative to AIC that is sample-size specific, is used for model selection. Aerial radiolocation data from 76 adult female caribou (Rangifer tarandus) and calf pairs during 1 year on an Arctic coastal plain calving ground were used to illustrate models and assess population-level selection of landscape attributes, as well as individual heterogeneity of selection. Landscape attributes included elevation, NDVI (a measure of forage greenness), and land cover-type classification. Results from the first of a 2-stage model-selection procedure indicated that there is substantial heterogeneity among cow–calf pairs with respect to selection of the landscape attributes. In the second stage, selection of models with heterogeneity included indicated that at the population-level, NDVI and land cover class were significant attributes for selection of different landscapes by pairs on the calving ground. Population-level selection coefficients indicate that the pairs generally select landscapes with higher levels of NDVI, but the relationship is quadratic. The highest rate of selection occurs at values of NDVI less than the maximum observed. Results for land cover-class selections coefficients indicate that wet sedge, moist sedge, herbaceous tussock tundra, and shrub tussock tundra are selected at approximately the same rate, while alpine and sparsely vegetated landscapes are selected at a lower rate. Furthermore, the variability in selection by individual caribou for moist sedge and sparsely vegetated landscapes is large relative to the variability in selection of other land cover types. The example analysis illustrates that, while sometimes computationally intense, a Bayesian hierarchical discrete-choice model for resource selection can provide managers with 2 components of population-level inference: average population selection and variability of selection. Both components are necessary to make sound management decisions based on animal selection.

Previous research has suggested that free-ranging mourning doves (Zenaida macroura) may ingest spent lead pellets, succumb to lead toxicosis, and die in a relatively short time (i.e., an acute lead toxicosis hypothesis). We tested this hypothesis by administering 157 captive mourning doves 2–24 lead pellets, monitoring pellet retention and short-term survival, and measuring related physiological characteristics. During the 19- to 21-day posttreatment period, 104 doves that received lead pellets died (deceased doves) and 53 survived (survivors); all 22 birds in a control group survived. Within 24-hr of treatment, blood lead levels increased almost twice as fast for deceased doves compared to survivors (F_1,208 = 55.49; P < 0.001). During the first week, heterophil:lymphocyte (H:L) ratios increased twice as fast for deceased doves than with survivors (F_1,198 = 23.14, P < 0.001). Posttreatment survival differed (χ² = 37.4, P < 0.001) among the 5 groups of doves that retained different numbers of pellets, and survival ranged from 0.57 (95% CI: 0.44–0.74) for doves that retained ≤2 lead pellets 2 days posttreatment compared to 0.08 (95% CI: 0.022–0.31) for those doves that retained 13–19 lead pellets on 2 days posttreatment; significant differences existed among the 5 groups. After controlling for dove pretreatment body mass, each additional lead pellet increased the hazard of death by 18.0% (95% CI: 1.132–1.230, P < 0.001) and 25.7% (95% CI: 1.175–1.345, P < 0.001) for males and females, respectively. For each 1-g increase in pretreatment body mass, the hazard of death decreased 2.5% (P = 0.04) for males and 3.8% (P = 0.02) for females. Deceased doves had the highest lead levels in liver (49.20 ± 3.23 ppm) and kidney (258.16 ± 21.85 ppm) tissues, whereas controls showed the lowest levels (liver, 0.08 ± 0.041 ppm; kidney, 0.17 ± 0.10 ppm). For doves dosed with pellets, we observed simultaneous increases in blood lead levels and H:L ratios, whereas packed-cell volume (PCV) values declined. Our results support an acute lead toxicosis hypothesis. Although further research is necessary to investigate the magnitude of lead shot ingestion and toxicosis in mourning doves, we recommend that management agencies initiate development of a long-term strategic plan aimed at implementing a nontoxic shot regulation for mourning dove hunting.

Many statistical procedures and metrics have been developed to analyze animal home-range data. We evaluated a point peeling method that may be useful in the analysis of such data. Our objectives were to 1) identify an appropriate peeling criterion that performs well across the suite of underlying behaviors, and 2) compare sample and expected utilization distribution (UD) curves as the basis of a procedure for classifying animal behavior. We addressed the first objective by comparing 3 peeling criteria: 1) peeling farthest from the sample centroid, 2) peeling farthest from the harmonic mean, and 3) peeling the location that caused the greatest decrease in area of remaining data. We compared these criteria across 5 different biologically plausible home-range behaviors as represented by 5 idealized statistical distributions. Comparison of expected UD curves and those generated from simulated data revealed several important considerations: 1) the centroid peeler offered the most accurate and consistent results, 2) the harmonic mean peeler exhibited particularly large amounts of variability, and 3) the area peeler was not able to consistently identify distributions representing clustered or territorial behavior. We addressed the second objective by comparing sample curves to expected UD curves using the centroid peeler. Results revealed each of the sample UD curves captured the key features of the underlying statistical distribution and hence, when dealing with real samples, the behavior. Further, in several examples, the UD curves identified underlying distributions that were not apparent by visual inspection. Overall, point peeling using the centroid peeling function provided a simple but robust procedure for field biologists that made good use of all the data from a sample. This procedure provided an objective home-range measure and a way of classifying home-range use.

During the summers of 2000–2002, we used radio telemetry to document Eastern Prairie Population (EPP) Canada goose (Branta canadensis interior) brood movements and use of brood-rearing habitat. We compared these data with similar data collected in 1976–1978 (Didiuk 1979), prior to a significant increase in the size of the midcontinent light goose (lesser snow geese [Chen caerulescens] and Ross's geese [C. rossii]) population and consequent habitat alteration near Cape Churchill, Manitoba. Since the late 1970s, use of traditional EPP Canada goose brood-rearing areas by light geese has increased significantly near Cape Churchill, and the density of nesting EPP Canada geese has declined. Alteration of brood-rearing habitat has been hypothesized as a cause of the decline in EPP breeding density, as natal dispersal to more distant brood-rearing areas may influence future recruitment into the local breeding population. In 1976–1978, 20 (95%) of 21 radio-marked broods nesting in beach ridge/sedge meadow habitat moved to salt marsh brood-rearing areas; however, only 5 (19%) of 27 Canada geese, nesting in the same habitat, made initial movements to these traditional salt marsh brood-rearing areas in 2000–2002. In 2000–2002, 30 (75%) of 40 geese with broods made initial movements to beach ridge/sedge meadow habitat—10 of these broods eventually moved to salt-marsh habitats later in the brood-rearing period (χ̄ date = 22 days postmedian hatch). Mean brood home range size from 2001–2002 in coastal and inland habitats nearly doubled compared to the mean brood home range size during 1976–1978. Eastern Prairie Population Canada geese currently use brood-rearing habitat other than the coastal salt marshes they used prior to habitat alteration resulting from foraging by light geese. A shift in the use of brood-rearing habitat could potentially reduce nest densities on the study area if first-time breeders nest closer to distant brood-rearing areas. The impact of alternative brood-rearing habitat on gosling growth and survival for EPP geese is unknown, but foraging in poorer quality brood-rearing habitat may also contribute to the observed decline in nesting density.

Limited information is available about the population dynamics of ducks in the boreal forest. We conducted an analysis of recovery data from 5 species of ducks banded in the boreal forest of Alaska, USA, during 1959–1966, and records of 3 species of ducks banded during 1989–2000, with the objective of examining sources of variation in survival and sampling probability and to complement recent studies of the breeding ecology of ducks in the boreal forest. Survival of ducks during 1959–1966 was species- and year-specific. During 1989–2000, survival of northern pintail (Anas acuta) was age-, sex-, and year-specific. Age-class by sex interaction, without year-specificity, however, best-described survival of mallard (A. platyrhynchos) and green-winged teal (A. crecca). Annual survival of male ducks from the Alaska boreal forest was generally similar to annual survival of the same species banded in the midcontinent. Survival probability of female ducks from the Alaska boreal forest, however, was generally higher than survival of female ducks from midcontinent regions. Sampling probability during 1989–2000 was lower for females than males, and increased after 1996, concurrent with the initiation of electronic band reporting. Our results suggest that patterns of duck survival differ between the boreal forest and the midcontinent, especially for after-hatch-year females. Regional variation in survival and reproduction and the factors affecting these parameters should continue to be monitored and considered in continental management plans.

Although the American black duck (Anas rubripes) has been designated a priority species in eastern North America, no systematic survey has been done in the agricultural lowlands of southern Québec, where the species is suspected to be relatively abundant and cohabits with the mallard (Anas platyrhynchos), often considered as a competing species. During the spring of 1998 and 1999, we surveyed breeding waterfowl in 343 4-km² plots distributed in the lowlands of the St. Lawrence Valley and Lac-Saint-Jean, Canada, and in agricultural areas of Abitibi-Témiscamingue, Canada. American black duck densities were higher in dairy farm and forested landscapes (>39 indicated breeding pairs [IBPs]/100 km²) than in cropland landscapes (8 IBPs/100 km²). Mallard densities were similar across all landscape types (30–43 IBPs/100 km²). Habitat modeling using data derived from satellite imagery indicated that the presence of black ducks decreased with increasing areas of corn, ploughed fields, and deciduous forests, whereas it was favored in areas where topography was undulating with slopes of 10–15%. The same parameters had the opposite effect on mallard presence. The odds of black ducks being present were doubled where mallards were present, indicating that both species seem to be attracted to areas supporting adequate habitats, which contradicts the hypothesis of competition between these 2 species to explain for recent declines in the black duck population. Results of our habitat analyses support the hypothesis that habitat changes may be a primary factor leading to these declines. Dairy farm landscapes are of great importance for black ducks, and the conversion of this type of landscape toward a cropland landscape represents a threat to an important portion of the population of this species.

A goal of many resource selection studies is to identify those habitats selected by a species. However, favorability of a particular habitat feature is likely contingent on such factors as landscape composition, predation risk, and an individual's resource needs. Thus, habitat selection may vary depending on context, and identifying causes of variability in habitat use could increase our understanding of functional aspects of a species' habitat ecology. Clear-cuts afford ruffed grouse (Bonasa umbellus) important escape cover, whereas access routes (roads and trails) and mesic bottomlands are viewed as important foraging areas for this species. We present a study of factors influencing strength of selection (i.e., use–availability) for these 3 habitat features by individual ruffed grouse. We analyzed radiotelemetry data from >1,000 ruffed grouse monitored on 10 study sites in the central and southern Appalachians. Five sites were typified by mixed-mesophytic forests, and 5 were predominantly oak-hickory forests. Selection for clear-cuts was positively related to selection for access routes, but it was inversely related to selection for mesic bottomlands. Selection for mesic bottomlands and selection for access routes were positively related in oak-hickory forests, but they were unrelated in mixed-mesophytic forests. Clear-cuts were more strongly selected in mixed-mesophytic forests, and within each forest type, use of clear-cuts was strongest by adult males. Mesic bottomlands were only selected in oak-hickory forests, and within these forests they were most strongly selected by adult females. Following poor, hard-mast crops, use of access routes by female grouse increased. Use of clear-cuts and bottomlands increased for some or all sex and age classes of grouse following closure of hunting, suggesting that hunting discouraged use of these covers. Animals typically face a trade-off between survival and condition to maximize fitness, and our observations suggest that (relative to one another) male grouse favor refuging habitats whereas females favor foraging areas. At a landscape scale, grouse in areas having oak-hickory forests selected foraging habitats more strongly, whereas those inhabiting mixed-mesophytic forests made greater use of escape cover. Our findings indicate that habitat management prescriptions for Appalachian grouse can be tailored by forest type.

Greater sage-grouse (Centrocercus urophasianus) population declines have been attributed to reduced productivity. Although renesting by sage-grouse may contribute significantly to annual productivity during some years, little information is available on this aspect of sage-grouse reproductive ecology. We investigated the relationship between total plasma protein, age of hen, time of first nest initiation, and time of first nest loss on occurrence of renesting. We captured, assigned age, extracted blood, and radiomarked prelaying, female sage-grouse on 4 study areas during 1999–2004. We monitored radiomarked females from mid-April through June to identify period of nest initiation (early, mid, or late), nest loss (early or late), and renesting activity. We only considered hens that were available to renest (n = 143) for analysis, and we censored those that nested successfully or died during their first nest attempt. Depredation and abandonment accounted for 85% (122/143) and 15% (21/143) of the unsuccessful first nests, respectively. The proportion of hens renesting was 34% (48/143) across all study areas and years. Akaike's Information Criterion model selection indicated that occurrence of renesting varied by age, nest initiation period, nest loss period, and total plasma protein. The best model had low predictive power for any given hen (r ² = 0.296), but validation of the best model indicated that our predictor variables were important for distinguishing renesting status and likely explained substantial temporal and spatial variation in renesting rates. A greater proportion of adults than yearlings renested, and hens that nested early in the nesting season and lost nests early during incubation were the most likely to renest. Hens that renested had greater total plasma protein levels than non-renesting hens independent of age, nest initiation period, and nest loss period. Because sage-grouse depend on exogenous sources of protein for reproduction, land management practices that promote high-quality, prelaying hen habitat could increase dietary protein intake and sage-grouse renesting rates.

Current monitoring efforts for greater prairie-chicken (Tympanuchus cupido pinnatus) populations indicate that populations are declining across their range. Monitoring the population status of greater prairie-chickens is based on traditional lek surveys (TLS) that provide an index without considering detectability. Estimators, such as immigration–emigration joint maximum-likelihood estimator from a hypergeometric distribution (IEJHE), can account for detectability and provide reliable population estimates based on resightings. We evaluated the use of mark–resight methods using radiotelemetry to estimate population size and density of greater prairie-chickens on 2 sites at a tallgrass prairie in the Flint Hills of Kansas, USA. We used average distances traveled from lek of capture to estimate density. Population estimates and confidence intervals at the 2 sites were 54 (CI 50–59) on 52.9 km² and 87 (CI 82–94) on 73.6 km². The TLS performed at the same sites resulted in population ranges of 7–34 and 36–63 and always produced a lower population index than the mark–resight population estimate with a larger range. Mark–resight simulations with varying male:female ratios of marks indicated that this ratio was important in designing a population study on prairie-chickens. Confidence intervals for estimates when no marks were placed on females at the 2 sites (CI 46–50, 76–84) did not overlap confidence intervals when 40% of marks were placed on females (CI 54–64, 91–109). Population estimates derived using this mark–resight technique were apparently more accurate than traditional methods and would be more effective in detecting changes in prairie-chicken populations. Our technique could improve prairie-chicken management by providing wildlife biologists and land managers with a tool to estimate the population size and trends of lekking bird species, such as greater prairie-chickens.

Extensive translocation of wildlife throughout North America has led to concerns regarding taxonomic integrity for a number of species. Often, multiple subspecies or variants were translocated into a common habitat or region, creating the opportunity for hybridization to occur. This issue is of particular concern to managers of wild turkeys (Meleagris gallopavo), a species in which considerable mixing of subspecies has occurred. We aim to quantify the subspecific status and degree of hybridization of individuals within an introduced population of Merriam's turkeys (M. g. merriami) in the Davis Mountains of Texas, USA, and within nearby Rio Grande turkey populations (M. g. intermedia). We used data from the Merriam's source population in New Mexico, USA, as a baseline reference for the genetic characteristics of the Merriam's subspecies. Nineteen years following the introduction event, microsatellite data indicate that the genetic integrity of the introduced population of Merriam's turkeys in the Davis Mountains Preserve has been eroded by both immigration from and hybridization with nearby Rio Grande populations. Data from the mitochondrial control region allow for further characterization of hybrid individuals and indicate that most hybrids were the result of immigrant Rio Grande males mating with resident Merriam's females. Our results attribute to the potential importance of hybridization in wildlife species and suggest that hybridization can be a rapid process capable of drastically altering the evolutionary integrity of animals in a region.

We used pilot data collected in 2001–2004 to compare the power of radar and audiovisual survey approaches to detect trends in breeding population size and differences in trends between populations of marbled murrelets (Brachyramphus marmoratus) in northwestern California. Radar counts of murrelets were almost triple in inland Reserves than in Conservation Areas, and audiovisual counts were 7 times greater. Variation in counts was statistically significant among survey sites but not among years. Although annual variation in radar counts was not statistically significant (P = 0.13), mean radar counts more than tripled from 2001 to 2002, a difference that we considered to be biologically significant, and the radar counts reflected a large increase in the proportion of breeders between these 2 years as determined by radiotelemetry in another study (Acord et al. 2004). Audiovisual counts were much more variable than radar counts overall (CV = 1.10 versus 0.41) and within survey sites (CV = 0.94 versus 0.23). As a result, approximately twice the audiovisual survey effort was needed to detect trends with reasonable power (80%). Power to detect trends in murrelet breeding populations was most sensitive to the duration of the monitoring program and the magnitude of the trend; only relatively modest gains in power were realized by increasing the number of surveys or sites. A monitoring program designed to detect differences in trends between breeding murrelet populations required greater survey effort than a program designed to detect overall trends. Despite the fact that gains in power to detect trends from using radar were offset by the cost of purchasing radar equipment, we advocate the use of radar over audiovisual surveys for monitoring murrelet breeding populations because radar reflected changes in breeding effort whereas audiovisual surveys did not. We also advocate the use of radar because it may provide an estimate of the number of breeding individuals in certain situations, it can be used under poor viewing conditions, it samples larger areas, and it detects a higher proportion of inland-flying murrelets.

Radar and audiovisual surveys are important tools for identifying nesting habitat and developing inland conservation strategies for the marbled murrelet (Brachyramphus marmoratus), a threatened seabird that nests in old-growth forests in the Pacific Northwest, USA. Theoretically, counts from these 2 approaches (radar and audiovisual surveys) in different habitats depend on both habitat-specific densities and detection probabilities, which could result in spurious or mask differences among habitats if murrelets are more detectable in certain habitat types. Therefore, we used simultaneous audiovisual and radar surveys to estimate detection probabilities and quantify the relationship between detection probabilities and habitat in coastal redwood forests of northern California, USA. Radar and audiovisual counts were highly correlated (r = 0.65) based on 156 simultaneous surveys, but audiovisual surveys detected only 20.2% (2.6 SE) of murrelets detected by radar, whereas radar detected 75.6% (6.3 SE) of murrelets detected by audiovisual surveys. Murrelets tended to be easier to detect with both audiovisual and radar surveys when there were relatively large areas (>35 ha) of unharvested, old-growth forest at the survey site, probably because birds tended to fly slower and circled more over old growth. Detection probabilities were strongly affected by a variety of other factors including weather, time relative to sunrise, observer, and murrelet behavior. Murrelet counts were positively but weakly correlated to the area of unharvested old growth at the survey site for audiovisual and radar surveys, but this relationship disappeared when we corrected for the effect of habitat on detection probabilities. Our results indicate that raw counts should not be used as indices of nesting densities in different habitats and underscore the need to model heterogeneity in detection probabilities among habitats using available sampling designs and statistical methods. Nevertheless, we recommend using radar instead of audiovisual surveys for counting murrelets in forested areas because detection probabilities were much higher for radar than audiovisual surveys, radar is less likely to detect the same group of murrelets multiple times, and radar surveys can be conducted in poor viewing and hearing conditions.

For many avian species, predation is the leading cause of nest failure. However, relationships between predator abundance and nest predation often differ across spatial scales. We examined the relationship between environmental characteristics in meadows and mammalian predator activity, the relationship between predator activity at 2 spatial scales, and the probability of nest predation of willow flycatchers (Empidonax traillii), dusky flycatchers (Empidonax oberholseri), and yellow warblers (Dendroica petechia) in the central Sierra Nevada Mountains, California, USA. Environmental characteristics associated with the detection of nest predators varied depending on species. Douglas's squirrel (Tamiasciurus douglasii) and chipmunks (Tamias spp.) were associated with characteristics common along edges of meadows; short-tailed weasels (Mustela erminea) were associated with willows, whereas mice (Peromyscus maniculatus, Reithrodontomys megalotis, and Microtus spp.) and long-tailed weasels (Mustela frenata) were distributed throughout the meadows. The probability of predation of willow and dusky flycatcher nests increased with increasing short-tailed weasel activity, and the probability of predation of yellow warbler nests increased with increasing activity of chipmunks and short-tailed weasels. Variation in the occurrence of predator species in different areas of the meadows likely influences the probability of nest predation by each species and the nesting success of birds. Identifying factors that influence the distribution and abundance of common nest predators will likely be integral to the development of conservation efforts to increase the reproductive success of some bird species.

We examined factors affecting the nesting success of a migratory songbird, the Acadian flycatcher (Empidonax virescens), in loblolly pine plantations in the coastal plain of South Carolina, USA. From 1997–2000, we located and monitored 163 Acadian flycatcher nests in loblolly pine stands and corridors that were 18–27 years old. We used Mayfield logistic regression (Aebischer 1999, Hazler 2004) to model the effects of edge and stand-level vegetation structure on nest daily survival rate. There was no evidence of an effect of edge on nest survival, but nest survival was positively related to the height of the deciduous subcanopy and to the density of shrub cover. Although Acadian flycatchers are generally regarded as habitat specialists requiring mature hardwood forests, our data suggest that pine plantations can support breeding populations, provided that a substantial hardwood component is present. We believe that maintaining multiple vegetation strata and increasing the length of harvest rotations would improve the habitat value of pine plantations for Acadian flycatchers and presumably other species more typically associated with deciduous forests. Maintenance of a corridor network, as practiced by some industrial forest managers, is one means of providing more mature forest habitat, thereby fostering higher nesting success. Concern that these corridors might act as ecological traps seems to be unwarranted in our study area. Corridors thus appear to be a valuable management tool for promoting wildlife values within the context of an industrial forest landscape.

Harvesting of marine and terrestrial animals by humans produces animal biomass byproducts that many scavenger species exploit. Effects of food byproducts from harvesting on the ecology of scavenger species has rarely been measured, especially in terrestrial systems. Such nutritional subsidization of scavengers needs to be monitored because increases in their populations may influence population dynamics of other species and alter natural community dynamics. I quantified effects of the distribution of elk (Cervus elaphus) gutpiles generated by an intensive harvest program in Jackson Hole, Wyoming, USA, on local raven (Corvus corax) foraging behaviors, daily and seasonal movements, and population distribution. During Jackson Hole's 2001 fall elk harvest, I found ravens to be the most abundant vertebrate species scavenging on monitored gutpiles, and the number of ravens I detected during fixed-width transect surveys positively correlated with concurrent, sympatric gutpile densities. I found raven abundance, estimated via point-count surveys in habitat-paired harvest zone and reference plots, to increase significantly in conjunction with the fall elk harvest only in the harvest zone plots. Furthermore, estimated raven abundance and nest density in the spring were significantly higher in the harvest zone plots than in the reference plots. Results indicate that in Jackson Hole, ravens exploit gutpiles provided by elk harvesting, daily raven distribution in the fall corresponds with the immediate distribution of gutpiles across the landscape, fall raven abundance is associated with the overall density of gutpiles in a given area in the fall, and spring raven abundance and nest density are associated with fall gutpile density. Collectively, these findings suggest that the high concentration of elk gutpiles in Jackson Hole is a significant supplemental food resource for ravens, and that wildlife harvesting in a terrestrial environment is capable of influencing the foraging behaviors, movements, and population dynamics of scavenger species. Wildlife managers must consider nontarget species when evaluating the efficacy of their regulatory programs and work to minimize unintended effects caused by wildlife management on the surrounding ecological community. Jackson Hole's elk population regulation program is a model for ungulate management due to its long-term success, while at the same time managers in Jackson Hole are continually addressing how their program may affect the surrounding ecological community and considering alternative management strategies to more effectively conserve the region's diversity. Results here provide baseline information on raven ecology in relation to Jackson Hole's current elk management program for comparison to other areas with intensive ungulate management programs, and for later comparison within Jackson Hole as strategies for managing its elk population change in the future. This study also draws attention toward monitoring effects of anthropogenic byproduct food resources that, despite their inconspicuousness in the literature, can substantially influence the ecology of opportunistic scavengers; and it points out several scavenger species other than ravens that also may be influenced by access to gutpiles or other anthropogenic foods that are abundant, reliable, and nutritious. Finally, having determined a clear link between elk harvesting and the population dynamics of ravens—an influential species in its ecological community—this study sets the stage for future research, testing the strength and extent of a trophic cascade that may be initiated by gutpile availability and propagated by increases in raven population density in Jackson Hole.

Chronic wasting disease (CWD) is a fatal disease of white-tailed deer (Odocoileus virginianus) caused by transmissible protease-resistant prions. Since the discovery of CWD in southern Wisconsin in 2001, more than 20,000 deer have been removed from a >2,500-km² disease eradication zone surrounding the three initial cases. Nearly all deer removed were tested for CWD infection and sex, age, and harvest location were recorded. Our analysis used data from a 310-km² core study area where disease prevalence was higher than surrounding areas. We found no difference in harvest rates between CWD infected and noninfected deer. Our results show that the probability of infection increased with age and that adult males were more likely to be infected than adult females. Six fawns tested positive for CWD, five fawns from the core study area, including the youngest (5 months) free-ranging cervid to test positive. The increase in male prevalence with age is nearly twice the increase found in females. We concluded that CWD is not randomly distributed among deer and that differential transmission among sex and age classes is likely driving the observed patterns in disease prevalence. We discuss alternative hypotheses for CWD transmission and spread and, in addition, discuss several possible nonlinear relationships between prevalence and age. Understanding CWD transmission in free-ranging cervid populations will be essential to the development of strategies to manage this disease in areas where CWD is found, as well as for surveillance strategies in areas where CWD threatens to spread.

Gray wolf (Canis lupus) populations have persisted and expanded in northwest Montana since 1986, while reintroduction efforts in Idaho and Yellowstone have further bolstered the regional population. However, rigorous analysis of either the availability of wolf habitat in the entire region, or the specific habitat requirements of local wolves, has yet to be conducted. We examined wolf-habitat relationships in the northern Rocky Mountains of the U.S. by relating landscape/habitat features found within wolf pack home ranges (n = 56) to those found in adjacent non-occupied areas (n = 56). Logistic regression revealed that increased forest cover, lower human population density, higher elk density, and lower sheep density were the primary factors related to wolf occupation. Similar factors promoted wolf pack persistence. Further, our analysis indicated that relatively large tracts of suitable habitat remain unoccupied in the Rocky Mountains, suggesting that wolf populations likely will continue to increase in the region. Analysis of the habitat linkage between the 3 main wolf recovery areas indicates that populations in central Idaho and northwest Montana have higher connectivity than either of the 2 recovery areas to the Greater Yellowstone recovery area. Thus, for the northern Rocky Mountains to function as a metapopulation for wolves, it will be necessary that dispersal corridors to the Yellowstone ecosystem be established and conserved.

Understanding factors underlying nest-site selection is important for effective conservation and management of a declining and economically important species. We measured vegetation characteristics at nest sites of northern bobwhites (Colinus virginianus; hereafter, bobwhites) and at random points in the Texas Panhandle. We used these data to develop a neural network classification model for predicting nest-site suitability. We also compared the characteristics of successful nests with those of failed nests using the bootstrapping method. We monitored a subset of nests using video cameras during incubation and for 3 days postcompletion (succeeded or failed) to determine nest fate, cause of fate, and nest activity after completion. Nest-canopy height, percent shrub cover, and bare-ground exposure were important vegetation characteristics influencing nest-site selection. Sites became more suitable as canopy height exceeded 40 cm, shrub cover exceeded 25%, and as bare-ground exposure fell below 30%. Successful nests had higher canopies and more shrub cover than failed nests, but successful nests had more bare ground than failed nests. Nest visits were common at monitored nests after nest completion (failed, successful). Most visitors were adult bobwhites, but other species also visited nests. Such visits might bias the determination of nest fate if the determination is based on nest remains, especially if nests are not monitored daily. Bobwhites might select nest sites to maximize nest concealment compared with random locations.

During the 1999 and 2000 spring and summer seasons, we collected and analyzed 544 eggs, 273 from background sites and 271 from mining sites to measure and compare selenium (Se) levels. We collected and analyzed eggs from 31 avian species. Our data indicated an increase in Se levels in birds on mining sites, i.e., 16 of 24 species (67%) had significantly higher Se levels. The remaining species did not have large enough sample sizes for statistical tests. For all eggs collected on mining sites, the distribution of Se levels was as follows: 57% were less than 5 ppm, 30% were between 5 and 10 ppm, 8% were between 10 and 16 ppm, and 5% were >16 ppm. We concluded that relatively few birds (i.e., <8%) that occupied habitats associated with mining activity in southeast Idaho have Se levels that exceed the threshold level recommended by Adams et al. (2002). In 2001 we obtained reproductive data on 298 American robin (Turdus migratorius) nests and 325 red-winged blackbird (Agelaius phoeniceus) nests. Analysis included nest success, clutch size, hatching success, fledging success, egg weight, and neonate weight. Thus, we had 12 measures of reproduction for comparison between mining and background sites. We found no significant difference between sites for 11 of these measures. The remaining measure, nest success for robins, was significantly higher in mining sites.